Local SQL Help
February 07, 2012 Tuesday

Typographical conventions

To ensure clarity in the SQL syntax examples and pseudo-code, the typographical conventions that follow are used throughout the local SQL help.
 

SQL statements

Each topic contains a pseudo-code prototype of an SQL statement or part of a statement that demonstrates the language element discussed. These prototype examples appear at the beginning of topics. Actual SQL statements appear within topics that demonstrate actual use of the language element discussed. Both the prototype and example statements appear in Courier New font.
While the local SQL language itself is case-insensitive (language elements and metadata object names), examples in this help file use the following convention to differentiate between language and metadata objects. All language elements appear in uppercase. Metadata names appear in lowercase. Correlation names appear in mixed case.

Optional elements

Language elements that are available, but that do not have to be used with an SQL statement for the statement to be valid appear in prototype syntax examples in brakets ([ and ]). For example, in the line below, the DISTINCT keyword is optional.

SELECT [DISTINCT] *

Syntax choices

When there is a choice between one of a number of possible syntax elements, such choices will be listed in prototype syntax examples separated by the vertical bar character (|). Unless also enclosed in brackets to make the group of choices optional, one of the group of choices must be used in the statement. In the prototype syntax example below, the SQL statement may include either the ASC or the DESC keyword, but not both. Because the list of choices (ASC and DESC) is enclosed in brackets, use of either keyword is optional.

ORDER BY column_reference [ASC | DESC]
Note Do not mistake the choice typographical symbol for the concatenation function, defined as two vertical bar characters together (||).

TABLE NAMES

ANSI-standard SQL confines each table name to a single word comprised of alphanumeric characters and the underscore symbol, "_". Local SQL, however, is enhanced to support multi-word table names.
Local SQL supports full file and path specifications in table references. Table references with path or filename extensions must be enclosed in single or double quotation marks. For example:

SELECT *
FROM 'parts.dbf'
SELECT *
FROM "c:\sample\parts.dbf"
Local SQL also supports BDE aliases in table references. For example:
SELECT *
FROM ":pdox:table1"
If you omit the file extension for a local table name, the table is assumed to be the table type specified in the BDE configuration. The default table type is specified either in the default driver setting or in the default driver type for the standard alias associated with the query.
Finally, local SQL permits table names to duplicate SQL keywords as long as those table names are enclosed in single or double quotation marks. For example:
SELECT passid
FROM "password"

COLUMN NAMES

ANSI-standard SQL confines each column name to a single word comprised of alphanumeric characters and the underscore symbol, "_". Local SQL, however, is enhanced to support multi-word column names.
Local SQL supports Paradox multi-word column names and column names that duplicate SQL keywords as long as those column names are
Enclosed in single or double quotation marks
Prefaced with an SQL table name or table correlation name
For example, the following column name consists of two words:

SELECT E."Emp Id"
FROM employee E
In the next example, the column name is the same as the SQL keyword DATE:
SELECT datelog."date"
FROM datelog

DATE FORMATS

Local SQL expects date literals to be in a U.S. date format, MM/DD/YY or MM/DD/YYYY. International date formats are not supported. To prevent date literals from being mistaken by the SQL parser for arithmetic calculations, enclose them in quotation marks. This keeps 1/23/1998 from being mistaken for 1 divided by 23 divided by 1998.

SELECT *
FROM orders
WHERE (saledate <= "1/23/1998")
Leading zeros for the month and day fields are optional.
If the century is not specified for the year, the BDE setting FOURDIGITYEAR controls the century. If FOURDIGITYEAR is set to FALSE and the year is specified with only two digits, years 49 and less will be prefiex with 20 and years 50 and higher with 19. If
For example, with FOURDIGITYEAR set to FALSE, the SQL statement below returns rows where the SaleDate column contains dates of “5/5/1980” or “5/5/2030”.
SELECT *
FROM orders
WHERE (saledate = "5/5/30") OR (saledate = "5/5/80")
To query using years outside these bounds, specify the century in the date literal.
SELECT *
FROM orders
WHERE (saledate = "5/5/1930") OR (saledate = "5/5/2080")

TIME FORMATS

Local SQL expects time literals to be in the format hh:mm:ss AM/PM; where hh are the hours, mm the minutes, and ss the seconds. When inserting new data with a time value, the AM/PM designator is optional and is case-insensitive ("AM" is the same as "am"). The time literal must be enclosed in quotation marks.

INSERT INTO WorkOrder
(ID, StartTime)
VALUES ("B00120","10:30:00 PM")
Indicate which half of the day (morning or after noon) a time literal falls under in one of two ways. If an AM or PM marker is specified, that determines the half of the day. If no AM/PM designator is specified, the hour field is compared to 12. If the hour is less than twelve, the time is in the AM; if greater than 12, after noon. The hour field overrides an AM/PM designator. For example, the time literal "15:03:22 AM" is translated as "3:03:22 PM".

BOOLEAN LITERALS

The boolean literal values TRUE and FALSE may be represented with or without quotation marks.

SELECT *
FROM transfers
WHERE (paid = TRUE) AND NOT (incomplete = "FALSE")

TABLE CORRELATION NAMES

Table correlation names are used to explicitly associate a column with the table from which it comes. This is especially useful when multiple columns of the same name appear in the same query, typically in multi-table queries. A table correlation name is defined by following the table reference in the FROM clause of a SELECT query with a unique identifier. This identifier, or table correlation name, can then be used to prefix a column name.
If the table name is not a quoted string, the table name is the default implicit correlation name. An explicit correlation name the same as the table name need not be specified in the FROM clause and the table name can prefix column names in other parts of the statement.

SELECT *
FROM customer
LEFT OUTER JOIN orders
ON (customer.custno = orders.custno)
If the table name is a quoted string, you need to do one of the following:
Prefix column names with the exact quoted string used for the table in the FROM clause.
SELECT *
FROM "customer.db"
LEFT OUTER JOIN "orders.db"
ON ("customer.db".custno = "orders.db".custno)
Use the full table name as a correlation name in the FROM clause (and prefix all column references with the same correlation name).
SELECT *
FROM "customer.db" CUSTOMER
LEFT OUTER JOIN "orders.db" ORDERS
ON (CUSTOMER.custno = ORDERS.custno)
Use a distinct token as a correlation name in the FROM clause (and prefix all column references with the same correlation name).
SELECT *
FROM "customer.db" C
LEFT OUTER JOIN "orders.db" O
ON (C.custno = O.custno)

COLUMN CORRELATION NAMES

Use the AS keyword to assign a correlation name to a column, aggregated value, or literal. Column correlation names cannot be enclosed in quotation marks and so cannot contain embedded spaces.

SELECT SUBSTRING(company FROM 1 FOR 1) AS sub, "Text" AS word
FROM customer

RESERVED WORDS

Below is an alphabetical list of words reserved by local SQL. Avoid using these reserved words for the names of metadata objects (tables, columns, and indexes). An "Invalid use of keyword error" occurs when reserved words are used as names for metadata objects. If a metadata object must have a reserved word as it name, prevent the error by enclosing the name in quotation marks and prefixing the reference with the table name.
ACTIVE ADD ALL AFTER ALTER AND ANY AS ASC ASCENDING AT AUTO AUTOINC AVG BASE_NAME BEFORE BEGIN BETWEEN BLOB BOOLEAN BOTH BY BYTES CACHE CAST CHAR CHARACTER CHECK CHECK_POINT_LENGTH COLLATE COLUMN COMMIT COMMITTED COMPUTED CONDITIONAL CONSTRAINT CONTAINING COUNT CREATE CSTRING CURRENT CURSOR DATABASE DATE DAY DEBUG DEC DECIMAL DECLARE DEFAULT DELETE DESC DESCENDING DISTINCT DO DOMAIN DOUBLE DROP ELSE END ENTRY_POINT ESCAPE EXCEPTION EXECUTE EXISTS EXIT EXTERNAL EXTRACT FILE FILTER FLOAT FOR FOREIGN FROM FULL FUNCTION GDSCODE GENERATOR GEN_ID GRANT GROUP GROUP_COMMIT_WAIT_TIME HAVING HOUR IF IN INT INACTIVE INDEX INNER INPUT_TYPE INSERT INTEGER INTO IS ISOLATION JOIN KEY LONG LENGTH LOGFILE LOWER LEADING LEFT LEVEL LIKE LOG_BUFFER_SIZE MANUAL MAX MAXIMUM_SEGMENT MERGE MESSAGE MIN MINUTE MODULE_NAME MONEY MONTH NAMES NATIONAL NATURAL NCHAR NO NOT NULL NUM_LOG_BUFFERS NUMERIC OF ON ONLY OPTION OR ORDER OUTER OUTPUT_TYPE OVERFLOW PAGE_SIZE PAGE PAGES PARAMETER PASSWORD PLAN POSITION POST_EVENT PRECISION PROCEDURE PROTECTED PRIMARY PRIVILEGES RAW_PARTITIONS RDB$DB_KEY READ REAL RECORD_VERSION REFERENCES RESERV RESERVING RETAIN RETURNING_VALUES RETURNS REVOKE RIGHT ROLLBACK SECOND SEGMENT SELECT SET SHARED SHADOW SCHEMA SINGULAR SIZE SMALLINT SNAPSHOT SOME SORT SQLCODE STABILITY STARTING STARTS STATISTICS SUB_TYPE SUBSTRING SUM SUSPEND TABLE THEN TIME TIMESTAMP TIMEZONE_HOUR TIMEZONE_MINUTE TO TRAILING TRANSACTION TRIGGER TRIM UNCOMMITTED UNION UNIQUE UPDATE UPPER USER VALUE VALUES VARCHAR VARIABLE VARYING VIEW WAIT WHEN WHERE WHILE WITH WORK WRITE YEAR
The following are operators used in local SQL. Avoid using these characters in the names of metadata objects.
||, -, *, /, <>, <, >, ,(comma), =, <=, >=, ~=, !=, ^=, (, )

DML STATEMENT LIST

Local SQL supports the following data manipulation language (DML) statements:

  • DML Statements Description
  • SELECTRetrieves existing data from a table.
  • DELETE Deletes existing data from a table.
  • INSERT Adds new data to a table.
  • UPDATE Modifies existing data in a table.

SELECT STATEMENT

Retrieves data from tables.

SELECT [DISTINCT] * | column_list
FROM table_reference
[WHERE predicates]
[ORDER BY order_list]
[GROUP BY group_list]
[HAVING having_condition]

Use the SELECT statement to:
-Retrieve a single row, or part of a row, from a table, referred to as a singleton select.
-Retrieve multiple rows, or parts of rows, from a table.
-Retrieve related rows, or parts of rows, from a join of two or more tables.
The SELECT clause defines the list of items returned by the SELECT statement. The SELECT clause uses a comma-separated list composed of: table columns, literal values, and column or literal values modified by functions. Literal values in the columns list may be passed to the SELECT statement via parameters. You cannot use parameters to represent column names. Use an asterisk to retrieve values from all columns.
Columns in the column list for the SELECT clause may come from more than one table, but can only come from those tables listed in the FROM clause. See Relational Operators for more information on using the SELECT statement to retrieve data from multiple tables.
The FROM clause identifies the table(s) from which data is retrieved.
The following statement retrieves data for two columns in all rows of a table.
SELECT custno, company
FROM orders
Use DISTINCT to limit the retrieved data to only distinct rows. The distinctness of rows is based on the combination of the columns in the SELECT clause columns list.
In lieu of a table, a SELECT statement may retrieve rows from a Paradox-style .QBE file. This is an approximation of an SQL view.
SELECT *
FROM "customers.qbe"

DELETE

Deletes one or more rows from a table.

DELETE FROM table_reference
[WHERE predicates]
Description
Use DELETE to delete one or more rows from an existing table.
DELETE FROM "employee.db"
The optional WHERE clause restricts row deletions to a subset of rows in the table. If no WHERE clause is specified, all rows in the table are deleted.
DELETE FROM "employee.db"
WHERE (empno IN (SELECT empno FROM "old_employee.db"))
The table reference cannot be passed to the DELETE statement via a parameter.

INSERT

Adds one or more new rows of data in a table

INSERT INTO table_reference
[(columns_list)]
VALUES (update_atoms)
Description
Use the INSERT statement to add new rows of data to a table.
Use a table reference in the INTO clause to specify the table to receive the incoming data.
The columns list is a comma-separated list, enclosed in parentheses, of columns in the table and is optional. The VALUES clause is a comma-separated list of update atoms, enclosed in parentheses. If no columns list is specified, incoming update values (update atoms) are stored in fields as they are defined sequentially in the table structure. Update atoms are applied to columns in the order the update atoms are listed in the VALUES clause. There must also be as many update atoms as there are columns in the table.
INSERT INTO "holdings.dbf"
VALUES (4094095, "BORL", 5000, 10.500, "1/2/1998")
If an explicit columns list is stated, incoming update atoms (in the order they appear in the VALUES clause) are stored in the listed columns (in the order they appear in the columns list). NULL values are stored in any columns that are not in a columns list.
INSERT INTO "customer.db"
(custno, company)
VALUES (9842, "Borland International, Inc.")
To add rows to one table from another, omit the VALUES keyword and use a subquery as the source for the new rows.
INSERT INTO "customer.db"
(custno, company)
SELECT custno, company
FROM "oldcustomer.db"
Update atom values may be passed to the INSERT statement via parameters. You cannot use parameters for the table reference and columns list.
Note Insertion of one or multiple rows from one table to another through a subquery is not supported.

UPDATE

Modifies one or more existing rows in a table.

UPDATE table_reference
SET column_ref = update_atom [, column_ref = update_atom...]
[WHERE predicates]
Description
Use the UPDATE statement to modify one or more column values in one or more existing rows in a table.
Use a table reference in the UPDATE clause to specify the table to receive the data changes.
The SET clause is a comma-separated list of update expressions. Each expression is composed of the name of a column, the assignment operator (=), and the update value (update atom) for that column. The update atoms in any one update expression may be literal values, singleton return values from a subquery, or update atoms modified by functions. Subqueries supplying an update atom for an update expression must return a singleton result set (one row) and return only a single column.
UPDATE salesinfo
SET taxrate = 0.0825
WHERE (state = "CA")
Update atom values may be passed to the UPDATE statement via parameters. You cannot use parameters for the table reference and columns list.
The optional WHERE clause restricts updates to a subset of rows in the table. If no WHERE clause is specified, all rows in the table are updated using the SET clause update expressions.

CLAUSE LIST

Local SQL supports the following SQL statement clauses:

  • FROM Specifies the tables used for the statement.
  • WHERE Specifies filter criteria to limit rows retrieved.
  • ORDER BY Specifies the columns on which to sort the result set.
  • GROUP BY Specifies the columns used to group rows.
  • HAVING Specifies filter criteria using aggregated data.

FROM

Specifies the tables from which a SELECT statement retrieves data.

FROM table_reference [, table_reference...]
Description
Use a FROM clause to specify the table or tables from which a SELECT statement retrieves data. The value for a FROM clause is a comma-separated list of table names. Specified table names must follow local SQL naming conventions for tables. For example, the SELECT statement below retrieves data from a single Paradox table.
SELECT *
FROM "customer.db"
See the section Relational Operators for more information on retrieving data from multiple tables in a single SELECT query.
The table reference cannot be passed to a FROM clause via a parameter.

WHERE

Specifies filtering conditions for a SELECT or UPDATE statement.
WHERE predicates
Description
Use a WHERE clause to limit the effect of a SELECT or UPDATE statement to a subset of rows in the table. Use of a WHERE clause is optional.
The value for a WHERE clause is one or more logical expressions, or predicates, that evaluate to TRUE or FALSE for each row in the table. Only those rows where the predicates evaluate to TRUE are retrieved by a SELECT statement or modified by an UPDATE statement. For example, the SELECT statement below retrieves all rows where the STATE column contains a value of "CA".

SELECT company, state
FROM customer
WHERE state = "CA"
Multiple predicates must be separated by one of the logical operators OR or AND. Each predicate can be negated with the NOT operator. Parentheses can be used to isolate logical comparisons and groups of comparisons to produce different row evaluation criteria. For example, the SELECT statement below retrieves all rows where the STATE column contains a value of "CA" and those with a value of "HI".
SELECT company, state
FROM customer
WHERE (state = "CA") OR (state = "HI")
The SELECT statement below retrieves all rows where the SHAPE column is "round" or "square". It also returns those rows where the COLOR column is "red", regardless of the value in the SHAPE column.
SELECT shape, color, cost
FROM objects
WHERE ((shape = "round") AND (shape = "square")) OR (color = "red")
Subqueries are supported in the WHERE clause. A subquery works like a search condition to restrict the number of rows returned by the outer, or "parent" query.
Column references cannot be passed to a WHERE clause via parameters. Comparison values may be passed as parameters.
Note A WHERE clause filters data prior to the aggregation of a GROUP BY clause. For filtering based on aggregated values, use a HAVING clause.
Applicability
SELECT (with non-aggregated columns), UPDATE

ORDER BY

Sorts the rows retrieved by a SELECT statement.

ORDER BY column_reference [, column_reference...] [ASC|DESC]
Description
Use an ORDER BY clause to sort the rows retrieved by a SELECT statement based on the values from one or more columns.
The value for the ORDER BY clause is a comma-separated list of column names. The columns in this list must also be in the SELECT clause of the query statement. Columns in the ORDER BY list can be from one or multiple tables. A number representing the relative position of a column in the SELECT clause may be used in place of a column name. Column correlation names can also be used in an ORDER BY clause columns list.
Use ASC (or ASCENDING) to force the sort to be in ascending order (smallest to largest), or DESC (or DESCENDING) for a descending sort order (largest to smallest). When not specified, ASC is the implied default.
The statement below sorts the result set ascending by the year extracted from the LASTINVOICEDATE column, then descending by the STATE column, and then ascending by the uppercase conversion of the COMPANY column.
SELECT EXTRACT(YEAR FROM lastinvoicedate) AS YY, state, UPPER(company)
FROM customer
ORDER BY YY DESC, state ASC, 3
See the section Relational Operators for more information on retrieving data from multiple tables in a single SELECT query.
Column references cannot be passed to an ORDER BY clause via parameters.
Applicability
SELECT

GROUP BY

Combines rows with column values in common into single rows.

GROUP BY column_reference [, column reference...]
Description
Use a GROUP BY clause to combine rows with the same column values into a single row. The criteria for combining rows is based on the values in the columns specified in the GROUP BY clause. The purpose for using a GROUP BY clause is to combine one or more column values (aggregate) into a single value and provide one or more columns to uniquely identify the aggregated values. A GROUP BY clause can only be used when one or more columns have an aggregate function applied to them.
The value for the GROUP BY clause is a comma-separated list of columns. Each column in this list must meet the following criteria:
Be in one of the tables specified in the FROM clause of the query.
Be in the SELECT clause of the query.
Cannot have an aggregate function applied to it.
When a GROUP BY clause is used, all table columns in the SELECT clause of the query must meet at least one of the following criteria, or it cannot be included in the SELECT clause:
Be in the GROUP BY clause of the query.
Be in the subject of an aggregate function.
Literal values in the SELECT clause are not subject to the preceding criteria.
The distinctness of rows is based on the columns in the column list specified. All rows with the same values in these columns are combined into a single row (or logical group). Columns that are the subject of an aggregate function have their values across all rows in the group combined. All columns not the subject of an aggregate function retain their value and serve to distinctly identify the group. For example, in the SELECT statement below, the values in the SALES column are aggregated (totaled) into groups based on distinct values in the COMPANY column. This produces total sales for each company.
SELECT company, SUM(sales) AS TOTALSALES
FROM sales1998
GROUP BY company
ORDER BY company
A column may be referenced in a GROUP BY clause by a column correlation name, instead of actual column names. The statement below forms groups using the first column, COMPANY, represented by the column correlation name Co.
SELECT company AS Co, SUM(sales) AS TOTALSALES
FROM sales1998
GROUP BY Co
ORDER BY 1
Note Derived values (calculated fields) cannot be used as the basis for a GROUP BY clause.
Column references cannot be passed to an GROUP BY clause via parameters.
Applicability
SELECT when aggregate functions used

HAVING

Specifies filtering conditions for a SELECT statement.
HAVING predicates
Description
Use a HAVING clause to limit the rows retrieved by a SELECT statement to a subset of rows where aggregated column values meet the specified criteria. A HAVING clause can only be used in a SELECT statement when:
The statement also has a GROUP BY clause.
One or more columns are the subjects of aggregate functions.
The value for a HAVING clause is one or more logical expressions, or predicates, that evaluate to true or false for each aggregate row retrieved from the table. Only those rows where the predicates evaluate to true are retrieved by a SELECT statement. For example, the SELECT statement below retrieves all rows where the total sales for individual total sales exceed $1,000.

SELECT company, SUM(sales) AS TOTALSALES
FROM sales1998
GROUP BY company
HAVING (SUM(sales) >= 1000)
ORDER BY company
Multiple predicates must be separated by one of the logical operators OR or AND. Each predicate can be negated with the NOT operator. Parentheses can be used to isolate logical comparisons and groups of comparisons to produce different row evaluation criteria.
A SELECT statement can include both a WHERE clause and a HAVING clause. The WHERE clause filters the data to be aggregated, using columns not the subject of aggregate functions. The HAVING clause then further filters the data after the aggregation, using columns that are the subject of aggregate functions. The SELECT query below performs the same operation as that above, but data limited to those rows where the STATE column is "CA".
SELECT company, SUM(sales) AS TOTALSALES
FROM sales1998
WHERE (state = "CA")
GROUP BY company
HAVING (SUM(sales) >= 1000)
ORDER BY company
Subqueries are supported in the HAVING clause. A subquery works like a search condition to restrict the number of rows returned by the outer, or "parent" query.
Note A HAVING clause filters data after the aggregation of a GROUP BY clause. For filtering based on row values prior to aggregation, use a WHERE clause.
Applicability
SELECT with GROUP BY

FUNCTION LIST

Local SQL supports the following data manipulation language functions:
String function Description
Concatenation Concatenates two string values.

  • LOWER Forces a string to lowercase.
  • UPPER Forces a string to uppercase.
  • SUBSTRING Extracts a portion of a string value.
  • TRIM Removes repetitions of a specified character from the left, right, or both sides of a string.
  • Aggregate function Description
  • AVG Averages all non-NULL numeric values in a column.
  • COUNT Counts the number of rows in a result set.
  • MAX Determines the maximum value in a column.
  • MIN Determines the minimum value in a column.
  • SUM Totals all numeric values in a column.
  • Data function Description
  • CAST Converts values from one data type to another.
  • EXTRACT Extracts the year, month, or day field of a date.

LOWER

Converts all characters to lowercase.

LOWER(column_reference)
Description
Use LOWER to convert all of the characters in a table column or character literal to lowercase. For example, in the SELECT statement below the values in the NAME column appear all in lowercase.
SELECT LOWER(name)
FROM country
When applied to retrieved data of a SELECT statement, the effect is transient and does not affect stored data. When applied to the update atoms of an UPDATE statement, the effect is persistent and permanently converts the case of the stored values.
Applicability
LOWER can only be used with character columns or literals. To use on values of other data types, the values must first be converted to CHAR using the CAST function.
Note: the LOWER function cannot be used with memo or BLOB columns.

UPPER

Converts all characters to uppercase.

UPPER(column_reference)
Description
Use UPPER to convert all of the characters in a table column or character literal to uppercase. For example, in the SELECT statement below the values in the NAME column are treated as all in uppercase. Because the same conversion is applied to both the filter column and comparison value in the WHERE clause, the filtering is effectively case-insensitive.
SELECT name, capital, continent
FROM country
WHERE UPPER(name) LIKE UPPER("Pe%")
When applied to retrieved data of a SELECT statement, the effect is transient and does not affect stored data. When applied to the update atoms of an UPDATE statement, the effect is persistent and permanently converts the case of the stored values.
Applicability
UPPER can only be used with character columns or literals. To use on values of other data types, the values must first be converted to CHAR using the CAST function.
Note: the UPPER function cannot be used with memo or BLOB columns.

SUBSTRING

Extracts a substring from a string.

SUBSTRING(column_reference FROM start_index [FOR length])
Description
Use SUBSTRING to extract a substring from a table column or character literal, specified in the column reference.
FROM is the character position at which the extracted substring starts within the original string. The index for FROM is based on the first character in the source value being 1.
FOR is optional, and specifies the length of the extracted substring. If FOR is omitted, the substring goes from the position specified by FROM to the end of the string.
The example below, applied to the literal string "ABCDE" returns the value "BCD".
SELECT SUBSTRING("ABCDE" FROM 2 FOR 3) AS Sub
FROM country
In the SELECT statement below only the second and subsequent characters of the NAME column are retrieved.
SELECT SUBSTRING(name FROM 2)
FROM country
When applied to retrieved data of a SELECT statement, the effect is transient and does not affect stored data. When applied to the update atoms of an UPDATE statement, the effect is persistent and permanently converts the case of the stored values.
Applicability
SUBSTRING can only be used with character columns or literals. To use on values of other data types, the values must first be converted to CHAR using the CAST function.
Note: the SUBSTRING function cannot be used with memo or BLOB columns.

TRIM

Removes the trailing or leading character, or both, from a string.

TRIM([LEADING|TRAILING|BOTH] [trimmed_char] FROM column_reference)
Description
Use TRIM to delete the leading or trailing character, or both, from a table column or character literal. The TRIM function only deletes characters located in the specified position.
The first parameter indicates the position of the character to be deleted, and has one of the following values:
Value Description
LEADING Deletes the character at the left end of the string.
TRAILING Deletes the character at the right end of the string.
BOTH Deletes the character at both ends of the string.
The trimmed character parameter specifies the character to be deleted, if present. Case-sensitivity is applied for this parameter. To make TRIM case-insensitive, use the UPPER function.
FROM specifies the column or character literal from which to delete the character. The column reference for FROM can be a table column or a character literal.
Example variations:
TRIM syntax Result
TRIM(LEADING "_" FROM "_ABC_") "ABC_"
TRIM(TRAILING "_" FROM "_ABC_") "_ABC"
TRIM(BOTH "_" FROM "_ABC_") "ABC"
TRIM(BOTH "A" FROM "ABC") "BC"
When applied to retrieved data of a SELECT statement, the effect is transient and does not affect stored data. When applied to the update atoms of an UPDATE statement, the effect is persistent and permanently converts the case of the stored values.
Applicability
TRIM can only be used with character columns or literals. To use on values of other data types, the values must first be converted to CHAR using the CAST function.
Note: the TRIM function cannot be used with memo or BLOB columns.

AVG

Returns the average of the values in a specified column or an expression.

AVG([ALL] column_reference | DISTINCT column_reference)
Description
Use AVG to calculate the average value for a numeric column. As an aggregate function, AVG performs its calculation aggregating values in the same column(s) across all rows in a dataset. The dataset may be the entire table, a filtered dataset, or a logical group produced by a GROUP BY clause. Column values of zero are included in the averaging, so values of 1, 2, 3, 0, 0, and 0 result in an average of 1. NULL column values are not counted in the calculation.
SELECT AVG(itemstotal)
FROM orders
ALL returns the average for all rows. When DISTINCT is not specified, ALL is the implied default.
DISTINCT ignores duplicate values when averaging values in the specified column.
AVG returns the average of values in a column or the average of a calculation using a column performed for each row (a calculated field).
SELECT AVG(itemstotal), AVG(itemstotal * 0.0825) AS AverageTax
FROM orders
When used with a GROUP BY clause, AVG calculates one value for each group. This value is the aggregation of the specified column for all rows in each group. The statement below aggregates the average value for the order totals column in the ORDERS table, producing a subtotal for each company in the COMPANY table.
SELECT C."company", AVG(O."itemstotal") AS Average,
MAX(O."itemstotal") AS Biggest,
MIN(O."itemstotal") AS Smallest
FROM "customer.db" C, "orders.db" O
WHERE (C."custno" = O."custno")
GROUP BY C."company"
ORDER BY C."company"
Applicability
AVG operates only on numeric values. To use AVG on non-numeric values, first use the CAST function to convert the column to a numeric type.
Note: the MAX function cannot be used with memo or BLOB columns.

COUNT

Returns the number of rows that satisfy a query’s search condition.

COUNT(* | [ALL] column_reference | DISTINCT column_reference)
Description
Use COUNT to count the number of rows retrieved by a SELECT statement. The SELECT statement may be a single- or multi-table query. The value returned by COUNT reflects a reduced row count produced by a filtered dataset.
SELECT COUNT(amount)
FROM averaging
ALL returns the count for all rows. When DISTINCT is not specified, ALL is the implied default.
DISTINCT ignores duplicate values in the specified column when counting rows.

MAX

Returns the largest value in the specified column.

MAX([ALL] column_reference | DISTINCT column_reference)
Description
Use MAX to calculate the largest value for a numeric column. As an aggregate function, MAX performs its calculation aggregating values in the same column(s) across all rows in a dataset. The dataset may be the entire table, a filtered dataset, or a logical group produced by a GROUP BY clause. Column values of zero are included in the aggregation. NULL column values are not counted in the calculation. If the number of qualifying rows is zero, MAX returns a NULL value.
SELECT MAX(itemstotal)
FROM orders
ALL returns the largest value for all rows. When DISTINCT is not specified, ALL is the implied default.
DISTINCT ignores duplicate values when calculating the largest value in the specified column.
MAX returns the largest value in a column or a calculation using a column performed for each row (a calculated field).
SELECT MAX(itemstotal), MAX(itemstotal * 0.0825) AS HighestTax
FROM orders
When used with a GROUP BY clause, MAX returns one calculation value for each group. This value is the aggregation of the specified column for all rows in each group. The statement below aggregates the largest value for the order totals column in the ORDERS table, producing a subtotal for each company in the COMPANY table.
SELECT C."company", AVG(O."itemstotal") AS Average,
MAX(O."itemstotal") AS Biggest,
MIN(O."itemstotal") AS Smallest
FROM "customer.db" C, "orders.db" O
WHERE (C."custno" = O."custno")
GROUP BY C."company"
ORDER BY C."company"
Applicability
MAX can be used with all non-BLOB columns. When used with numeric columns, the return value is of the same type as the column (such as INTEGER or FLOAT). When used with a CHAR column, the largest value returned will depend on the Borland Database Engine (BDE) language driver used.
Note: the MAX function cannot be used with memo or BLOB columns.

MIN

Returns the smallest value in the specified column.

MIN([ALL] column_reference | DISTINCT column_reference)
Description
Use MIN to calculate the smallest value for a numeric column. As an aggregate function, MIN performs its calculation aggregating values in the same column(s) across all rows in a dataset. The dataset may be the entire table, a filtered dataset, or a logical group produced by a GROUP BY clause. Column values of zero are included in the aggregation. NULL column values are not counted in the calculation. If the number of qualifying rows is zero, MIN returns a NULL value.
SELECT MIN(itemstotal)
FROM orders
ALL returns the smallest value for all rows. When DISTINCT is not specified, ALL is the implied default.
DISTINCT ignores duplicate values when calculating the smallest value in the specified column.
MIN returns the smallest value in a column or a calculation using a column performed for each row (a calculated field).
SELECT MIN(itemstotal), MIN(itemstotal * 0.0825) AS LowestTax
FROM orders
When used with a GROUP BY clause, MIN returns one calculation value for each group. This value is the aggregation of the specified column for all rows in each group. The statement below aggregates the smallest value for the order totals column in the ORDERS table, producing a subtotal for each company in the COMPANY table.
SELECT C."company", AVG(O."itemstotal") AS Average,
MAX(O."itemstotal") AS Biggest,
MIN(O."itemstotal") AS Smallest
FROM "customer.db" C, "orders.db" O
WHERE (C."custno" = O."custno")
GROUP BY C."company"
ORDER BY C."company"
Applicability
MIN can be used with all non-BLOB columns. When used with numeric columns, the return value is of the same type as the column (such as INTEGER or FLOAT). When used with a CHAR column, the smallest value returned will depend on the Borland Database Engine (BDE) language driver used.
Note: the MIN function cannot be used with memo or BLOB columns.

SUM

Calculates the sum of values for a column.

SUM([ALL] column_reference | DISTINCT column_reference)
Description
Use SUM to sum all the values in the specified column. As an aggregate function, SUM performs its calculation aggregating values in the same column(s) across all rows in a dataset. The dataset may be the entire table, a filtered dataset, or a logical group produced by a GROUP BY clause. Column values of zero are included in the aggregation. NULL column values are not counted in the calculation. If the number of qualifying rows is zero, SUM returns a NULL value.
SELECT SUM(itemstotal)
FROM orders
ALL returns the smallest value for all rows. When DISTINCT is not specified, ALL is the implied default.
DISTINCT ignores duplicate values when calculating the smallest value in the specified column.
MIN returns the smallest value in a column or a calculation using a column performed for each row (a calculated field).
SELECT SUM(itemstotal), SUM(itemstotal * 0.0825) AS TotalTax
FROM orders
When used with a GROUP BY clause, SUM returns one calculation value for each group. This value is the aggregation of the specified column for all rows in each group. The statement below aggregates the total value for the order totals column in the ORDERS table, producing a subtotal for each company in the COMPANY table.
SELECT C."company", SUM(O."itemstotal") AS SubTotal
FROM "customer.db" C, "orders.db" O
WHERE (C."custno" = O."custno")
GROUP BY C."company"
ORDER BY C."company"
Applicability
SUM operates only on numeric values. To use SUM on non-numeric values, first use the CAST function to convert the column to a numeric type.

CAST

Converts specified value to the specified data type.

CAST(column_reference AS data_type)
Description
Use CAST to convert the value in the specified column to the data type specified. CAST can also be applied to literal and calculated values. CAST can be used in the columns list of a SELECT statement, in the predicate for a WHERE clause, or to modify the update atom of an UPDATE statement.
The statement below converts a Paradox DATETIME column value to DATE.
SELECT CAST(saledate AS DATE)
FROM ORDERS
Converting a column value with CAST allows use of other functions or predicates on an otherwise incompatible data type, such as using the SUBSTRING function on a DATE column.
SELECT saledate,
SUBSTRING(CAST(CAST(saledate AS DATE) AS CHAR(10)) FROM 1 FOR 1)
FROM orders
When applied to retrieved data of a SELECT statement, the effect is transient and does not affect stored data. When applied to the update atoms of an UPDATE statement, the effect is persistent and permanently converts the case of the stored values.
Note: the CAST function cannot be used with memo or BLOB columns.

EXTRACT

Returns one field from a date value.

EXTRACT (extract_field FROM column_reference)
Description
Use EXTRACT to return the year, month, or day field from a DATE or TIMESTAMP column.
SELECT saledate,
EXTRACT(YEAR FROM saledate) AS YY,
EXTRACT(MONTH FROM saledate) AS MM,
EXTRACT(DAY FROM saledate) AS DD
FROM orders
The statement below uses a DOB column (containing birthdates) to filter to those rows where the date is in the month of May. The month field from the DOB column is retrieved using the EXTRACT function and compared to 5, May being the fifth month.
 
SELECT DOB, LastName, FirstName
FROM People
WHERE (EXTRACT(MONTH FROM DOB) = 5)
Applicability
EXTRACT operates only on DATE, TIME, and TIMESTAMP values. To use EXTRACT on non-date values, first use the CAST function to convert the column to a date type.

ARITHMETIC OPERATORS

Perform arithmetic operations.
numeric_value1 + numeric_value2
numeric_value1 - numeric_value2
numeric_value1 * numeric_value2
numeric_value1 / numeric_value2
Description
Use arithmetic operators to perform arithmetic calculations on data in SELECT queries. Calculations can be performed wherever non-aggregated data values are allowed, such as in a SELECT or WHERE clause. In the statement below, a column value is multiplied by a numeric literal.

SELECT (itemstotal * 0.0825) AS Tax
FROM orders
Arithmetic calculations are performed in the normal order of precedence: multiplication, division, addition, and then subtraction. To cause a calculation to be performed out of the normal order of precedence, use parentheses around the operation to be performed first. In the statement below the addition is performed before the multiplication.
SELECT (n.numbers * (n.multiple + 1)) AS Result
FROM numbertable n
Applicability
Arithmetic operators operate only on numeric values. To use arithmetic operators on non-numeric values, first use the CAST function to convert the column to a numeric type.

LOGICAL OPERATORS

Connect multiple predicates.

[NOT] predicate OR [NOT] predicate
[NOT] predicate AND [NOT] predicate
Description
Use the logical operators OR and AND to connect two predicates in a single WHERE clause. This allows the table to be filtered based on multiple conditions. Logical operators compare the boolean result of two predicate comparisons, each producing a boolean result. If OR is used, either of the two predicate comparisons can result on a TRUE value for the whole expression to evaluate to TRUE. If AND is used, both predicate comparisons must evaluate to TRUE for the whole expression to be TRUE; if either is FALSE, the whole is FALSE. In the statement below, if only one of the two predicate comparisons is TRUE (reservdate < "1/31/1998" or paid = TRUE), the row will be included in the query result set.
SELECT *
FROM reservations
WHERE ((reservdate < "1/31/1998") OR (paid = TRUE))
Logical operator comparisons are performed in the order of precedence: OR and then AND. To perform a comparison out of the normal order of precedence, use parentheses around the comparison to be performed first. The SELECT statement below retrieves all rows where the SHAPE column is "round" and the COLOR "blue". It also returns those rows where the COLOR column is "red", regardless of the value in the SHAPE column (such as "triangle"). It would not return rows where the SHAPE is "round" and the COLOR anything but "blue" or where the COLOR is "blue" and the SHAPE anything but "round".
SELECT shape, color, cost
FROM objects
WHERE ((shape = "round") AND (color = "blue")) OR (color = "red")
Without the parentheses, the default order of precedence is used and the logic changes. The statement below, a variation on the above statement, would return rows where the SHAPE is "square" and the COLOR is "blue". It would also return rows where the SHAPE is "square" and the COLOR is "red". But unlike the preceding statement, it would not return rows where the COLOR is "red" and the SHAPE "triangle".
SELECT shape, color, cost
FROM objects
WHERE shape = "round" AND color = "blue" OR color = "red"
Use the NOT operator to negate the boolean result of a comparison. In the statement below, only those rows where the PAID column contains a FALSE value are retrieved.
SELECT *
FROM reservations
WHERE (NOT (paid = "TRUE"))

COMPARISON

Compare two values.
value1 < value2 less than
value1 > value2 greater than
value1 = value2 equal to
value1 <> value2 not equal to
value1 >= value2 greater than or equal to
value1 <= value2 less than or equal to
Description
Use comparison predicates to compare two like values. Values compared can be: column values, literals, or calculations. The result of the comparison is a boolean value that is used in a WHERE clause to determine on a row-by-row basis whether a row meets the filtering criteria.

SELECT *
FROM orders
WHERE (itemstotal >= 1000)
Comparisons must be between two values of the same or a compatible data type. If one value is of an incompatible data type, convert that value with the CAST function to a compatible data type.

PREDICATE LIST

Local SQL supports the following predicates:
Predicate Description
Comparison Compares two values.

  • BETWEEN Compares a value to a range formed by two values.
  • EXISTS Determines whether a value exists in a look-up table.
  • IN Determines whether a value exists in a list of values or a table.
  • LIKE Compares, in part or in whole, one value with another.
  • IS NULL Compares a value with an empty, or NULL, value.
  • SOME/ANY/ALL Performs quantified comparisons.

BETWEEN

Determines whether a value falls inside a range.

value1 [NOT] BETWEEN value2 AND value3
Description
Use the BETWEEN comparison predicate to compare a value to a value range. If the value is greater than or equal to the low end of the range and less than or equal to the high end of the range, BETWEEN returns a TRUE value. If the value is less than the low end value or greater than the high end value, BETWEEN returns a FALSE value. For example, the expression below returns a FALSE value because 10 is not between 1 and 5.
10 BETWEEN 1 AND 5
Use NOT to return the converse of a BETWEEN comparison. For example, the expression below returns a TRUE value.
10 NOT BETWEEN 1 AND 5
BETWEEN can be used with all non-BLOB data types, but all values compared must be of the same or a compatible data type. If one value is of an incompatible data type, convert that value with the CAST function to a compatible data type. Values used in a BETWEEN comparison may be column, literal, or calculated values.
SELECT saledate
FROM orders
WHERE (saledate BETWEEN "1/1/1988" AND "12/31/1988")
Hint BETWEEN is useful when filtering to retrieve rows with contiguous values that fall within the specified range. For filtering to retrieve rows with noncontiguous values, use the IN predicate.

EXISTS

Indicates whether values exist in a subquery.

EXISTS subquery
Description
Use the EXISTS comparison predicate to filter a table based on the existence of column values from the table in a subquery. The subquery is filtered using a WHERE clause comparing one or more columns in the filtered table to corresponding columns in the subquery. EXISTS returns a true value if the subquery has at least one row in its result set, false if zero rows are retrieved. The subquery is executed once for each row in the filtered table and the existence of rows in the subquery is used to include or exclude the rows in the filtered table.
SELECT O.orderno, O.custno
FROM orders O
WHERE EXISTS
(SELECT C.custno
FROM customer C
WHERE (C.custno = O.custno))
The subquery may be further filtered with other conditions. For example, the statement below returns the rows pertaining to all customers who have placed orders the totals for which exceed $1000.
SELECT C.company, C.custno
FROM customer C
WHERE EXISTS
(SELECT O.custno
FROM orders O
WHERE (O.custno = C.custno) AND (O.itemstotal > 1000))
Use NOT to return the converse of an EXISTS comparison.

IN

Indicates whether a value exists in a set of values.

value [NOT] IN (value_set)
Description
Use the IN comparison predicate to filter a table based on the existence of a column value in a specified set of comparison values. The set of comparison values may be either static using a comma-separated list of literals or dynamic using the result set from a subquery.
The value to compare with the values set can be any or a combination of: a column value, a literal value, or a calculated value.
The comparison set can be a static comma-separated list of literal values.
SELECT C.company, C.state
FROM customer C
WHERE (C.state IN ("CA", "HI"))
The comparison set can also be the result set from a subquery. The subquery may return multiple rows, but must only return a single column for comparison.
SELECT C.company, C.state
FROM customer C
WHERE (C.state IN
(SELECT R.state
FROM regions R
WHERE (R.region = "Pacific")))
Use NOT to return the converse of an IN comparison.
IN can be used with all non-BLOB data types, but all values compared must be of the same or a compatible data type. If one value is of an incompatible data type, convert that value with the CAST function to a compatible data type.
Hint IN is useful when filtering to retrieve rows with noncontiguous values. For filtering to retrieve rows with contiguous values that fall within a specified range, use the BETWEEN predicate.

LIKE

Indicates the similarity of one value as compared to another.

value [NOT] LIKE [substitution_char] comparison_value [substitution_char] [ESCAPE escape_char]
Description
Use the LIKE comparison predicate to filter a table based on the similarity of a column value to a comparison value. Use of substitution characters allows the comparison to be based on the whole column value or just a portion.
SELECT *
FROM customer
WHERE (company LIKE "Adventure Undersea")
The wildcard substitution character ("%") may be used in the comparison to represent an unknown number of characters. LIKE returns a TRUE when the portion of the column value matches that portion of the comparison value not corresponding to the position of the wildcard character. The wildcard character can appear at the beginning, middle, or end of the comparison value (or multiple combinations of these positions). For example, the statement below retrieves rows where the column value begins with "A" and is followed by any number of any characters. Matching values could include ( $_SERVER['DOCUMENT_ROOT']."/includes/Action Club" and "Adventure Undersea", but not "Blue Sports".
SELECT *
FROM customer
WHERE (company LIKE "A%")
The single-character substitution character ("_") may be used in the comparison to represent a single character. LIKE returns a TRUE when the portion of the column value matches that portion of the comparison value not corresponding to the position of the single-character substitution character. The single-character substitution character can appear at the beginning, middle, or end of the comparison value (or multiple combinations of these positions). Use one single-character substitution character for each character to be wild in the filter pattern For example, the statement below retrieves rows where the column value begins with "b" ends with "n", with one character of any value between. Matching values could include ( $_SERVER['DOCUMENT_ROOT']."/includes/bin" and "ban", but not "barn".
SELECT words
FROM dictionary
WHERE (words LIKE "b_n")
Use NOT to return the converse of a LIKE comparison.
Use ESCAPE when the wildcard character "%" or "_" appear as data in the column. The ESCAPE keyword designates an escape character. In the comparison value for the LIKE predicate, the character that follows the escape character is treated as a data character and not a wildcard character. Other wildcard characters in the comparison value are unaffected.
In the example below, the "$" character is designated as the escape character. In the comparison value for the LIKE predicate ("%10$%%"), the "%" that immediately follows the escape character is treated as data in the PercentValue. This allows filtering based on the string "10%".
SELECT *
FROM Sales
WHERE (PercentValue LIKE "%10$%%" ESCAPE "$")
LIKE can be used only with CHAR or compatible data types. If one value is of an incompatible data type, convert that value with the CAST function to a compatible data type. The comparison performed by the LIKE predicate is case-sensitive.

IS NULL

Indicates whether a column contains a NULL value.

column_reference IS [NOT] NULL
Description
Use the IS NULL comparison predicate to filter a table based on the specified column containing a NULL (empty) value.
SELECT *
FROM customer
WHERE (invoicedate IS NULL)
Use NOT to return the converse of a IS NULL comparison.
Note For a numeric column, a zero value is not the same as a NULL value.

SOME/ANY/ALL

Compares a column value to a column value in multiple rows in a subquery.
column_reference comparison_predicate SOME | ANY | ALL (subquery)
Description
Use the quantified comparison predicates SOME, ANY, and ALL to filter a table by comparing a column value with multiple comparison values. The quantified comparison predicates are used with comparison predicates to compare a column value to the multiple values in a column of a subquery.
The ANY predicate evaluates TRUE when the accompanying comparison predicate evaluates TRUE for any value from the subquery. The SOME predicate operates functionally the same as ANY. For example, using the statement below, for any row to be retrieved from the HOLDINGS table, the value in the PUR_PRICE column need only be greater than any one value returned in the subquery’s PRICE column.

SELECT *
FROM "holdings.dbf" H
WHERE (H."pur_price" > ANY
(SELECT O."price"
FROM "old_sales.dbf"))
The ALL predicate evaluates TRUE when the accompanying comparison predicate evaluates TRUE for all values from the subquery. For example, using the statement below, for any row to be retrieved from the HOLDINGS table, the value in the PUR_PRICE column needs to be greater than every value returned in the subquery’s PRICE column.
SELECT *
FROM "holdings.dbf" H
WHERE (H."pur_price" > ALL
(SELECT O."price"
FROM "old_sales.dbf"))
Note The subquery providing the comparison values for the quantified comparison predicates may retrieve multiple rows, but can only have one column.

RELATIONAL OPERATORS LIST

Local SQL supports the following join types:
Join operator Description

  • Equi-join Joins two tables, filtering out non-matching rows.
  • INNER Joins two tables, filtering out non-matching rows.
  • OUTER Joins two tables, retaining non-matching rows.
  • Cartesian Joins two tables, matching each row of one table with each row from the other.
  • UNION Concatenates the result set of one query with the result set of another query.
  • Heterogeneous Joins two tables in different databases, including differing database types.

EQUIJOIN

Joins two tables based on column values common between the two, excluding non-matches.

SELECT column_list
FROM table_reference, table_reference [, table_reference...]
WHERE predicate [AND predicate...]
Description
Use equi-join to join two tables, a source and joining table, that have values from one or more columns in common. One or more columns from each table are compared in the WHERE clause for equal values. For rows in the source table that have a match in the joining table, the data for the source table rows and matching joining table rows are included in the result set. Rows in the source table without matches in the joining table are excluded from the joined result set. In the statement below, the CUSTOMER and ORDERS tables are joined based on values in the CUSTNO column, which each table contains.
SELECT *
FROM customer C, orders O
WHERE (C.custno = O.custno)
More that one table may be joined with an equi-join. One column comparison predicate in the WHERE clause is required for each column compared to join each two tables. The statement below joins the CUSTOMER table to ORDERS, and then ORDERS to ITEMS. In this case, the joining table ORDERS acts as a source table for the joining table ITEMS.
SELECT *
FROM customer C, orders O, items I
WHERE (C.custno = O.custno) AND
(O.orderno = I.orderno)
Tables may also be joined using a concatenation of multiple column values to produce a single value for the join comparison predicate. Here, the ID1 and ID2 columns in JOINING are concatenated and compared with the values in the single column ID in SOURCE.
SELECT *
FROM source S, joining J
WHERE (S.ID = J.ID1 || J.ID2)
An ORDER BY clause in equi-join statements can use columns from any table specified in the FROM clause to sort the result set.

INNER JOIN

Joins two tables based on column values common between the two, excluding non-matches.

SELECT column_list
FROM table_reference
[INNER] JOIN table_reference
ON predicate
[[INNER] JOIN table_reference
ON predicate...]
Description
Use an INNER JOIN to join two tables, a source and joining table, that have values from one or more columns in common. One or more columns from each table are compared in the ON clause for equal values. For rows in the source table that have a match in the joining table, the data for the source table rows and matching joining table rows are included in the result set. Rows in the source table without matches in the joining table are excluded from the joined result set. In the statement below, the CUSTOMER and ORDERS tables are joined based on values in the CUSTNO column, which each table contains.
SELECT *
FROM customer C
INNER JOIN orders O
ON (C.custno = O.custno)
More than one table may be joined with an INNER JOIN. One use of the INNER JOIN operator and corresponding ON clause is required for each each set of two tables joined. One columns comparison predicate in an ON clause is required for each column compared to join each two tables. The statement below joins the CUSTOMER table to ORDERS, and then ORDERS to ITEMS. In this case, the joining table ORDERS acts as a source table for the joining table ITEMS. (The statement below appears without the optional INNER keyword.)
SELECT *
FROM customer C
JOIN orders O
ON (C.custno = O.custno)
JOIN items I
ON (O.orderno = I.orderno)
Tables may also be joined using a concatenation of multiple column values to produce a single value for the join comparison predicate. Here, the ID1 and ID2 columns in JOINING are concatenated and compared with the values in the single column ID in SOURCE.
SELECT *
FROM source S
INNER JOIN joining J
ON (S.ID = J.ID1 || J.ID2)
An ORDER BY clause in INNER JOIN statements can use columns from any table specified in the FROM clause to sort the result set.

OUTER JOIN

Joins two tables based on column values common between the two, including non-matches.

SELECT column_list
FROM table_reference
LEFT | RIGHT | FULL [OUTER] JOIN table_reference
ON predicate
[LEFT | RIGHT | FULL [OUTER] JOIN table_reference
ON predicate...]
Description
Use an OUTER JOIN to join two tables, a source and joining table, that have one or more columns in common. One or more columns from each table are compared in the ON clause for equal values. The primary difference between inner and outer joins is that, in outer joins rows from the source table that do not have a match in the joining table are not excluded from the result set. Columns from the joining table for rows in the source table without matches have NULL values.
In the statement below, the CUSTOMER and ORDERS tables are joined based on values in the CUSTNO column, which each table contains. For rows from CUSTOMER that do not have a matching value between CUSTOMER.CUSTNO and ORDERS.CUSTNO, the columns from ORDERS contain NULL values.
SELECT *
FROM customer C
LEFT OUTER JOIN orders O
ON (C.custno = O.custno)
The LEFT modifier causes all rows from the table on the left of the OUTER JOIN operator to be included in the result set, with or without matches in the table to the right. If there is no matching row from the table on the right, its columns contain NULL values. The RIGHT modifier causes all rows from the table on the right of the OUTER JOIN operator to be included in the result set, with or without matches. If there is no matching row from the table on the left, its columns contain NULL values. The FULL modifier causes all rows from the all tables specified in the FROM clause to be included in the result set, with or without matches. If there is no matching row from one of the tables, its columns contain NULL values.
More than one table may be joined with an INNER JOIN. One use of the INNER JOIN operator and corresponding ON clause is required for each each set of two tables joined. One column comparison predicate in an ON clause is required for each column compared to join each two tables. The statement below joins the CUSTOMER table to ORDERS, and then ORDERS to ITEMS. In this case, the joining table ORDERS acts as a source table for the joining table ITEMS.
SELECT *
FROM customer C
FULL OUTER JOIN orders O
ON (C.custno = O.custno)
FULL OUTER JOIN items I
ON (O.orderno = I.orderno)
Tables may also be joined using expressions to produce a single value for the join comparison predicate. Here, the ID1 and ID2 columns in JOINING are separately compared with two values produced by the SUBSTRING function using the single column ID in SOURCE.
SELECT *
FROM source S
RIGHT OUTER JOIN joining J
ON (SUBSTRING(S.ID FROM 1 FOR 2) = J.ID1) AND
(SUBSTRING(S.ID FROM 3 FOR 1) = J.ID2)
An ORDER BY clause in OUTER JOIN statements can use columns from any table specified in the FROM clause to sort the result set.

CARTESIAN JOIN

Joins two tables in a non-relational manner.

SELECT *
FROM table_reference, table_reference [,table_reference...]
Description
Use the Cartesian join to join the column of two tables into one result set, but without correlation between the rows from the tables. Cartesian joins match each row of the source table with each row of the joining table. No column comparisons are used, just simple association. If the source table has 10 rows and the joining table has 10, the result set will contain 100 rows as each row from the source table is joined with each row from the joined table.
SELECT *
FROM "employee.dbf", "items.db"

UNION JOIN

Concatenates the rows of one table to the end of another table.

SELECT col_1 [, col_2, ... col_n]
FROM table_reference
UNION [ALL]
SELECT col_1 [, col_2, ... col_n]
FROM table_reference
Description
Use the UNION join to add the rows of one table to the end of another similarly structured SELECT query result sets. The SELECT statement for the source and joining tables must include the same number of columns for them to be UNION compatible. The table structures themselve need not be the same as long as those column included in the SELECT statements are.
SELECT custno, company
FROM customers
UNION
SELECT custno, company
FROM old_customers
Matching names and data types is not mandatory for result set columns retrieved by the UNION across the multiple tables. If there is a data type difference between two tables for a given column, the data type of the column in the first SELECT statement in the UNION join is used. Data is translated as best the BDE can for that column from the other tables. For example, if the second column of the first table is SMALLINT and CHAR(10) in the second table, the result set uses SMALLINT. Any data from the second table that cannot be converted from CHAR(10) to SMALLINT becomes zeros. Column name differences are also automatically handled. If the first column of two tables has a different name, the first column in the UNION result set will use that from the first SELECT statement.
By default, non-distinct rows are aggregated into single rows in a UNION join. Use ALL to retain non-distinct rows.
To join two tables with UNION where one table does not have a column included by another, a compatible literal or expression may be used instead in the SELECT statement missing the column. For example, if there is no column in the JOINING table corresponding to the NAME column in SOURCE an expression is used to provide a value for a pseudo JOINING.NAME column. Assuming SOURCE.NAME is of type CHAR(10), the CAST function is used to convert an empty character string to CHAR(10).
SELECT S.id, name
FROM source S
UNION ALL
SELECT J.id, CAST("" AS CHAR(10))
FROM joiner J

HETEROGENEOUS JOIN

Joins two tables from different databases.

SELECT column_list
FROM ":database_reference:table_reference", ":database_reference:table_reference" [,":database_reference:table_reference"...]
WHERE predicate [AND predicate...]
Description
Use a heterogeneous join to join two tables that reside in different databases. The joined tables may be of different types (like dBASE to Paradox or Paradox to InterBase), but you can only join tables whose database types are accessible through the BDE (local, ODBC, or SQL Links). A hetergeneous join may be any of the joins supported by local SQL. The difference is in the syntax for the table reference: the database containing each table is specified in the table reference, surrounded by colons and the whole reference enclosed in quotation marks. The database specified as part of the table reference may be a drive and directory reference (for local tables) or a BDE alias.
SELECT *
FROM ":DBDEMOS:customer.db" C, ":BCDEMOS:orders.db" O
WHERE (C.custno = O.custno)