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Supported SQL Syntax and Functions

This appendix contains the following sections:.

• Supported SQL Statements

• Oracle Functions

Supported SQL Statements

With a few exceptions, the gateway provides full support for Oracle DELETE, INSERT, SELECT, and UPDATE statements.

The gateway does not support Oracle Data Definition Language (DDL) statements. No form of the Oracle ALTER, CREATE, DROP, GRANT, or TRUNCATE statements can be used. Instead, use the pass-through feature of the gateway if you need to use DDL statements against the Microsoft SQL Server database.

See Also: "Using the Pass-Through Feature" and Oracle8i SQL Reference for a detailed descriptions of keywords, parameters, and options.

DELETE

The DELETE statement is fully supported. However, only Oracle functions supported by Microsoft SQL Server can be used.

See Also: "Functions Supported by Microsoft SQL Server" for a list of supported functions.

INSERT

The INSERT statement is fully supported. However, only Oracle functions supported by Microsoft SQL Server can be used.

See Also: "Functions Supported by Microsoft SQL Server" for a list of supported functions.

SELECT

The SELECT statement is fully supported with these exceptions:

• CONNECT BY condition

• FOR UPDATE

• FOR UPDATE OF

• NOWAIT

• START WITH condition

• WHERE CURRENT OF

UPDATE

The UPDATE statement is fully supported. However, only Oracle functions supported by Microsoft SQL Server can be used.

See Also: "Functions Supported by Microsoft SQL Server" for a list of supported functions.

Oracle Functions

All functions are evaluated by the Microsoft SQL Server database after the gateway has converted them to Microsoft SQL Server equivalents. The exception is the TO_DATE function, which is evaluated by the gateway.

Functions Not Supported by Microsoft SQL Server

Oracle SQL functions with no equivalent function in Microsoft SQL Server are not supported in DELETE, INSERT, or UPDATE statements, but are evaluated by the Oracle database server if the statement is a SELECT statement. That is, the Oracle database server performs post-processing of SELECT statements sent to the gateway.

If an unsupported function is used in a DELETE, INSERT, or UPDATE, statement, the following Oracle error occurs:

ORA-02070: database db_link_name does not support function in this context

Functions Supported by Microsoft SQL Server

The gateway translates the following Oracle database server functions in SQL statements to their equivalent Microsoft SQL Server functions:

• Arithmetic Operators

• Comparison Operators

• Pattern Matching

• String Functions

• Group Functions

• Other Functions

Arithmetic Operators

Oracle	Microsoft SQL Server
+	+
-	-
*	*
/	/

Comparison Operators

Oracle	Microsoft SQL Server
=	=
>	>
<	<
>=	>=
<=	<=
<>, !=, ^=	<>
IS NOT NULL	IS NOT NULL
IS NULL	IS NULL

Pattern Matching

Oracle	Microsoft SQL Server
LIKE	LIKE
NOT LIKE	NOT LIKE

String Functions

Oracle	Microsoft SQL Server
||, CONCAT	+ (expression1 + expression2)
ASCII	ASCII
CHR	CHAR
INSTR (with 2 arguments)	CHARINDEX
LENGTH	DATALENGTH
LOWER	LOWER
SUBSTR (second argument cannot be a negative number)	SUBSTRING
UPPER	UPPER

Group Functions

Oracle	Microsoft SQL Server
AVG	AVG
COUNT	COUNT
MAX	MAX
MIN	MIN
SUM	SUM

Other Functions

Oracle	Microsoft SQL Server
ABS	ABS
CEIL	CEILING
COS	COS
EXP	EXP
FLOOR	FLOOR
LN	LOG
LOG	LOG10
MOD	%
NOT NVL	IS NOT NULL
NVL	IS NULL
POWER	POWER
ROUND	ROUND
SIN	SIN
SQRT	SQRT
TAN	TAN

Functions Supported by the Gateway

If an Oracle function has no equivalent function in Microsoft SQL Server, the Oracle function is not translated into the SQL statement and must be post-processed if the SQL statement is a SELECT.

The gateway, however, does support the TO_DATE function equivalent in Microsoft SQL Server, as follows:

TO_DATE(date_string | date_column)

where:

date_string is converted to a string with the following format:

yyyy-mm-dd hh:mi:ss.fff

Recommendation: Supply the date string with the same format as the result (that is, yyyy-mm-dd hh:mi:ss.fff).

date_column is a column with a date data type. It is converted to a parameter with a timestamp data type.