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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 Informix 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 Informix can be used. Also, you cannot have SQL statements in the subquery that refer to the same table name in the outer query.

See Also: "Functions Supported by Informix" for a list of supported functions.

INSERT

The INSERT statement is fully supported. However, only Oracle functions supported by Informix can be used. Also, you cannot have SQL statements in the subquery that refer to the same table name in the outer query.

See Also: "Functions Supported by Informix" 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

• Subquery in HAVING clause

UPDATE

The UPDATE statement is fully supported. However, only Oracle functions supported by Informix can be used. Also, you cannot have SQL statements in the subquery that refer to the same table name in the outer query. Subqueries are not supported in the SET clause. Informix does not support table aliases in UPDATE.

See Also: "Functions Supported by Informix" for a list of supported functions.

Oracle Functions

All functions are evaluated by the Informix database after the gateway has converted them to Informix SQL.

Functions Not Supported by Informix

Oracle SQL functions with no equivalent function in Informix 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 Informix

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

• Arithmetic Operators

• Comparison Operators

• String Functions

• Group Functions

• Pattern Matches

• Date Functions

• Other Functions

Arithmetic Operators

Oracle	Informix
+	+
-	-
*	*
/	/

Comparison Operators

Oracle	Informix
=	=
>	>
<	<
>=	>=
<=	<=
<>, !=, ^=	<>
IS NULL	IS NULL
IS NOT NULL	IS NOT NULL

String Functions

Oracle	Informix
||, CONCAT	||
ASCII	ASCII
CHR	CHR
LENGTH	LENGTH

Group Functions

Oracle	Informix
AVG	AVG
COUNT	COUNT
MAX	MAX
MIN	MIN
SUM	SUM

Pattern Matches

Oracle	Informix
LIKE 'a%'	LIKE "a%"
LIKE 'a_'	LIKE "a_"
LIKE 'a\%' ESCAPE '\'	LIKE "a\%" ESCAPE "\"
NOT LIKE	NOT LIKE

Date Functions

Oracle	Informix
date + number	date + number
date - number	date - number
date + date	date + date
date - date	date - date

Other Functions

Oracle	Informix
ABS	ABS
COS	COS
EXP	EXP
LOG10	LOG10
LN	LOGN
LTRIM(char)	TRIM(LEADING FROM char)
MOD	MOD
POWER (m,n)	POW(m,n)
RTRIM(char)	TRIM(TRAILING FROM char)
ROUND (with 1 argument)	ROUND
SIN	SIN
SQRT	SQRT
TAN	TAN
TRUNC (with 1 argument)	TRUNC

Functions Supported by the Gateway

If the Oracle function has no equivalent function in Informix, 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 one function even though there is no equivalent in Informix. This function is the TO_DATE function:

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.