SQL Language Enhancements

Caution

EXECUTE STATEMENT is potentially unsafe in several ways:

1.There is no way to validate the syntax of the enclosed statement.

2.There are no dependency checks to discover whether tables or columns have been dropped.

3.Operations will be slow because the embedded statement has to be prepared every time it is executed.

4.Return values are strictly checked for data type in order to avoid unpredictable type-casting exceptions. For example, the string '1234' would convert to an integer, 1234, but 'abc' would give a conversion error.

5.If the stored procedure has special privileges on some objects, the dynamic statement submitted in the EXECUTE STATEMENT string does not inherit them. Privileges are restricted to those granted to the user who is executing the procedure.

(1.5) New Context Variables

Dmitry Yemanov

A number of new context variables for PSQL have been implemented.

CURRENT_CONNECTION and CURRENT_TRANSACTION

These context variables return the system identifier of the active connection or the current transaction context, respectively. Return type is INTEGER. Available in DSQL and PSQL.

Important

Because these values are stored on the database header page, they will be reset after a database restore.

Syntax Patterns

CURRENT_CONNECTION

CURRENT_TRANSACTION

Examples

SELECT CURRENT_CONNECTION FROM RDB$DATABASE;

NEW.TXN_ID = CURRENT_TRANSACTION;

EXECUTE PROCEDURE P_LOGIN(CURRENT_CONNECTION);

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SQL Language Enhancements

ROW_COUNT

Returns an integer, the number of rows affected by the last DML statement. Available in PSQL, in the context of the procedure or trigger module.

Currently returns zero from a SELECT statement.

Syntax Pattern

ROW_COUNT

Examples

UPDATE TABLE1 SET FIELD1 = 0 WHERE ID = :ID;

IF (ROW_COUNT = 0) THEN

INSERT INTO TABLE1 (ID, FIELD1) VALUES (:ID, 0);

Note

ROW_COUNT cannot be used for checking the rows affected by an EXECUTE STATEMENT command.

SQLCODE and GDSCODE

Each context variable returns an integer which is the numeric error code for the active exception. Available in PSQL, within the scope of the particular exception handling block. Both will evaluate to zero outside the block.

The GDSCODE variable returns a numeric representation of the GDS (ISC) error code, e.g. '335544349L' will return 335544349.

A 'WHEN SQLCODE' or 'WHEN ANY' exception block will catch a non-zero value for the SQLCODE variable and return zero for GDSCODE. Only a 'WHEN GDSCODE' block can catch a non-zero GDSCODE variable (and will return zero in SQLCODE).

If a user-defined exception is thrown, both SQLCODE and GDSCODE variables contain zero, regardless of the exception handling block type.

Syntax Pattern

SQLCODE

GDSCODE

Example

BEGIN

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