База данных / IS_to_STUD / Soft / 2.1.0.17798-Final / Firebird-2.1.0.17798-0_Win32 / doc / sql.extensions / README.context_variables

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System context variables
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CURRENT_CONNECTION / CURRENT_TRANSACTION (FB 1.5)
-------------------------------------------------

Function:
Returns system identifier of the active connection/transaction,
i.e. a connection/transaction, in which context the given SQL
statement is executed.

Author:
Dmitry Yemanov <yemanov@yandex.ru>

Syntax rules:
CURRENT_CONNECTION / CURRENT_TRANSACTION

Type:
INTEGER

Scope:
DSQL, PSQL

Example(s):
1. SELECT CURRENT_CONNECTION FROM RDB$DATABASE;
2. NEW.CONN_ID = CURRENT_TRANSACTION;
3. EXECUTE PROCEDURE P_LOGIN(CURRENT_CONNECTION);

Note(s):
These values are stored on the database header page,
so they will be reset after a database restore.


ROW_COUNT (FB 1.5)
------------------

Function:
Returns number of rows, affected by the last SQL statement.

Author:
Dmitry Yemanov <yemanov@yandex.ru>

Syntax rules:
ROW_COUNT

Type:
INTEGER

Scope:
PSQL, context of the given procedure/trigger.

Example(s):
UPDATE TABLE1 SET FIELD1 = 0 WHERE ID = :ID;
IF (ROW_COUNT = 0) THEN
INSERT INTO TABLE1 (ID, FIELD1) VALUES (:ID, 0);

Note(s):
1. It can be used to check whether a SELECT statement returned
any rows or not. Also it can be used to exit a fetch loop
on an explicit PSQL cursor.
2. ROW_COUNT contains zero after EXECUTE STATEMENT call. That's
a design limitation, because dynamic SQL statements are
executed as nested requests (i.e. in another context).

See also:
README.cursors


SQLCODE / GDSCODE (FB 1.5)
--------------------------

Function:
Returns numeric error code for the active exception.

Author:
Dmitry Yemanov <yemanov@yandex.ru>

Syntax rules:
SQLCODE / GDSCODE

Type:
INTEGER

Scope:
PSQL, context of the exception handling block.

Example(s):
BEGIN
...
WHEN SQLCODE -802 DO
EXCEPTION E_EXCEPTION_1;
WHEN SQLCODE -803 DO
EXCEPTION E_EXCEPTION_2;
WHEN ANY DO
EXECUTE PROCEDURE P_ANY_EXCEPTION(SQLCODE);
END

Note(s):
1. GDSCODE variable returns a numeric representation of the
appropriate Firebird error code.
2. Both SQLCODE and GDSCODE always evaluate to zero outside
the exception handling block.
3. If you catch exceptions with 'WHEN SQLCODE' block, then only
SQLCODE variable contains the error code inside this block,
whilst GDSCODE contains zero. Obviously, this situation is
opposite for 'WHEN GDSCODE' block.
4. For 'WHEN ANY' block, the error code is set in SQLCODE
variable only.
5. If user-defined exception is thrown, both SQLCODE and GDSCODE
variables contain zero, regardless of the exception handling
block type.

See also:
README.exception_handling


INSERTING / UPDATING / DELETING (FB 1.5)
----------------------------------------

Function:
Determines type of row operation being executed.

Author:
Dmitry Yemanov <yemanov@yandex.ru>

Syntax rules:
INSERTING / UPDATING / DELETING

Type:
BOOLEAN (emulated via pseudo-expression in FB 1.5)

Scope:
PSQL, triggers only.

Example(s):
IF (INSERTING OR DELETING) THEN
NEW.ID = GEN_ID(G_GENERATOR_1, 1);

See also:
README.universal_triggers