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PSQL cursors
------------
Function:
Allows explicit cursor operations.
Author:
Dmitry Yemanov <dimitr@users.sf.net>
Syntax rules:
DECLARE [VARIABLE] <cursor_name> [SCROLL | NO SCROLL] CURSOR FOR ( <select_statement> );
OPEN <cursor_name>;
FETCH <cursor_name> [INTO <var_name> [, <var_name> ...]];
FETCH {NEXT | PRIOR | FIRST | LAST | ABSOLUTE <n> | RELATIVE <n>} FROM <cursor_name> [INTO <var_name> [, <var_name> ...]];
CLOSE <cursor_name>;
Example(s):
1. DECLARE RNAME CHAR(31);
DECLARE C CURSOR FOR ( SELECT RDB$RELATION_NAME
FROM RDB$RELATIONS );
BEGIN
OPEN C;
WHILE (1 = 1) DO
BEGIN
FETCH C INTO :RNAME;
IF (ROW_COUNT = 0) THEN
LEAVE;
SUSPEND;
END
CLOSE C;
END
2. DECLARE RNAME CHAR(31);
DECLARE FNAME CHAR(31);
DECLARE C CURSOR FOR ( SELECT RDB$FIELD_NAME
FROM RDB$RELATION_FIELDS
WHERE RDB$RELATION_NAME = :RNAME
ORDER BY RDB$FIELD_POSITION );
BEGIN
FOR
SELECT RDB$RELATION_NAME
FROM RDB$RELATIONS
INTO :RNAME
DO
BEGIN
OPEN C;
FETCH C INTO :FNAME;
CLOSE C;
SUSPEND;
END
END
Note(s):
1. Cursor declaration is allowed only in the beginning of a PSQL block/procedure/trigger
(like a regular local variable declaration).
2. Cursor names are required to be unique in the given context. They cannot interfere
with FOR SELECT cursor (declared via the AS CURSOR clause) names. But a cursor can
share its name with any variable in this context, as possible operations are different.
3. Positioned updates and deletes with cursors using the WHERE CURRENT OF clause are allowed.
4. Attempts to fetch from or close a FOR SELECT cursor are prohibited.
5. Attempts to open cursor which is already open, as well as to fetch from or close cursor
which is already closed, will fail.
6. All cursors which were not explicitly closed will be closed automatically on exit of
the current PSQL block/procedure/trigger.
7. ROW_COUNT system variable can be used to check whether the last FETCH statement returned
any row.
See also:
README.context_variables
README.cursor_variables.txt