Reuse SQL Server cursor with different parameter value? - sql-server

Question

I wonder whether cursor for query with #variable parameter can be re-used (CLOSE + OPEN) when value of the #variable changes. To me it looks that it always needs CLOSE + DEALLOCATE + DECLARE + OPEN to take new value of the #variable into effect. Perhaps no big deal, but I wanted to know whether DEALLOCATE + DECLARE can be left out between uses.
Here you have complete simple example to try it out:
DECLARE #ta TABLE (a int);
INSERT INTO #ta (a) VALUES (1),(2),(4),(8),(16),(32),(64);
---------
DECLARE #current_a int;
DECLARE #threshold int = 12;
DECLARE crs1 CURSOR FOR SELECT a FROM #ta WHERE a < #threshold;
--- first cursor use
OPEN crs1;
FETCH NEXT FROM crs1 INTO #current_a;
WHILE ##FETCH_STATUS = 0
BEGIN
SELECT #threshold, #current_a
FETCH NEXT FROM crs1 INTO #current_a;
END;
CLOSE crs1;
DEALLOCATE crs1; -- can this be left out?
SET #threshold = 3;
DECLARE crs1 CURSOR FOR SELECT a FROM #ta WHERE a < #threshold; -- can this be left out?
--- second cursor use
OPEN crs1;
FETCH NEXT FROM crs1 INTO #current_a;
WHILE ##FETCH_STATUS = 0
BEGIN
SELECT #threshold, #current_a
FETCH NEXT FROM crs1 INTO #current_a;
END;
CLOSE crs1;
DEALLOCATE crs1;
This was linearized example, but the question applies also to nested cursors when outer cursor changes the query parameter of inner cursor.

Answer 1

One way is to use cursor variable:
DECLARE
{
{ #local_variable [AS] data_type | [ = value ] }
| { #cursor_variable_name CURSOR }
#cursor_variable_name
Is the name of a cursor variable. Cursor variable names must begin with an at (#) sign and conform to the rules for identifiers.
CURSOR
Specifies that the variable is a local cursor variable.
A cursor variable:
Can be the target of either a cursor type or another cursor variable. For more information, see SET #local_variable.
Can be referenced as the target of an output cursor parameter in an EXECUTE statement if the cursor variable does not have a cursor
currently assigned to it.
Should be regarded as a pointer to the cursor.
DECLARE crs1 CURSOR FOR SELECT a FROM #ta WHERE a < #threshold;
-- could be changed to
DECLARE #crs1 CURSOR;
SET #crs1 = CURSOR FOR SELECT a FROM #ta WHERE a < #threshold;
LiveDemo