13.6.6 Cursors

MySQL supports cursors inside stored programs. The syntax is as in embedded SQL. Cursors have these properties:

Asensitive: The server may or may not make a copy of its result table
Read only: Not updatable
Nonscrollable: Can be traversed only in one direction and cannot skip rows

Cursor declarations must appear before handler declarations and after variable and condition declarations.

Example:

CREATE PROCEDURE curdemo()
BEGIN
DECLARE done INT DEFAULT FALSE;
DECLARE a CHAR(16);
DECLARE b, c INT;
DECLARE cur1 CURSOR FOR SELECT id,data FROM test.t1;
DECLARE cur2 CURSOR FOR SELECT i FROM test.t2;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
OPEN cur1;
OPEN cur2;
read_loop: LOOP
FETCH cur1 INTO a, b;
FETCH cur2 INTO c;
IF done THEN
LEAVE read_loop;
END IF;
IF b < c THEN
INSERT INTO test.t3 VALUES (a,b);
ELSE
INSERT INTO test.t3 VALUES (a,c);
END IF;
END LOOP;
CLOSE cur1;
CLOSE cur2;
END;

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Document created the 26/06/2006, last modified the 26/10/2018
Source of the printed document:https://www.gaudry.be/en/mysql-rf-cursors.html

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References

Manuel MySQL : https://dev.mysql.com/

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