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MySQL stored procedure, handling multiple cursors and query results

Asked 2010-01-03T14:55:50.800
10

How can I use two cursors in the same routine? If I remove the second cursor declaration and fetch loop everthing works fine. The routine is used for adding a friend in my webapp. It takes the id of the current user and the email of the friend we want to add as a friend, then it checks if the email has a corresponding user id and if no friend relation exists it will create one. Any other routine solution than this one would be great as well.

DROP PROCEDURE IF EXISTS addNewFriend;
DELIMITER //
CREATE PROCEDURE addNewFriend(IN inUserId INT UNSIGNED, IN inFriendEmail VARCHAR(80))
BEGIN
    DECLARE tempFriendId INT UNSIGNED DEFAULT 0;
    DECLARE tempId INT UNSIGNED DEFAULT 0;
    DECLARE done INT DEFAULT 0;

    DECLARE cur CURSOR FOR
        SELECT id FROM users WHERE email = inFriendEmail;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

    OPEN cur;
    REPEAT
        FETCH cur INTO tempFriendId;
    UNTIL done  = 1 END REPEAT;
    CLOSE cur;

    DECLARE cur CURSOR FOR 
        SELECT user_id FROM users_friends WHERE user_id = tempFriendId OR friend_id = tempFriendId;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

    OPEN cur;
    REPEAT
        FETCH cur INTO tempId;
    UNTIL done  = 1 END REPEAT;
    CLOSE cur;

    IF tempFriendId != 0 AND tempId != 0 THEN
        INSERT INTO users_friends (user_id, friend_id) VALUES(inUserId, tempFriendId);
    END IF;
    SELECT tempFriendId as friendId;
END //
DELIMITER ;
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1 Answer

4

I know you found a better solution, but I believe the answer to your original question is that you need to SET Done=0; between the two cursors, otherwise the second cursor will only fetch one record before exiting the loop due to Done=1 from the previous handler.

answered 2010-06-03T14:12:13.613

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