Question

I have the following query:

SELECT script FROM d_stages WHERE id IN
(SELECT g.stage + :i FROM games g INNER JOIN sessions s ON
g.expired = 0 AND s.user = g.user AND s.token = :token)

1. Inner SELECT looks for a user id in ‘sessions’ table by a given token, then for a non-expired game for that user.
2. It returns the game stage, which is modified (incremented, decremented, or left with no modification, depending on :i value).
3. Outer SELECT returns a unique script for the found stage from dictionary.

Obviously, the modified stage number (g.stage + :i) should be written back to the DB, since the game has evolved. I can replace SELECT script with SELECT script, g.stage + :i, and use the modified number in another (UPDATE) query, but maybe I can do the same within a single query?

My DBMS is mySQL 5.5.

Regards,

Answer 1

I think, there is only one way:

CREATE DEFINER=`root`@`localhost` PROCEDURE `goto_stage`(IN `inc` INT, IN `session_token` VARCHAR(64))
    LANGUAGE SQL
    NOT DETERMINISTIC
    MODIFIES SQL DATA
    SQL SECURITY DEFINER
    COMMENT ''
BEGIN
    DECLARE new_stage INT;
    SELECT g.stage + inc INTO new_stage FROM games g INNER JOIN sessions s ON
            g.expired = 0 AND s.user = g.user AND s.token = session_token;
    UPDATE games SET stage = new_stage;
    SELECT script FROM d_stages WHERE id = new_stage;
END