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I have a very complex MySQL query that includes use of the same subquery three times. Will MySQL actually run the subquery three times? (It's an expensive one.) If so, is there a way for me to tell MySQL to save or cache the results so it won't do that? I could save the data in a large array then re-feed it to MySQL, but I'd rather not move it out and back into the database like that.

This is the subquery that appears three times:

SELECT id FROM programs 
WHERE submitter_id=32 AND id in (
    SELECT id FROM programs 
    WHERE feed_id=2478 AND id in (
        SELECT program_id FROM playlist_program_map 
        WHERE playlist_id=181)))

And here's an example of the full query in which the query appears:

SELECT object_id, programs.created AS created, 
MATCH(text) AGAINST ('excellent ' IN BOOLEAN MODE) AS relevance 
FROM comments_programs USE INDEX (text) 
LEFT JOIN programs ON programs.id=object_id 
WHERE object_id IN (
    SELECT id FROM programs 
    WHERE 1 AND id IN (
        SELECT id FROM programs 
        WHERE submitter_id=32 AND id in (
            SELECT id FROM programs 
            WHERE feed_id=2478 AND id in (
                SELECT program_id FROM playlist_program_map 
                WHERE playlist_id=181)))) 
AND MATCH(text) AGAINST ('excellent ' IN BOOLEAN MODE)>0)

UNION (

SELECT object_id, programs.created AS created, 
MATCH(text) AGAINST ('excellent ' IN BOOLEAN MODE) AS relevance 
FROM descriptions_programs USE INDEX (text) 
LEFT JOIN programs ON programs.id=object_id 
WHERE object_id IN (
    SELECT id FROM programs 
    WHERE 1 AND id IN (
        SELECT id FROM programs 
        WHERE submitter_id=32 AND id in (
            SELECT id FROM programs 
            WHERE feed_id=2478 AND id in (
                SELECT program_id FROM playlist_program_map 
                WHERE playlist_id=181)))) 
AND MATCH(text) AGAINST ('excellent ' IN BOOLEAN MODE)>0 AND current=1 ) 

UNION (

SELECT object_id, programs.created AS created, 
MATCH(text) AGAINST ('excellent ' IN BOOLEAN MODE) AS relevance 
FROM titles_programs USE INDEX (text) 
LEFT JOIN programs ON programs.id=object_id 
WHERE object_id IN (
    SELECT id FROM programs 
    WHERE 1 AND id IN (
        SELECT id FROM programs 
        WHERE submitter_id=32 AND id in (
            SELECT id FROM programs 
            WHERE feed_id=2478 AND id in (
                SELECT program_id FROM playlist_program_map 
                WHERE playlist_id=181)))) 
AND MATCH(text) AGAINST ('excellent ' IN BOOLEAN MODE)>0 AND current=1;
4

2 に答える 2

0

何らかの理由で、サブセレクトを含む mysql IN 句の実行が非常に遅くなります。join を使用することをお勧めします。サブクエリは次のようになります。

プログラムから ID を選択 P1 INNER JOIN プログラム P2 ON P1.id = P2.id INNER JOIN プレイリスト_program_map PMAP ON P2.id = PMAP.program_id WHERE P1.submitter_id=32 AND P2.feed_id=2478 AND PMAP.playlist_id=181

それははるかに速く実行されます。

于 2012-03-09T01:21:17.683 に答える