MySQL LEFT JOINS порядок, как понять правильный алгоритм - PullRequest
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MySQL LEFT JOINS порядок, как понять правильный алгоритм

0 голосов
/ 29 сентября 2018

Я действительно сбит с толку о том, каков правильный порядок написания ЛЕВЫХ СОЕДИНЕНИЙ, на самом деле, если я переместил одно ЛЕВОЕ СОЕДИНЕНИЕ из позиции А в Z, запрос будет в 3 раза быстрее, но ПОЧЕМУ?Почему оптимизатор сам по себе не получает правильный порядок?

Как понять, какой правильный порядок написания запроса с N LEFT JOINS?

Пример:

ЗАМЕДЛЕННЫЙ ЗАПРОС: 

  SELECT
    c.idRichiesta, i.idImmobile
FROM anagrafica AS cli
INNER JOIN richieste AS c  ON c.idCliente = cli.idCliente
INNER JOIN cat_richieste AS cr ON cr.idRichiesta = c.idRichiesta
LEFT JOIN (
    SELECT tmr.* FROM (
        (
            SELECT idRichiesta, id_comune, id_frazione, id_nazione
            FROM comuni_richieste
            WHERE idRichiesta = '129563'
        )
        UNION ALL
        (
            SELECT mr.idRichiesta, m.id_comune, m.id_frazione, m.id_nazione
            FROM macro_aree_richieste AS mr
            INNER JOIN macro_aree_dettaglio AS m ON m.id_macro=mr.id_macro
            WHERE mr.idRichiesta = '129563'
        )
    ) AS tmr
    GROUP BY tmr.idRichiesta, tmr.id_comune, tmr.id_frazione
) AS tcr ON tcr.idRichiesta = c.idRichiesta
LEFT JOIN richieste_coordinate_p AS tcrp ON tcrp.idRichiesta = c.idRichiesta
LEFT JOIN richieste_coordinate_c AS tcrc ON tcrc.idRichiesta = c.idRichiesta
INNER JOIN immobili i on i.idCategoria = cr.idCategoria
LEFT JOIN loc_geo as Ltg on Ltg.idImmobile = i.idImmobile
LEFT JOIN stato_mediazione AS s  ON s.id=i.stato_mediazione
WHERE
    i.proposta_in_corso!='2'
    AND (
        (
            (i.Motivazione = 'Vendita')
            AND (  i.Prezzo_Richiesto >= ( c.Prezzo_Min * (100 - 30)/100 ) )
            AND (( ( i.Prezzo_Richiesto * (100 - 30)/100 ) <= ( c.Prezzo_Max * (100 + 30)/100 ) ) or c.Prezzo_Max = 0 )
        )
        OR
        (
            (i.Motivazione ='Affitto/Vendita')
            AND (
                (( i.Prezzo_Richiesto2 >= ( c.Prezzo_Min  * (100 - 30)/100 )) AND ((( i.Prezzo_Richiesto2 * (100 - 30)/100 )  <= ( c.Prezzo_Max * (100 + 30)/100) ) or c.Prezzo_Max=0) AND c.Motivo_Richiesta ='Affitto')
                OR
                (( i.Prezzo_Richiesto >= ( c.Prezzo_Min  * (100 - 30)/100 )) AND ((( i.Prezzo_Richiesto * (100 - 30)/100 )  <= ( c.Prezzo_Max * (100 + 30)/100) ) or c.Prezzo_Max=0)  AND c.Motivo_Richiesta ='Acquisto')
            )
        )
    )
    AND (
        ( i.Citta = tcr.id_comune  AND ((i.ZonaCitta=tcr.id_frazione) OR (tcr.id_frazione = 0) ) )
        OR (
            Ltg.latitudine is not null and Ltg.longitudine is not null
            AND ( tcrp.poligono is not null AND
                ( ST_CONTAINS(tcrp.poligono, POINT(Ltg.latitudine, Ltg.longitudine)) )
                OR ( tcrc.centro is not null AND
                    round (((acos( sin(( X(tcrc.centro) * 0.0174532925)) * sin((Ltg.latitudine * 0.0174532925)) + cos(( X(tcrc.centro) * 0.0174532925)) * cos((Ltg.latitudine * 0.0174532925)) * cos((( Y(tcrc.centro) - Ltg.longitudine) * 0.0174532925)))) * 57.2957795131) * 111.18957696, 2) <= (tcrc.raggio / 1000)
                )
            )
        )
    )
    AND i.Citta>0
    AND (c.idRichiesta = '129563')
    AND (s.id IS NULL OR s.vendibile='si')

GROUP BY i.idImmobile

ОБЪЯСНЕНИЕ 

+------+--------------+------------------+--------+-------------------------------------------------------+-------------+---------+---------------------------------------+------+---------------------------------+--+
|  id  | select_type  |      table       |  type  |                     possible_keys                     |     key     | key_len |                  ref                  | rows |              Extra              |  |
+------+--------------+------------------+--------+-------------------------------------------------------+-------------+---------+---------------------------------------+------+---------------------------------+--+
| 1    | PRIMARY      | tcrp             | system | idRichiesta                                           | NULL        | NULL    | NULL                                  | 0    | const row not found             |  |
| 1    | PRIMARY      | tcrc             | system | idRichiesta                                           | NULL        | NULL    | NULL                                  | 0    | const row not found             |  |
| 1    | PRIMARY      | c                | const  | PRIMARY,idCliente,Prezzo_Max,Motivo_Richiesta         | PRIMARY     | 4       | const                                 | 1    | Using temporary; Using filesort |  |
| 1    | PRIMARY      | cli              | const  | PRIMARY                                               | PRIMARY     | 4       | const                                 | 1    | Using index                     |  |
| 1    | PRIMARY      | <derived2>       | ref    | <auto_key1>                                           | <auto_key1> | 4       | const                                 | 0    | Using where                     |  |
| 1    | PRIMARY      | cr               | ref    | idRichiesta,idCategoria                               | idRichiesta | 4       | const                                 | 9    | Using index condition           |  |
| 1    | PRIMARY      | i                | ref    | PRIMARY,idProprietario,id_cantiere,codice_agenzia,... | idCategoria | 5       | test_import2.cr.idCategoria     | 2780 | Using where                     |  |
| 1    | PRIMARY      | Ltg              | ref    | idImmobile                                            | idImmobile  | 4       | test_import2.i.idImmobile       | 1    | Using where                     |  |
| 1    | PRIMARY      | s                | eq_ref | PRIMARY                                               | PRIMARY     | 4       | test_import2.i.stato_mediazione | 1    | Using where                     |  |
| 2    | DERIVED      | <derived3>       | ALL    | NULL                                                  | NULL        | NULL    | NULL                                  | 9    | Using temporary; Using filesort |  |
| 3    | DERIVED      | comuni_richieste | ref    | idRichiesta                                           | idRichiesta | 4       | const                                 | 7    | NULL                            |  |
| 4    | UNION        | mr               | ref    | idRichiesta,id_macro                                  | idRichiesta | 4       | const                                 | 1    | NULL                            |  |
| 4    | UNION        | m                | ref    | id_macro                                              | id_macro    | 4       | test_import2.mr.id_macro        | 1    | NULL                            |  |
| NULL | UNION RESULT | <union3,4>       | ALL    | NULL                                                  | NULL        | NULL    | NULL                                  | NULL | Using temporary                 |  |
+------+--------------+------------------+--------+-------------------------------------------------------+-------------+---------+---------------------------------------+------+---------------------------------+--+

БЫСТРЫЙ ЗАПРОС : 

     SELECT
    c.idRichiesta, i.idImmobile
FROM anagrafica AS cli
INNER JOIN richieste AS c  ON c.idCliente = cli.idCliente
INNER JOIN cat_richieste AS cr ON cr.idRichiesta = c.idRichiesta

LEFT JOIN richieste_coordinate_p AS tcrp ON tcrp.idRichiesta = c.idRichiesta
LEFT JOIN richieste_coordinate_c AS tcrc ON tcrc.idRichiesta = c.idRichiesta
INNER JOIN immobili i on i.idCategoria = cr.idCategoria
LEFT JOIN loc_geo as Ltg on Ltg.idImmobile = i.idImmobile
LEFT JOIN stato_mediazione AS s  ON s.id=i.stato_mediazione
LEFT JOIN (
    SELECT tmr.* FROM (
        (
            SELECT idRichiesta, id_comune, id_frazione, id_nazione
            FROM comuni_richieste
            WHERE idRichiesta = '129563'
        )
        UNION ALL
        (
            SELECT mr.idRichiesta, m.id_comune, m.id_frazione, m.id_nazione
            FROM macro_aree_richieste AS mr
            INNER JOIN macro_aree_dettaglio AS m ON m.id_macro=mr.id_macro
            WHERE mr.idRichiesta = '129563'
        )
    ) AS tmr
    GROUP BY tmr.idRichiesta, tmr.id_comune, tmr.id_frazione
) AS tcr ON tcr.idRichiesta = c.idRichiesta
WHERE
    i.proposta_in_corso!='2'
    AND (
        (
            (i.Motivazione = 'Vendita')
            AND (  i.Prezzo_Richiesto >= ( c.Prezzo_Min * (100 - 30)/100 ) )
            AND (( ( i.Prezzo_Richiesto * (100 - 30)/100 ) <= ( c.Prezzo_Max * (100 + 30)/100 ) ) or c.Prezzo_Max = 0 )
        )
        OR
        (
            (i.Motivazione ='Affitto/Vendita')
            AND (
                (( i.Prezzo_Richiesto2 >= ( c.Prezzo_Min  * (100 - 30)/100 )) AND ((( i.Prezzo_Richiesto2 * (100 - 30)/100 )  <= ( c.Prezzo_Max * (100 + 30)/100) ) or c.Prezzo_Max=0) AND c.Motivo_Richiesta ='Affitto')
                OR
                (( i.Prezzo_Richiesto >= ( c.Prezzo_Min  * (100 - 30)/100 )) AND ((( i.Prezzo_Richiesto * (100 - 30)/100 )  <= ( c.Prezzo_Max * (100 + 30)/100) ) or c.Prezzo_Max=0)  AND c.Motivo_Richiesta ='Acquisto')
            )
        )
    )
    AND (
        ( i.Citta = tcr.id_comune  AND ((i.ZonaCitta=tcr.id_frazione) OR (tcr.id_frazione = 0) ) )
        OR (
            Ltg.latitudine is not null and Ltg.longitudine is not null
            AND ( tcrp.poligono is not null AND
                ( ST_CONTAINS(tcrp.poligono, POINT(Ltg.latitudine, Ltg.longitudine)) )
                OR ( tcrc.centro is not null AND
                    round (((acos( sin(( X(tcrc.centro) * 0.0174532925)) * sin((Ltg.latitudine * 0.0174532925)) + cos(( X(tcrc.centro) * 0.0174532925)) * cos((Ltg.latitudine * 0.0174532925)) * cos((( Y(tcrc.centro) - Ltg.longitudine) * 0.0174532925)))) * 57.2957795131) * 111.18957696, 2) <= (tcrc.raggio / 1000)
                )
            )
        )
    )
    AND i.Citta>0
    AND (c.idRichiesta = '129563')
    AND (s.id IS NULL OR s.vendibile='si')

GROUP BY i.idImmobile

EXPLAIN 

+------+--------------+------------------+--------+-------------------------------------------------------+-------------+---------+---------------------------------------+------+---------------------------------+--+
|  id  | select_type  |      table       |  type  |                     possible_keys                     |     key     | key_len |                  ref                  | rows |              Extra              |  |
+------+--------------+------------------+--------+-------------------------------------------------------+-------------+---------+---------------------------------------+------+---------------------------------+--+
| 1    | PRIMARY      | tcrp             | system | idRichiesta                                           | NULL        | NULL    | NULL                                  | 0    | const row not found             |  |
| 1    | PRIMARY      | tcrc             | system | idRichiesta                                           | NULL        | NULL    | NULL                                  | 0    | const row not found             |  |
| 1    | PRIMARY      | c                | const  | PRIMARY,idCliente,Prezzo_Max,Motivo_Richiesta         | PRIMARY     | 4       | const                                 | 1    | Using temporary; Using filesort |  |
| 1    | PRIMARY      | cli              | const  | PRIMARY                                               | PRIMARY     | 4       | const                                 | 1    | Using index                     |  |
| 1    | PRIMARY      | cr               | ref    | idRichiesta,idCategoria                               | idRichiesta | 4       | const                                 | 9    | Using index condition           |  |
| 1    | PRIMARY      | i                | ref    | PRIMARY,idProprietario,id_cantiere,codice_agenzia,... | idCategoria | 5       | test_import2.cr.idCategoria     | 2780 | Using where                     |  |
| 1    | PRIMARY      | Ltg              | ref    | idImmobile                                            | idImmobile  | 4       | test_import2.i.idImmobile       | 1    | NULL                            |  |
| 1    | PRIMARY      | s                | eq_ref | PRIMARY                                               | PRIMARY     | 4       | test_import2.i.stato_mediazione | 1    | Using where                     |  |
| 1    | PRIMARY      | <derived2>       | ref    | <auto_key1>                                           | <auto_key1> | 4       | test_import2.cr.idRichiesta     | 0    | Using where                     |  |
| 2    | DERIVED      | <derived3>       | ALL    | NULL                                                  | NULL        | NULL    | NULL                                  | 9    | Using temporary; Using filesort |  |
| 3    | DERIVED      | comuni_richieste | ref    | idRichiesta                                           | idRichiesta | 4       | const                                 | 7    | NULL                            |  |
| 4    | UNION        | mr               | ref    | idRichiesta,id_macro                                  | idRichiesta | 4       | const                                 | 1    | NULL                            |  |
| 4    | UNION        | m                | ref    | id_macro                                              | id_macro    | 4       | test_import2.mr.id_macro        | 1    | NULL                            |  |
| NULL | UNION RESULT | <union3,4>       | ALL    | NULL                                                  | NULL        | NULL    | NULL                                  | NULL | Using temporary                 |  |
+------+--------------+------------------+--------+-------------------------------------------------------+-------------+---------+---------------------------------------+------+---------------------------------+--+

Как вы можете видеть, единственная разница - это позиция LEFT JOIN с производным запросом.Но почему второй быстрее первого?Как это можно увидеть в выводе EXPLAIN?

Не стесняйтесь спрашивать меня, что вам нужно (индексный список, создание таблицы и т. Д.).Спасибо всем.

1 Ответ

0 голосов
/ 04 октября 2018

Какую версию вы используете?Более новые версии материализуют производные таблицы и находят подходящий для них индекс, как указано <auto_key1>.Это иногда является преимуществом производительности.Старые версии просто повторят выполнение SELECT (и UNION, в вашем случае) каждый раз, когда оно достигает LEFT JOIN.

Не используйте LEFT, если вам это не нужно.Убедитесь, что вы хотите материал после LEFT, даже если строки отсутствуют.(Еще падение LEFT.)

ORs плохо оптимизировать.Посмотри, сможешь ли ты избавиться от них.

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