Question

我有一个包含以下表格的数据库

german_akkusativ_plural [ akkusativ_plural, word_id ]
german_akkusativ_singular [ akkusativ_singular, word_id ]
german_dativ_plural [ dativ_plural, word_id ]
german_dativ_singular [ dativ_singular, word_id ]
german_gender [ gender, word_id ]
german_genitiv_plural [ genitiv_plural, word_id ]
german_genitiv_singular [ genitiv_singular, word_id ]
german_nominativ_plural [ nominativ_plural, word_id ]
german_nominativ_singular [ nominativ_singular, word_id ]
german_word [ id, word, blacklisted ]

以及下面的查询应该找到一个单词的相应性别（该单词可以在任何一个案例中）

SELECT gg.gender
    FROM german_word gw
        INNER JOIN 
            german_nominativ_singular gns
            ON gw.id = gns.word_id
        INNER JOIN 
            german_nominativ_plural gnp
            ON gw.id = gnp.word_id
        INNER JOIN 
            german_akkusativ_singular gas
            ON gw.id = gas.word_id
        INNER JOIN 
            german_akkusativ_plural gap
            ON gw.id = gap.word_id
        INNER JOIN 
            german_dativ_singular gds
            ON gw.id = gds.word_id
        INNER JOIN 
            german_dativ_plural gdp
            ON gw.id = gdp.word_id
        INNER JOIN 
            german_genitiv_singular ggs
            ON gw.id = ggs.word_id
        INNER JOIN 
            german_genitiv_plural ggp
            ON gw.id = ggp.word_id
        INNER JOIN 
            german_gender gg
            ON gw.id = gg.word_id
    WHERE 
        gns.nominativ_singular = 'Auto' OR
        gnp.nominativ_plural = 'Auto' OR
        gas.akkusativ_singular = 'Auto' OR
        gap.akkusativ_plural = 'Auto' OR
        gds.dativ_singular = 'Auto' OR
        gdp.dativ_plural = 'Auto' OR
        ggs.genitiv_singular = 'Auto' OR
        ggp.genitiv_plural = 'Auto'

问题是当我在phpMyAdmin中运行查询时，运行需要大约150秒。这是为什么？除了'黑名单'之外，我在所有字段上都有索引。

这是正确的方法，还是我完全偏离轨道？

我非常感谢任何帮助！感谢。

编辑：

这是EXPLAIN的输出

id  select_type table   type    possible_keys               key     key_len ref                         rows    Extra
1   SIMPLE      gg      ALL     word_id                     NULL    NULL    NULL                        41522   
1   SIMPLE      gdp     ref     dativ_plural,word_id        word_id 5       usr_web410_3.gg.word_id     1       Using where
1   SIMPLE      ggp     ref     genitiv_plural,word_id      word_id 5       usr_web410_3.gg.word_id     1       Using where
1   SIMPLE      gap     ref     akkusativ_plural,word_id    word_id 5       usr_web410_3.gg.word_id     1       Using where
1   SIMPLE      gnp     ref     nominativ_plural,word_id    word_id 5       usr_web410_3.ggp.word_id    1       Using where
1   SIMPLE      gas     ref     akkusativ_singular,word_id  word_id 5       usr_web410_3.gg.word_id     1       Using where
1   SIMPLE      gns     ref     nominativ_singular,word_id  word_id 5       usr_web410_3.gg.word_id     1       Using where
1   SIMPLE      gds     ref     dativ_singular,word_id      word_id 5       usr_web410_3.gns.word_id    1       Using where
1   SIMPLE      ggs     ref     genitiv_singular,word_id    word_id 5       usr_web410_3.gg.word_id     1       Using where
1   SIMPLE      gw      eq_ref  PRIMARY                     PRIMARY 4       usr_web410_3.gg.word_id     1       Using index

Answer 1

您正在获取每个表中的每一行，然后检查是否有任何表匹配'Auto'。这很慢。这些OR对性能不利，所以你必须放弃它们。

有很多方法可以重写您的查询，我只会建议一个。首先，我认为没有理由使用german_word表。它不存在于where或select子句中，因此我们可以使用german_gender表。请记住，更大的SQL查询并不一定意味着性能更差。

试试这个。它应该更快地带来相同的结果。我假设所有文本列都像nominativ_singular一样被编入索引。

SELECT gg.gender as gender
FROM german_gender gg
    INNER JOIN german_nominativ_singular gns
    ON gg.word_id = gns.word_id AND gns.nominativ_singular = 'Auto'
UNION  
SELECT gg.gender as gender
FROM german_gender gg
    INNER JOIN german_nominativ_plural gnp
    ON gg.word_id = gnp.word_id AND gnp.nominativ_plural = 'Auto' 
UNION  
SELECT gg.gender as gender
FROM german_gender gg
    INNER JOIN german_akkusativ_singular gas
    ON gg.word_id = gas.word_id AND gas.akkusativ_singular = 'Auto' 
UNION  
SELECT gg.gender as gender
FROM german_gender gg
    INNER JOIN german_akkusativ_plural gap
    ON gg.word_id = gap.word_id AND gap.akkusativ_plural = 'Auto' 
UNION  
SELECT gg.gender as gender
FROM german_gender gg
    INNER JOIN german_dativ_singular gds
    ON gg.word_id = gds.word_id AND gds.dativ_singular = 'Auto' 
UNION  
SELECT gg.gender as gender
FROM german_gender gg
    INNER JOIN german_dativ_plural gdp
    ON gg.word_id = gdp.word_id AND gdp.dativ_plural = 'Auto' 
UNION  
SELECT gg.gender as gender
FROM german_gender gg
    INNER JOIN german_genitiv_singular ggs
    ON gg.word_id = ggs.word_id AND ggs.genitiv_singular = 'Auto' 
UNION  
SELECT gg.gender as gender
FROM german_gender gg
    INNER JOIN german_genitiv_plural ggp
    ON gg.word_id = ggp.word_id AND ggp.genitiv_plural = 'Auto'

MySQL查询时间为153秒，我做错了什么？

1 个答案: