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MySQL数据库优化概述四_MySQL

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Release: 2016-06-01 13:59:50
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table type   possible_keys key     key_len ref           rows Extra


tt    ALL    AssignedPC    NULL    NULL    NULL          3872 Using
             ClientID,                                        where
             ActualPC
et    eq_ref PRIMARY       PRIMARY 15      tt.ActualPC   1
et_1  eq_ref PRIMARY       PRIMARY 15      tt.AssignedPC 1
do    eq_ref PRIMARY       PRIMARY 15      tt.ClientID   1


  请注意,EXPLAIN 结果中的 rows 字段的值也是MySQL的连接优化程序大致猜测的,请检查这个值跟真实值是否基本一致。如果不是,可以通过在 SELECT 语句中使用 STRAIGHT_JOIN 来取得更好的性能,同时可以试着在 FROM

  分句中用不同的次序列出各个表

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