mysql面试题索引Mysql---索引命中
sql数据库创建学生表
1、假设 test_demo表中有个复合索引 idx(sex,company,job)
    1.1、最左前缀原则
explain select * from test_demo where sex='' and job ='' and  company=''
结果：type：ref、key：idx
explain select * from test_demo where job ='' and sex='' and  company=''
结果：type：ref、key：idx
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explain select * from test_demo where company='' and job ='' and sex=''
结果：type：ref、key：idx
explain select * from test_demo where job ='' and  company=''
结果：type：all
explain select * from test_demo where company='' and job=''
结果：type：all
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explain select * from test_demo where sex='' and job =''
结果：type：ref、key：idx
explain select * from test_demo where sex='' and company =''
结果：type：ref、key：idx
少儿编程免费视频explain select * from test_demo where sex=''
结果：type：ref、key:idx
explain select * from test_demo where job =''
结果：type：all
explain select * from test_demo where company =''
结果：type：all
    1.2、like不会命中索引spring过滤器
explain select * from test_demo where sex like '%%'
结果：type:all
    1.3、or命中索引
explain select * from test_demo where sex='' or sex =''
结果:type : ref、key：idx
    1.4、负向条件不会命中索引
explain select * from test_demo where sex!=''
结果：type:all
explain select * from test_demo where sex<>''
结果：type:all

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