Mysql执行计划--select type

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创建一张tb_student表用于之后测试，主键是id，加上name，score字段

CREATE TABLE `tb_student` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) NOT NULL,
  `score` int(11) NOT NULL,
  PRIMARY KEY (`id`)
)

以下是测试sql，感觉把sql放在一起看比较容易理解

select type	解释	测试sql
simple	简单的select	select * from tb_student
primary	需要union或者子查询	select (select name from tb_student where id =1) from tb_student
union	union操作	select * from tb_student union select * from tb_student
dependent union	查询与外部相关（mysql优化器会将in优化成exists）	select * from tb_student where id in(select id from tb_student union select id from tb_student) select * from tb_student a where EXISTS (select 1 from tb_student where id = a.id union select id from tb_student where id = a.id)
union result	union结果集	select * from tb_student union select * from tb_student
subquery	除了from包含的子查询	select (select name from tb_student where id =1) from tb_student
depend subquery	类似depend union	select (select name from test.tb_student a where a.id=b.id) from test.tb_student b
derived	派生表	select * from (select * from tb_student) t