子查询

---IN---

select * from foo where id in (select max(id) from foo );

select * from foo where id NOT in (select max(id) from foo );

 

---EXISTS---

select * from foo where EXISTS (select 语句，次语句如果查询到值括号为true，否则括号内的值为false);

-->此关键字（EXISTS）后面的查询（我意思说后面括号内的查询）会返回一个值，记作val

    如果val为空，前面的查询不执行

    如果val不为空，前面的查询执行

selecgt * from foo where NOT EXISTS(select....);

 

---ANY---

select * from t1 where col_x > ANY (select col_y from t2);

-->外查询大于任意子查询的所有记录被取出

 

---ALL---

select * from t1 where col_x > ALL(select col_y from t2);

-->外查询大于所有子查询记录的记录被取出

 

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