MySQL之子查询

匿名 (未验证) 提交于 2019-12-02 22:02:20
create table emp (id int,name char(10),sex char,age int,dept_id int,job char(10),salary double);  insert into emp values (1,"刘备","男",26,1,"总监",5800), (2,"张飞","男",24,1,"员工",3000), (3,"关羽","男",30,1,"员工",4000), (4,"孙权","男",25,2,"总监",6000), (5,"周瑜","男",22,2,"员工",5000), (6,"小乔","女",31,2,"员工",4000), (7,"曹操","男",19,3,"总监",10000), (8,"司马懿","男",24,3,"员工",6000);  create table dept(id int primary key,name char(10)); insert into dept values(1,"市场"),(2,"行政"),(3,"财务");

首先明确子查询就是一个普通的查询,当一个查询需要作为子查询使用时,用括号包裹即可

exists后跟子查询,子查询有结果是为True,没有结果时为False。为True时外层执行,为False外层不执行

select from emp where exists (select from emp where salary > 1000);

前面 exists 后面
如果 后面 查询有结果时,前面 才会执行

标签
易学教程内所有资源均来自网络或用户发布的内容,如有违反法律规定的内容欢迎反馈
该文章没有解决你所遇到的问题?点击提问,说说你的问题,让更多的人一起探讨吧!