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MySQL winter vacation self-study 2022 11 (8)
2022-07-06 02:25:00 【Crane paper thousand】
-- Query whether the company has more than 60 Year old employees , Output if there is
select * from emp3 where exists(select * from emp3 where age > 60);# Wrong writing , Output for the whole table
select * from emp3 a where exists(select * from emp3 b where a.age > 60);
select * from emp3 where eid in (select eid from emp3 where age > 60);# use in To achieve
-- Query the employee information of the Department
select * from emp3 a where exists (select * from dept3 b where a.dept_id = b.deptno);
select * from emp3 a where dept_id in(select deptno from dept3 );# use in To achieve
Be careful exists Efficiency currency of in high
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