跪求！跪求！优化,该怎么解决

跪求！！！跪求！！！优化
查询入职最早和最晚的员工名称及入职时间

SQL code

/*1.1*/select e.ename,e.hiredate from emp ewhere e.hiredate=(select min(hiredate) from emp)union allselect e.ename,e.hiredate from emp ewhere e.hiredate=(select max(hiredate) from emp);

 

【点评】：结果数据正确，但同一张表请求了四次，效率需提升，再考虑下

修改：union all改为in

SQL code

select e.ename,e.hiredate from emp ewhere e.hiredate in ((select min(hiredate) from emp),(select max(hiredate) from emp));

【二次点评】：结果数据正确，但还是请求了3次，在效率上还有提升空间




跪求优化


[解决办法]

SQL code

SELECT ENAME, T.HIREDATE  FROM EMP T WHERE NOT EXISTS (SELECT 1 FROM EMP T1 WHERE T1.HIREDATE < T.HIREDATE)    OR NOT EXISTS (SELECT 1 FROM EMP T1 WHERE T1.HIREDATE > T.HIREDATE) 

 

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