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  • 一道题来对mysql的连接查询复习

    题目如上,下面是我按照上面的表字段自己建的表

    car

    customer

    employee

    sale

    下面是对第四问的的解答,用的是mysql 的连接查询,可能方法有点麻烦。

    我的想法很简单,这个查询针对多个表,我就把需要查询的结果一个个的先做简单查询,最后再进行组合。

    第一步:从sale和car表中查出每个员工的销售额:

    SELECT sale.EMPnum,SUM((sale.CARnum*car.Cprice)) AS money  FROM sale,car WHERE sale.CARnum=car.Cid GROUP BY EMPnum;#从sale和car表中查出每个员工的
    

    第二步:查询每个员工的销售数量:

    SELECT EMPnum,COUNT(EMPnum) AS num FROM sale GROUP BY EMPnum;#查询每个员工的销售数量  
    

    第三步:查询员工的名称:  

    SELECT Eid,Ename FROM Employee;#查询员工的名字
    

    第四步:将第一步和第二步的结果做为这次查询的表,查询每个员工的销售额和销售数量:

    SELECT t1.EMPnum,t1.money,t2.num FROM (SELECT sale.EMPnum,SUM((sale.CARnum*car.Cprice)) AS money  FROM sale,car WHERE sale.CARnum=car.Cid GROUP BY EMPnum) AS t1 ,(SELECT EMPnum,COUNT(EMPnum) AS num FROM sale GROUP BY EMPnum) AS t2 WHERE t1.EMPnum=t2.EMPnum;
    

     第五步:将第四步的结果和第三步的结果做为这步的查询表,查询最后的结果

    SELECT t3.EMPnum,t3.money,t3.num,t4.Ename FROM (SELECT t1.EMPnum,t1.money,t2.num FROM (SELECT sale.EMPnum,SUM((sale.CARnum*car.Cprice)) AS money  FROM sale,car WHERE sale.CARnum=car.Cid GROUP BY EMPnum) AS t1 ,(SELECT EMPnum,COUNT(EMPnum) AS num FROM sale GROUP BY EMPnum) AS t2 WHERE t1.EMPnum=t2.EMPnum) AS t3,(SELECT Eid,Ename FROM Employee) AS t4 WHERE t3.EMPnum=t4.Eid;
    

      

      

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  • 原文地址:https://www.cnblogs.com/Jc-zhu/p/4971990.html
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