SQL基础之多表连接查询

有三个表：T_USER， t_group， T_USER_GROUP

1.select* from T_USER

2.select * from t_groupd

3.select * from T_USER_GROUP

1./*所有职员中最高最低分查询*/select username from T_USER where bonus>600select max(bonus) as 最高分,min(bonus) as 最低分 from T_USER select count(*) as 优秀 from T_USER where bonus>=500

2./*所有职员的平均奖金*/select AVG(bonus) as "所有人的平均奖金" from T_USER

3./*各部门平均奖金*/select t_group.groupname as "部门", AVG(T_USER.bonus) AS "平均奖金" from t_group left join T_USER_GROUP on t_group.groupid = T_USER_GROUP.groupidleft join T_USER on T_USER_GROUP.userid = T_USER.userid group by t_group.groupname;

4./*各部门里面奖金大于平均值的职员*/select a.groupid, a.groupname,a.username,a.bonus from (select t_group.groupid, t_group.groupname,T_USER.username,T_USER.bonus from t_group left join T_USER_GROUP on t_group.groupid = T_USER_GROUP.groupid left join T_USER on  T_USER.userid = T_USER_GROUP.userid) a left join (select t_group.groupid,t_group.groupname, AVG(T_USER.bonus) AS avgbonus from t_group left join T_USER_GROUP on t_group.groupid = T_USER_GROUP.groupidleft join T_USER on T_USER_GROUP.userid = T_USER.userid group by t_group.groupid,t_group.groupname) b on a.groupid=b.groupidwhere a.bonus>b.avgbonus

5./*各部门里奖金最高（低）的面前三名*/SELECT  t1.*FROM    (select t_group.groupid,T_USER.userid,T_USER.username,t_group.groupname,T_USER.bonus from T_USER_GROUP LEFT JOIN T_USER ON T_USER.userid = T_USER_GROUP.userid LEFT JOIN t_group ON t_group.groupid = T_USER_GROUP.groupid) t1WHERE   t1.userid IN ( SELECT TOP 3                            t2.userid                     FROM   (select t_group.groupid,T_USER.username,T_USER.userid,t_group.groupname,T_USER.bonus from T_USER_GROUP LEFT JOIN T_USER ON T_USER.userid = T_USER_GROUP.userid LEFT JOIN t_group ON t_group.groupid = T_USER_GROUP.groupid) t2                     WHERE  t2.groupid = t1.groupid                     ORDER BY t2.bonus ASC )                     ORDER BY t1.groupid DESC ,t1.bonus asc

6./*部门平均奖金<400*/ select * from (select t_group.groupid as "部门编号",t_group.groupname as "部门名字", AVG(T_USER.bonus) AS "平均奖金" from t_group left join T_USER_GROUP on t_group.groupid = T_USER_GROUP.groupidleft join T_USER on T_USER_GROUP.userid = T_USER.userid group by t_group.groupid,t_group.groupname) bwhere  "平均奖金"<400

7./*部门平均奖金小于所有人的平均奖金*/select b.*from (select t_group.groupname as "部门", AVG(T_USER.bonus) AS "平均奖金" from t_group left join T_USER_GROUP on t_group.groupid = T_USER_GROUP.groupidleft join T_USER on T_USER_GROUP.userid = T_USER.userid group by t_group.groupname) b join (select t_group.groupname as "部门",AVG(T_USER.bonus) as "所有人平均奖金" from T_USER,t_group  group by t_group.groupid,t_group.groupname) a on b.部门=a.部门where b.平均奖金<a.所有人平均奖金

8.

/*求平均奖金小于总平均奖金的部门里面的最高和最低奖金步骤*//*第一步所有员工的平均奖金*/select AVG(bonus) from T_USER/*第二步求各部门的平均奖金*/select b.groupid,AVG(a.bonus) as avgbonus from T_USER a left join T_USER_GROUP b on a.userid=b.useridgroup by groupid/*第三步求平均值小于总平均值的部门*/select s.groupid from(select b.groupid,AVG(a.bonus) as avgbonus from T_USER a left join T_USER_GROUP b on a.userid=b.useridgroup by groupid)swhere s.avgbonus<(select AVG(bonus) from T_USER)/*第四步求平均值小于总平均值的部门里面的人员的groupid,userid,username,bonus*/select tug.groupid,tu.userid,tu.username,tu.bonus from(select s.groupid from(select b.groupid,AVG(a.bonus) as avgbonus from T_USER a left join T_USER_GROUP b on a.userid=b.useridgroup by groupid)swhere s.avgbonus<(select AVG(bonus) from T_USER)) p inner join T_USER_GROUP tug on tug.groupid=p.groupidinner join T_USER tu on tu.userid=tug.userid /*第五步将第三步得到表的信息存储到虚拟表w中*/select f.groupid,f.userid,f.username,f.bonus  into w from(select tug.groupid,tu.userid,tu.username,tu.bonus from(select s.groupid from(select b.groupid,AVG(a.bonus) as avgbonus from T_USER a left join T_USER_GROUP b on a.userid=b.useridgroup by groupid)swhere s.avgbonus<(select AVG(bonus) from T_USER)) p inner join T_USER_GROUP tug on tug.groupid=p.groupidinner join T_USER tu on tu.userid=tug.userid )f/*最后查询平均奖金小于总平均值的部门里面的最高和最低奖金获得者的信息*/select tr.userid,tr.username,k.maxbonus from (select groupid,min(bonus) as maxbonus from wgroup by groupid)kinner join T_USER_GROUP tup on tup.groupid=k.groupidinner join T_USER tr on tr.userid=tup.userid and tr.bonus=k.maxbonus

9.

/*查询姓名id为1的职工所在的部门和奖金*/select T_USER.userid, t_group.groupid,groupname,bonus from T_USERinner join T_USER_GROUP on T_USER.userid=T_USER_GROUP.useridinner join t_group on T_USER_GROUP.groupid=t_group.groupidwhere T_USER.userid=1

10.

/*查询生产部门里面奖金大于500的人员的信息，并按照高到低排序*/select a.groupid,b.userid,username,groupname,bonus from t_group aleft join T_USER_GROUP b on a.groupid=b.groupidleft join T_USER c on b.userid=c.useridwhere groupname='生产部' and bonus>500order by bonus desc

11.

/*查询id号在8-25之间的职员的所有信息*/select groupname,username,bonus from T_USERinner join T_USER_GROUP on T_USER.userid=T_USER_GROUP.useridinner join t_group on t_group.groupid=T_USER_GROUP.groupidwhere T_USER.userid>8 and T_USER.userid<25

 将min换成max就是求最高奖金，本例子上午关键之处是派生表的灵活运用，例子中的a,b,f,t up ,tr，w,k等都是派生表，灵活使用派生表是数据库中很重要的一个技能，我也还在学习阶段