备注:测试数据库版本为MySQL 8.0
如需要scott用户下建表及录入数据语句，可参考:
scott建表及录入数据sql脚本
问题:
要知道两个表或视图中是否有相同的数据(基数和值)。考虑这个视图
create view v
as
select * from emp where deptno != 10
union all
select * from emp where ename = 'WARD';
select * from v;
mysql> create view v
-> as
-> select * from emp where deptno != 10
-> union all
-> select * from emp where ename = 'WARD';
Query OK, 0 rows affected (0.03 sec)
mysql> select * from v;
+-------+--------+----------+------+------------+---------+---------+--------+
| empno | ename | job | mgr | hiredate | sal | comm | deptno |
+-------+--------+----------+------+------------+---------+---------+--------+
| 7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL | 20 |
| 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 |
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 |
| 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL | 20 |
| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 |
| 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | NULL | 30 |
| 7788 | SCOTT | ANALYST | 7566 | 1987-06-13 | 3000.00 | NULL | 20 |
| 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 |
| 7876 | ADAMS | CLERK | 7788 | 1987-06-13 | 1100.00 | NULL | 20 |
| 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 |
| 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL | 20 |
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 |
+-------+--------+----------+------+------------+---------+---------+--------+
12 rows in set (0.00 sec)
现在要检测这个视图与表EMP中的数据是否完全相同。
员工“WARD”行重复，说明解决方案不仅是要显示不同行，还要显示重复行。
因为在表EMP中部门10中的员工有3行，而对于员工“WARD”来说有2行。
解决方案:
使用关联子查询和union all来查找在视图V中存在而在表EMP中不存在的行。
然后在表EMP中存在而在视图V中不存在的行进行合并:
select *
from (
select e.empno,e.ename,e.job,e.mgr,e.hiredate,e.sal,e.comm,e.deptno,count(*) as cnt
from emp e
group by empno,ename,job,mgr,hiredate,sal,comm,deptno) e
where not exists (
select null
from (
select v.empno,v.ename,v.job,v.mgr,v.hiredate,v.sal,v.comm,v.deptno,count(*) as cnt
from v
group by empno,ename,job,mgr,hiredate,sal,comm,deptno ) v
where v.empno = e.empno
and v.ename = e.ename
and v.job = e.job
and v.mgr = e.mgr
and v.hiredate = e.hiredate
and v.sal = e.sal
and v.deptno = e.deptno
and v.cnt = e.cnt
and coalesce(v.comm,0) = coalesce(v.comm,0)
)
union all
select *
from (
select v.empno,v.ename,v.job,v.mgr,v.hiredate,v.sal,v.comm,v.deptno,count(*) as cnt
from v
group by empno,ename,job,mgr,hiredate,sal,comm,deptno ) v
where not exists (
select null
from (
select e.empno,e.ename,e.job,e.mgr,e.hiredate,e.sal,e.comm,e.deptno,count(*) as cnt
from emp e
group by empno,ename,job,mgr,hiredate,sal,comm,deptno) e
where v.empno = e.empno
and v.ename = e.ename
and v.job = e.job
and v.mgr = e.mgr
and v.hiredate = e.hiredate
and v.sal = e.sal
and v.deptno = e.deptno
and v.cnt = e.cnt
and coalesce(v.comm,0) = coalesce(v.comm,0)
)
执行记录:
mysql> select *
-> from (
-> select e.empno,e.ename,e.job,e.mgr,e.hiredate,e.sal,e.comm,e.deptno,count(*) as cnt
-> from emp e
-> group by empno,ename,job,mgr,hiredate,sal,comm,deptno) e
-> where not exists (
-> select null
-> from (
-> select v.empno,v.ename,v.job,v.mgr,v.hiredate,v.sal,v.comm,v.deptno,count(*) as cnt
-> from v
-> group by empno,ename,job,mgr,hiredate,sal,comm,deptno ) v
-> where v.empno = e.empno
-> and v.ename = e.ename
-> and v.job = e.job
-> and v.mgr = e.mgr
-> and v.hiredate = e.hiredate
-> and v.sal = e.sal
-> and v.deptno = e.deptno
-> and v.cnt = e.cnt
-> and coalesce(v.comm,0) = coalesce(v.comm,0)
-> )
-> union all
-> select *
-> from (
-> select v.empno,v.ename,v.job,v.mgr,v.hiredate,v.sal,v.comm,v.deptno,count(*) as cnt
-> from v
-> group by empno,ename,job,mgr,hiredate,sal,comm,deptno ) v
-> where not exists (
-> select null
-> from (
-> select e.empno,e.ename,e.job,e.mgr,e.hiredate,e.sal,e.comm,e.deptno,count(*) as cnt
-> from emp e
-> group by empno,ename,job,mgr,hiredate,sal,comm,deptno) e
-> where v.empno = e.empno
-> and v.ename = e.ename
-> and v.job = e.job
-> and v.mgr = e.mgr
-> and v.hiredate = e.hiredate
-> and v.sal = e.sal
-> and v.deptno = e.deptno
-> and v.cnt = e.cnt
-> and coalesce(v.comm,0) = coalesce(v.comm,0)
-> )
-> ;
+-------+--------+-----------+------+------------+---------+--------+--------+-----+
| empno | ename | job | mgr | hiredate | sal | comm | deptno | cnt |
+-------+--------+-----------+------+------------+---------+--------+--------+-----+
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 | 1 |
| 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | NULL | 10 | 1 |
| 7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 | 1 |
| 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 | 1 |
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 | 2 |
+-------+--------+-----------+------+------------+---------+--------+--------+-----+
5 rows in set (0.00 sec)