oracle+in改exists,in, not in, exists, not exists, join 改写
create or replace view v1 as select ename,job,sal from emp where deptno = 30;
create or replace view v2 as select ename,job,sal from emp;
-- 查找两个表中匹配的行
/*使用内连接*/
select v1.* from v1,v2 where v1.ename=v2.ename and v1.job=v2.job and v1.sal=v2.sal
/*使用半连接*/
select * from v1 where (ename,job,sal) in (select ename,job,sal from v2)
/*使用intersect函数*/
SQL> select * from v2
2 intersect
3 select * from v1;
ENAME JOB SAL
---------- --------- ----------
ALLEN SALESMAN 1600
BLAKE MANAGER 2850
JAMES CLERK 950
MARTIN SALESMAN 1250
TURNER SALESMAN 1500
WARD SALESMAN 1250
6 rows selected.
-- 查找两个表中不匹配的行
/*使用半连接，使用not in需要注意null值的问题*/
SQL> select * from v2 where (ename,job,sal) not in (select ename,job,sal from v1);
ENAME JOB SAL
---------- --------- ----------
SMITH CLERK 800
JONES MANAGER 2975
CLARK MANAGER 2450
SCOTT ANALYST 3000
KING PRESIDENT 5000
ADAMS CLERK 1100
FORD ANALYST 3000
MILLER CLERK 1300
8 rows selected.
/* 使用minus函数, 注意表的先后顺序 */
SQL> select * from v2 minus select * from v1;
ENAME JOB SAL
---------- --------- ----------
ADAMS CLERK 1100
CLARK MANAGER 2450
FORD ANALYST 3000
JONES MANAGER 2975
KING PRESIDENT 5000
MILLER CLERK 1300
SCOTT ANALYST 3000
SMITH CLERK 800
8 rows selected.
/* 使用not in 的空值处理 */
create table emp1 (deptno number);
insert into emp1 values (10);
insert into emp1 values (20);
insert into emp1 values (50);
insert into emp1 values (null);
/* 下面查询返回结果为空 */
SQL> select deptno from dept where deptno not in (select deptno from emp1);
no rows selected
/* 解决方法一：添加is not null 条件 */
SQL> select deptno from dept where deptno not in (select deptno from emp1 where deptno is not null);
DEPTNO
----------
30
40
/* 解决方法二：使用相关连子查询,下面两个语句可以使用左外连接改写，见最后 */
SQL> select deptno from dept where not exists (select null from emp1 where dept.deptno=emp1.deptno);
DEPTNO
----------
30
40
SQL> select deptno from dept where deptno not in (select deptno from emp1 where emp1.deptno=dept.deptno);
DEPTNO
----------
30
40
/* 解决方法三：在字段上添加非空约束,这个需要根据实际业务需求处理 */
/* 返回dept在emp表中不匹配的记录，要求返回部门的所有信息 */
SQL> select * from dept where deptno not in (select deptno from emp where deptno is not null);
DEPTNO DNAME LOC
---------- -------------- -------------
40 OPERATIONS BOSTON
/* 上面的反连接可以使用做外连接改写 */
SQL> select dept.* from dept left join emp on dept.deptno=emp.deptno where emp.deptno is null;
DEPTNO DNAME LOC
---------- -------------- -------------
40 OPERATIONS BOSTON
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