SQL> select * from emp;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- ---------- ---------- -------------- ---------- ---------- ----------
7369 SMITH CLERK 7902 17-12月-80 800 20
7499 ALLEN SALESMAN 7698 20-2月 -81 1600 300 30
7521 WARD SALESMAN 7698 22-2月 -81 1250 500 30
7566 JONES MANAGER 7839 02-4月 -81 2975 20
7654 MARTIN SALESMAN 7698 28-9月 -81 1250 1400 30
7698 BLAKE MANAGER 7839 01-5月 -81 2850 30
7782 CLARK MANAGER 7839 09-6月 -81 2450 10
7788 SCOTT ANALYST 7566 09-12月-82 3000 20
7839 KING PRESIDENT 17-11月-81 5000 10
7844 TURNER SALESMAN 7698 08-9月 -81 1500 0 30
7876 ADAMS CLERK 7788 12-1月 -83 1100 20
7900 JAMES CLERK 7698 03-12月-81 950 30
7902 FORD ANALYST 7566 03-12月-81 3000 20
7934 MILLER CLERK 7782 23-1月 -82 1300 10
已选择14行。
SQL> select * from emp2 order by 1;
ENAME JOB SAL
---------- ---------- ----------
ADAMS CLERK 1100
ADAMS CLERK 1100
JAMES CLERK 950
JAMES CLERK 950
MILLER CLERK 1300
MILLER CLERK 1300
SMITH CLERK 800
SMITH CLERK 800
已选择8行。
SQL> SELECT empno, ename, job, sal, deptno
2 FROM emp
3 WHERE (ename, job, sal) IN (SELECT ename, job, sal FROM emp2);
EMPNO ENAME JOB SAL DEPTNO
---------- ---------- ---------- ---------- ----------
7369 SMITH CLERK 800 20
7876 ADAMS CLERK 1100 20
7900 JAMES CLERK 950 30
7934 MILLER CLERK 1300 10
SQL> SELECT a.empno, a.ename, a.job, a.sal, a.deptno
2 FROM emp a
3 INNER JOIN emp2 b ON (b.ename = a.ename AND b.job = a.job AND
4 b.sal = a.sal);
EMPNO ENAME JOB SAL DEPTNO
---------- ---------- ---------- ---------- ----------
7369 SMITH CLERK 800 20
7369 SMITH CLERK 800 20
7876 ADAMS CLERK 1100 20
7876 ADAMS CLERK 1100 20
7900 JAMES CLERK 950 30
7900 JAMES CLERK 950 30
7934 MILLER CLERK 1300 10
7934 MILLER CLERK 1300 10
已选择8行。
由于EMP2表有重复数据,导致半连接的写法数据翻倍,得去除重复数据
SQL> SELECT distinct a.empno, a.ename, a.job, a.sal, a.deptno
2 FROM emp a
3 INNER JOIN emp2 b ON (b.ename = a.ename AND b.job = a.job AND
4 b.sal = a.sal);
EMPNO ENAME JOB SAL DEPTNO
---------- ---------- ---------- ---------- ----------
7900 JAMES CLERK 950 30
7876 ADAMS CLERK 1100 20
7369 SMITH CLERK 800 20
7934 MILLER CLERK 1300 10
IN 有空值的情况呢？
SQL> select * from emp2 order by 6 nulls last;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- ---------- ---------- -------------- ---------- ---------- ----------
7876 ADAMS CLERK 7788 12-1月 -83 1100 20
7521 WARD SALESMAN 7698 22-2月 -81 1250 500 30
7654 MARTIN SALESMAN 7698 28-9月 -81 1250 1400 30
7934 MILLER CLERK 7782 23-1月 -82 1300 10
7844 TURNER SALESMAN 7698 08-9月 -81 1500 0 30
7499 ALLEN SALESMAN 7698 20-2月 -81 1600 300 30
7782 CLARK MANAGER 7839 09-6月 -81 2450 10
7698 BLAKE MANAGER 7839 01-5月 -81 2850 30
7566 JONES MANAGER 7839 02-4月 -81 2975 20
7788 SCOTT ANALYST 7566 09-12月-82 3000 20
7902 FORD ANALYST 7566 03-12月-81 3000 20
7839 KING PRESIDENT 17-11月-81 5000 10
7369 SMITH CLERK 7902 17-12月-80 20
7900 JAMES CLERK 7698 03-12月-81 30
已选择14行。
SQL> select * from emp3 order by 3 nulls last;
ENAME JOB SAL
---------- ---------- ----------
ADAMS CLERK 1100
MILLER CLERK 1300
JAMES CLERK
SMITH CLERK
此时
SQL> SELECT empno, ename, job, sal, deptno
2 FROM emp2
3 WHERE (ename, job, sal) IN (SELECT ename, job, sal FROM emp3);
EMPNO ENAME JOB SAL DEPTNO
---------- ---------- ---------- ---------- ----------
7876 ADAMS CLERK 1100 20
7934 MILLER CLERK 1300 10
会丢失 SMITH和JAMES 2条记录,改写为:
SQL> SELECT empno, ename, job, sal, deptno
2 FROM emp2
3 WHERE (ename || job || sal) IN (SELECT ename || job || sal FROM emp3);
EMPNO ENAME JOB SAL DEPTNO
---------- ---------- ---------- ---------- ----------
7369 SMITH CLERK 20
7876 ADAMS CLERK 1100 20
7900 JAMES CLERK 30
7934 MILLER CLERK 1300 10