SQL查询系列之八：SQL子查询

时间 2019-11-12

标签 sql 查询系列之八栏目 SQL 繁體版

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当一个查询是另外一个查询的条件时，称之为子查询。子查询可使用几个简单命令构造功能强大的复合命令。code

子查询最经常使用于WHERE子句中。还用在SELECT,FROM子句中，下面分别举例说明。get

1. 子查询用WHERE子句。table

示例:显示emp表中职位为CLERK和SALESMAN的员工信息date

SQL> SELECT * FROM emp WHERE job in('CLERK','SALESMAN');select

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNOim

----- ---------- --------- ----- ----------- --------- --------- ------查询

7369 SMITH CLERK 7902 1980/12/17 800.00 20img

7499 ALLEN SALESMAN 7698 1981/2/20 1600.00 300.00 30tab

7521 WARD SALESMAN 7698 1981/2/22 1250.00 500.00 30co

7654 MARTIN SALESMAN 7698 1981/9/28 1250.00 1400.00 30

7844 TURNER SALESMAN 7698 1981/9/8 1500.00 0.00 30

7876 ADAMS CLERK 7788 1987/5/23 1100.00 20

7900 JAMES CLERK 7698 1981/12/3 950.00 30

7934 MILLER CLERK 7782 1982/1/23 1300.00 10

8 rows selected

2. 子查询用from子句。

示例:显示emp表中5-10条记录。

SQL> SELECT empno,ename,job,hiredate,sal,comm,deptno

2 FROM (SELECT ROWNUM r,emp.* FROM emp ) T

3 WHERE T.r>=5 AND T.r<10;

EMPNO ENAME JOB HIREDATE SAL COMM DEPTNO

----- ---------- --------- ----------- --------- --------- ------

7654 MARTIN SALESMAN 1981/9/28 1250.00 1400.00 30

7698 BLAKE MANAGER 1981/5/1 2850.00 30

7782 CLARK MANAGER 1981/6/9 2450.00 10

7788 SCOTT ANALYST 1987/4/19 3000.00 20

7839 KING PRESIDENT 1981/11/17 5000.00 10

5 rows selected

3.子查询用select子句

示例: 显示emp表中所员工信息及所在部门名称。

SQL> SELECT e.*,

2 (SELECT dname FROM dept WHERE deptno=e.deptno) as dname

3 FROM EMP e;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO dname

----- ---------- --------- ----- ----------- --------- --------- ------ -----

7369 SMITH CLERK 7902 1980/12/17 800.00 20 RESEARCH

7499 ALLEN SALESMAN 7698 1981/2/20 1600.00 300.00 30 SALES

7521 WARD SALESMAN 7698 1981/2/22 1250.00 500.00 30 SALES

7566 JONES MANAGER 7839 1981/4/2 2975.00 20 RESEARCH

7654 MARTIN SALESMAN 7698 1981/9/28 1250.00 1400.00 30 SALES

7698 BLAKE MANAGER 7839 1981/5/1 2850.00 30 SALES

……

14 rows selected