select a,b,c???????????????????? ---OK，只能存放單行子查詢，不能使多行子查詢

from tab1 ?????????????????---OK 可以有子查詢

where col in(em1,em2)?????? ---可以有子查詢

??????? col between a1 and a2

??????? col > 222

??????? col > ()

group by …???????????????? ---不可以有子查詢

having ….????????????????? ---可以有子查詢

order by …???????????????? ---不可以有子查詢

1.單行操作符對應單行子查詢，多行操作符對應多行子查詢。

2.按照子查詢返回的條目數，分為：單行子查詢和多行子查詢

3.單行子查詢只能使用單行比較操作符（=? >? ?>=? <? <=? <>）

4.多行子查詢只能使用多行比較操作符（int any all）

Eg:查詢員工信息和141號工種一樣的，薪水比143號員工工資高的員工

SQL> conn hr/123456

已連接。

SQL> select last_name,job_id,salary

? 2? FROM employees

? 3? WHERE job_id =

? 4??????????????? (SELECT job_id

? 5???????????????? FROM employees

? 6???????????????? WHERE employee_id = 141);

???????????????

Eg:查詢工資最低的員工信息

select last_name,job_id,salary

FROM employees

WHERE salary =

????????????? (SELECT MIN(salary)

?????????????? FROM employees);

Eg:求各個部門編號和部門的最低工資（這個最低工資要比50號部門的最低工資要高）

思路分析：看子查詢 看group by 和 having條件檢索 看檢索對象

//子查詢：求50號部門的最低工資

à檢索 各部門的最低工資? 比50號部門的最低工資 大的部門號和部門最小工資

SELECT department_id,MIN(salary)

FROM employees

GROUP By department_id

HAVING MIN(salary) >

?????????????????? (SELECT MIN(salary)

??????????????????? FROM employees

??????????????????? WHERE department_id = 50);

方法1：子查詢

SELECT *

FROM emp

WHERE DEPTNO = (SELECT deptno

??????????????? FROM dept

??????????????? WHERE dname = 'SALES');

方法2：多表查詢

SELECT e.*

FROM emp e,dept d

WHERE e.deptno = d.deptno and d.dname = 'SALES';

注意：第二種（多表查詢的執行速度比子查詢的執行速度快，因為多表查詢是一次將數據讀到內存中進行讀取，消耗內存而加快速度）

????? 第一種（子查詢要進行兩次連接數據庫的操作，連接數據庫的操作是一個耗時操作，減低了速度）。

錯誤案例：

select ename,empno,(select deptno from emp) AA from emp;

正確案例：

select ename,empno,(select deptno from emp where EMPNO = 7369) AA from emp;

select *

from (select ename,sal

???? from emp);

查詢部門名稱是*(不是)SALES 和 ACCOUNTING 的員工信息? 2種方法

select *

from emp

where deptno in

????????????? (select deptno

?????????????? from dept

?????????????? where dname = 'SALES' or dname = 'ACCOUNTING');

操作符

含義

IN

等于列表中的任何一個

ANY

和子查詢返回的任意一個值比較

ALL

和子查詢返回的所有值比較

SELECT employee_id,last_name,job_id,salary

?FROM employees

?WHERE salary < ANY

????????????????? (SELECT salary

?????????????????? FROM employees

?????????????????? WHERE job_id = 'IT_PROG')

?AND job_id <> 'IT_PROC';

SELECT employee_id,last_name,job_id,salary

FROM employees

WHERE salary < ALL

???????????????? (SELECT salary

????????????????? FROM employees

????????????????? WHERE job_id = 'IT_PROG')

AND job_id <> 'IT_PROC'

Eg: 比30號部門 任意一個員工薪高的員工信息? 大于集合中的最小值 any

select *

from emp

where sal > all(select sal

??????????????? from emp

??????????????? where deptno = 30);

等價于：

select *

from emp

where sal > (select max(sal)

??????????? from emp

??????????? where deptno = 30);

查詢是經理的員工信息

分析：

SELECT *

FROM emp

WHERE empno in(經理的集合);

實際：

select *

from emp

where empno in

???????????? (

????????????? select mgr from emp

???????????? );

select *

from emp

where empno not in

(

select mgr

from emp

where mgr is not null

);