Oracle入门学习（7）

WHERE子句(2)

逻辑运算符的使用

NOT, AND, OR 

1.IS NULL

SELECT ID, NAME, SALES_REP_ID

FROM S_CUSTOMER

WHERE SALES_REP_ID IS NULL;

 

 

如果用“=”号去匹配是否为空是错误的

SELECT ID, NAME, SALES_REP_ID

FROM S_CUSTOMER

WHERE SALES_REP_ID = NULL;

 

 

2.逻辑运算符的使用

NOT, AND, OR

 

SELECT LAST_NAME, SALARY, TITLE

FROM S_EMP

WHERE DEPT_ID = 41

AND TITLE = 'Stock Clerk';

 

 

 

SELECT LAST_NAME, SALARY, TITLE

FROM S_EMP

WHERE DEPT_ID = 41

OR TITLE = 'Stock Clerk';

 

 

 

逻辑运算符的优先级：

NOT > AND > OR

 

SELECT LAST_NAME, SALARY, DEPT_ID

FROM S_EMP

WHERE SALARY >= 1000

AND DEPT_ID = 44

OR DEPT_ID = 42;

其中：SALARY >= 1000 AND DEPT_ID = 44

与DEPT_ID = 42; 是或的关系

 

SELECT LAST_NAME, SALARY, DEPT_ID

FROM S_EMP

WHERE SALARY >= 1000

AND (DEPT_ID = 44

OR DEPT_ID = 42);