1.准备
CREATE TABLE emp
(
empno INT PRIMARY KEY,
ename VARCHAR(10),
sal INT,
deptno INT
);
INSERT INTO emp VALUES (1,'smith',300,10);
INSERT INTO emp VALUES (2,'allen',NULL,10);
INSERT INTO emp VALUES (3,'ward',NULL,20);
INSERT INTO emp VALUES (4,'jones',NULL,10);
INSERT INTO emp VALUES (5,'martin',NULL,30);
INSERT INTO emp VALUES (6,'blake',200,20);
INSERT INTO emp VALUES (7,'clark',0,30);
2.使用
去重
SELECT DISTINCT deptno FROM emp;
或者组合使用(过略掉两个字段都重复的记录):
SELECT DISTINCT sal,deptno FROM emp;