MySQL学习之SQL基础（一）DML

DML（data Manipulation language）

INSERT DELETE UPDATE SELECT

INSERT

mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field    | Type          | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename    | varchar(25)   | YES  |     | NULL    |       |
| hiredate | date          | YES  |     | NULL    |       |
| sal      | decimal(10,2) | YES  |     | NULL    |       |
| deptno   | int(2)        | YES  |     | NULL    |       |
+----------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql>

INSERT INTO emp (ename,hiredate,sal ,deptno) VALUES ('zzx','2000-01-01',100,1);

INSERT INTO emp VALUES('lisa','2003-02-01',400,2);

一次性插入多条记录

INSERT INTO emp VALUES('jack','2018-09-21',12000,1),
('tony','2018-09-21',13000,4)
;

UPDATE

1. 更新一张表

UPDATE emp set sal=11000 where ename='lisa';

2. 多表更新

首先创建一张表部门表

CREATE TABLE dept(
deptno int (3) ,
deptname varchar(25)
);

mysql> desc dept;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| deptno   | int(3)      | YES  |     | NULL    |       |
| deptname | varchar(25) | YES  |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)

INSERT dept VALUES(1,'tech');
INSERT INTO dept VALUES (2,'sale'),(3,'fin');

mysql> select * from emp;
+-------+------------+----------+--------+
| ename | hiredate   | sal      | deptno |
+-------+------------+----------+--------+
| zzx   | 2000-01-01 |   100.00 |      1 |
| lisa  | 2003-02-01 | 11000.00 |      2 |
| jack  | 2018-09-21 | 12000.00 |      1 |
| tony  | 2018-09-21 | 13000.00 |      4 |
+-------+------------+----------+--------+
4 rows in set (0.00 sec)

多表更新

UPDATE emp a ,dept b SET a.sal =a.sal * b.deptno WHERE a.deptno=b.deptno;
mysql> SELECT * FROM emp;
+-------+------------+----------+--------+
| ename | hiredate   | sal      | deptno |
+-------+------------+----------+--------+
| zzx   | 2000-01-01 |   100.00 |      1 |
| lisa  | 2003-02-01 | 22000.00 |      2 |
| jack  | 2018-09-21 | 12000.00 |      1 |
| tony  | 2018-09-21 | 13000.00 |      4 |
+-------+------------+----------+--------+
4 rows in set (0.00 sec)

查询表

1. 查询去重，DISTINCT只能显示一列

mysql> SELECT  DISTINCT deptno FROM emp;
+--------+
| deptno |
+--------+
|      1 |
|      2 |
|      4 |
+--------+
3 rows in set (0.00 sec)

2. 条件查询

mysql> SELECT * FROM emp;
+-------+------------+----------+--------+
| ename | hiredate   | sal      | deptno |
+-------+------------+----------+--------+
| zzx   | 2000-01-01 |   100.00 |      1 |
| lisa  | 2003-02-01 | 22000.00 |      2 |
| jack  | 2018-09-21 | 12000.00 |      1 |
| tony  | 2018-09-21 | 13000.00 |      4 |
+-------+------------+----------+--------+


mysql> SELECT  ename,sal FROM emp WHERE deptno<=1 AND sal > 5000;
+-------+----------+
| ename | sal      |
+-------+----------+
| jack  | 12000.00 |
+-------+----------+
1 row in set (0.00 sec)

3、排序查询
查询emp排序后第二条之后的三条记录

mysql> SELECT * FROM emp;
+-------+------------+----------+--------+
| ename | hiredate   | sal      | deptno |
+-------+------------+----------+--------+
| zzx   | 2000-01-01 |   100.00 |      1 |
| lisa  | 2003-02-01 | 22000.00 |      2 |
| jack  | 2018-09-21 | 12000.00 |      1 |
| tony  | 2018-09-21 | 13000.00 |      4 |
+-------+------------+----------+--------+
4 rows in set (0.00 sec)

mysql> SELECT * FROM emp order by sal LIMIT 1,3;
+-------+------------+----------+--------+
| ename | hiredate   | sal      | deptno |
+-------+------------+----------+--------+
| jack  | 2018-09-21 | 12000.00 |      1 |
| tony  | 2018-09-21 | 13000.00 |      4 |
| lisa  | 2003-02-01 | 22000.00 |      2 |
+-------+------------+----------+--------+
3 rows in set (0.00 sec)

4. 聚合
   统计emp总人数

mysql> SELECT COUNT(1) FROM emp;
+----------+
| COUNT(1) |
+----------+
|        4 |
+----------+
1 row in set (0.00 sec)

统计各个部门的总人数

mysql> SELECT deptno  FROM emp GROUP BY deptno;
+--------+
| deptno |
+--------+
|      1 |
|      2 |
|      4 |
+--------+
3 rows in set (0.00 sec)
mysql> SELECT deptno,COUNT(1) FROM emp GROUP BY deptno;
+--------+----------+
| deptno | COUNT(1) |
+--------+----------+
|      1 |        2 |
|      2 |        1 |
|      4 |        1 |
+--------+----------+
3 rows in set (0.00 sec)

统计各个部门的总人数也要统计总人数
with rollup进行再次汇总

 SELECT deptno,COUNT(1) FROM emp GROUP BY deptno WITH rollup;

统计各个部门的总人数大于等于2
使用having进行条件过滤

mysql> SELECT deptno,COUNT(1) FROM emp GROUP BY deptno  HAVING COUNT(1)>=2;
+--------+----------+
| deptno | COUNT(1) |
+--------+----------+
|      1 |        2 |
+--------+----------+
1 row in set (0.00 sec)

5. 子查询

查询emp表中部门编号在dept表的员工

| ename | hiredate   | sal      | deptno |
+-------+------------+----------+--------+
| zzx   | 2000-01-01 |   100.00 |      1 |
| lisa  | 2003-02-01 | 22000.00 |      2 |
| jack  | 2018-09-21 | 12000.00 |      1 |
| tony  | 2018-09-21 | 13000.00 |      4 |
+-------+------------+----------+--------+
4 rows in set (0.01 sec)

mysql> SELECT * FROM emp order by sal LIMIT 1,3;^C
mysql> SELECT * FROM dept;
+--------+----------+
| deptno | deptname |
+--------+----------+
|      1 | tech     |
|      2 | sale     |
|      3 | fin      |
+--------+----------+
3 rows in set (0.00 sec)
mysql> SELECT ename ,sal from emp where deptno in (select deptno from dept);
+-------+----------+
| ename | sal      |
+-------+----------+
| zzx   |   100.00 |
| lisa  | 22000.00 |
| jack  | 12000.00 |
+-------+----------+
3 rows in set (0.00 sec)

6. 联合
   将查询结果合并显示

• 查询所有的的deptno，去重

SELECT deptno FROM emp UNION
 SELECT deptno FROM dept;

• 查询所有的的deptno，不去重

SELECT deptno FROM emp UNION all
 SELECT deptno FROM dept;