MySQL学习之SQL基础（一）DML
2024-09-07 07:56:23
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
- 更新一张表
UPDATE emp set sal=11000 where ename='lisa';
- 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
- 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)
- 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)
- 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)
- 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)
- 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;
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