Mysql DBA 高级运维学习笔记-删除表中数据

Posted 2020-10-22

9.11 删除表中数据

1. 命令语法：delete from 表名 where 表达式

实践：

（1）删除表student中编号为3的记录

mysql> use zbf
Database changed
mysql> select * from student;
+----+-----------+-----+--------+
| id | name  | age | dept   |
+----+-----------+-----+--------+
|  1 | zbf666|  29 | linux  |
|  2 | lisi  |  28 | mysql  |
|  3 | zhangsan  |  21 | python |
|  4 | woshishei |  24 | java   |
+----+-----------+-----+--------+
4 rows in set (0.06 sec)

mysql> delete from student where id=3;
Query OK, 1 row affected (0.01 sec)

mysql> select * from student;
+----+-----------+-----+-------+
| id | name  | age | dept  |
+----+-----------+-----+-------+
|  1 | zbf666|  29 | linux |
|  2 | lisi  |  28 | mysql |
|  4 | woshishei |  24 | java  |
+----+-----------+-----+-------+
3 rows in set (0.02 sec)

（2）也可以删除name等于lisi的行

mysql> select * from student;
+----+-----------+-----+-------+
| id | name  | age | dept  |
+----+-----------+-----+-------+
|  1 | zbf666|  29 | linux |
|  2 | lisi  |  28 | mysql |
|  4 | woshishei |  24 | java  |
+----+-----------+-----+-------+
3 rows in set (0.02 sec)

mysql> delete from student where name=‘lisi‘;
Query OK, 1 row affected (0.01 sec)

mysql> select * from student;
+----+-----------+-----+-------+
| id | name  | age | dept  |
+----+-----------+-----+-------+
|  1 | zbf666|  29 | linux |
|  4 | woshishei |  24 | java  |
+----+-----------+-----+-------+
2 rows in set (0.00 sec)

（3）也可以删除id大于3的行

mysql> select * from student;
+----+-----------+-----+-------+
| id | name  | age | dept  |
+----+-----------+-----+-------+
|  1 | zbf666|  29 | linux |
|  4 | woshishei |  24 | java  |
+----+-----------+-----+-------+
2 rows in set (0.00 sec)

mysql> delete from student where id>3;
Query OK, 1 row affected (0.01 sec)

mysql> select * from student;
+----+--------+-----+-------+
| id | name   | age | dept  |
+----+--------+-----+-------+
|  1 | zbf666 |  29 | linux |
+----+--------+-----+-------+
1 row in set (0.00 sec)

提示：不加条件就是全部删除，也是非常危险的操作，这里接不演示了。delete from student 。

2.命令语法Truncate table 表名

Truncate table student; 清空表中所欲内容

mysql> truncate table student;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from student;
Empty set (0.00 sec)

Truncate from srudent和delete from student区别

a.Truncate table student;更快，清空物理文件。

b.delete from student;逻辑清除，按行删。