Truncate table语句用来删除/截断表里的所有数据

和delete删除所有表数据在逻辑上含义相同，但性能更快

类似执行了drop table和create table两个语句

mysql> select * from students_bak;

+-----+----------+--------+---------+

| sid | sname | gender | dept_id |

+-----+----------+--------+---------+

| 101 | zhangsan | male | 10 |

| 1 | aa | 1 | 1 |

+-----+----------+--------+---------+

2 rows in set (0.00 sec)

mysql> truncate table students_bak;

Query OK, 0 rows affected (0.16 sec)

mysql> select * from students_bak;

Empty set (0.00 sec)

mysql> set autocommit=off;

Query OK, 0 rows affected (0.01 sec)

mysql> select * from students3;

+-----+-------+--------+---------+--------+

| sid | sname | gender | dept_id | sname2 |

+-----+-------+--------+---------+--------+

| 100 | NULL | 1 | 1 | NULL |

+-----+-------+--------+---------+--------+

1 row in set (0.01 sec)

mysql> truncate table students3;

Query OK, 0 rows affected (0.06 sec)

mysql> rollback;

Query OK, 0 rows affected (0.00 sec)

mysql> select * from students3;

Empty set (0.00 sec)

mysql> delete from students;

Query OK, 5 rows affected (0.00 sec)

mysql> select * from students;

Empty set (0.00 sec)

mysql> rollback;

Query OK, 0 rows affected (0.07 sec)

mysql> select * from students;

+-----+-------+--------+---------+

| sid | sname | gender | dept_id |

+-----+-------+--------+---------+

| 1 | aa | 3 | 1 |

| 4 | cc | 3 | 1 |

| 5 | dd | 1 | 2 |

| 6 | aac | 1 | 1 |

| 10 | a | 1 | 1 |

+-----+-------+--------+---------+

5 rows in set (0.00 sec)

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时间： 2021-03-16