1、一个表要删除全部数据如何实现：①delete，②truncate
EG：删除a表中的所有数据：
CREATE TABLE `b` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) NOT NULL DEFAULT '',
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=16711412 DEFAULT CHARSET=utf8;
快速导入数据：
insert into a(name) values('qcj');
insert into a(name) values('qcj_a');
insert into a(name) values('qcj_b');
insert into a(name) select name from a;
mysql> insert into a(name) select name from a;
Query OK, 25165824 rows affected (32 min 53.16 sec)
Records: 25165824 Duplicates: 0 Warnings:
将a表重新复制一份b
测试：
复制表a，delete和truncate分别删除表测试：
mysql> truncate table b;
Query OK, 0 rows affected (5.79 sec)
mysql> delete from a;
Query OK, 50331648 rows affected (32 min 29.32 sec)
show tables status like 'table_name'
mysql> show table status like 'a'G;
*************************** 1. row ***************************
Name: a
Engine: InnoDB
Version: 10
Row_format: Compact
Rows: 0
Avg_row_length: 0
Data_length: 1509949440
Max_data_length: 0
Index_length: 0
Data_free: 335544320
Auto_increment: 50920682
Create_time: 2016-03-23 14:44:34
Update_time: NULL
Check_time: NULL
Collation: utf8_general_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)
ERROR:
No query specified
mysql> show table status like 'b'G;
*************************** 1. row ***************************
Name: b
Engine: InnoDB
Version: 10
Row_format: Compact
Rows: 0
Avg_row_length: 0
Data_length: 16384
Max_data_length: 0
Index_length: 0
Data_free: 0
Auto_increment: 1
Create_time: 2016-03-23 15:22:55
Update_time: NULL
Check_time: NULL
Collation: utf8_general_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)
ERROR:
No query specified
区别：
1.delete 删除表后，会存在碎片 并且 删除后，不会自增ID号的派发
2.truncate只能一次清空，不能按条件删除。但是delete可以按条件清除部分记录。
3.truncate清空数据表性能（速度）比delete快。
4.truncate不会记录到系统日志，不会触发delete触发器