MySQL复制表-INSERT INTO SELECT

基础table为：

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|  3 | haofugui | 10000 |
|  4 | guoming  |  3500 |
|  5 | haotian  |  2900 |
+----+----------+-------+
3 rows in set (0.00 sec)

mysql> describe staff;
+-------+----------+------+-----+---------+----------------+
| Field | Type     | Null | Key | Default | Extra          |
+-------+----------+------+-----+---------+----------------+
| id    | int(11)  | NO   | PRI | NULL    | auto_increment |
| name  | char(20) | YES  |     | NULL    |                |
| slary | int(11)  | YES  |     | NULL    |                |
+-------+----------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

INSERT INTO SELECT 语句从一个表复制数据，然后把数据插入到一个已存在的表（目标表）中，目标表中任何已存在的行都不会受影响。

语句1：Insert into Table2(field1,field2,…) select value1,value2,… from Table1 where condition;

语句2：Insert into Table2 select * from Table1;

说明：1）目标表Table2必须存在，MySQL不会自动创建；

             2）语句1一般用于两个表结构一致的情况，而语句2用于表结构不一致的情况；

             3）语句1中涉及的field1，field2也必须存在；

             4）若Table2有主键且不具备自动增长，则 field1， field2…中必须包括主键。

示例：

mysql> create table staff_bak_1 like staff;
Query OK, 0 rows affected (0.05 sec)

mysql> describe staff_bak_1;  //创建了一个与staff数据结构一致的空数据库，包括主键和自动增长等
+-------+----------+------+-----+---------+----------------+
| Field | Type     | Null | Key | Default | Extra          |
+-------+----------+------+-----+---------+----------------+
| id    | int(11)  | NO   | PRI | NULL    | auto_increment |
| name  | char(20) | YES  |     | NULL    |                |
| slary | int(11)  | YES  |     | NULL    |                |
+-------+----------+------+-----+---------+----------------+
3 rows in set (0.01 sec)

mysql> select * from staff_bak_1;
Empty set (0.00 sec)

mysql> insert into staff_bak_1 select * from staff;//将staff内的数据全部复制到刚才创建的空数据库
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from staff_bak_1;  //结果
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|  3 | haofugui | 10000 |
|  4 | guoming  |  3500 |
|  5 | haotian  |  2900 |
+----+----------+-------+
3 rows in set (0.00 sec)

mysql> create table staff_bak_2            //创建一个空数据库
    -> (id int auto_increment primary key,
    -> name char(20));
Query OK, 0 rows affected (0.05 sec)

mysql> describe staff_bak_2;
+-------+----------+------+-----+---------+----------------+
| Field | Type     | Null | Key | Default | Extra          |
+-------+----------+------+-----+---------+----------------+
| id    | int(11)  | NO   | PRI | NULL    | auto_increment |
| name  | char(20) | YES  |     | NULL    |                |
+-------+----------+------+-----+---------+----------------+
2 rows in set (0.01 sec)

mysql> insert into staff_bak_2(name) select name from staff where id!=5; //带where子句，将指定的记录复制到新表中。
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from staff_bak_2; //结果
+----+----------+
| id | name     |
+----+----------+
|  1 | haofugui |
|  2 | guoming  |
+----+----------+
2 rows in set (0.00 sec)