MySQL insert语句

 

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| course             |
| information_schema |
| monitor            |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
6 rows in set (0.03 sec)

mysql> use course;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> show tables;
+------------------+
| Tables_in_course |
+------------------+
| course           |
| dept             |
| students         |
| teacher          |
+------------------+
4 rows in set (0.01 sec)

mysql> desc dept;
+-----------+-------------+------+-----+---------+----------------+
| Field     | Type        | Null | Key | Default | Extra          |
+-----------+-------------+------+-----+---------+----------------+
| id        | int(11)     | NO   | PRI | NULL    | auto_increment |
| dept_name | varchar(64) | YES  |     | NULL    |                |
+-----------+-------------+------+-----+---------+----------------+
2 rows in set (0.01 sec)

mysql> insert into dept(dept_name,id) values('a',1);
Query OK, 1 row affected (0.04 sec)

mysql> delete from dept;
Query OK, 1 row affected (0.06 sec)

mysql> insert into dept(dept_name,id) values("a",1);
Query OK, 1 row affected (0.02 sec)

mysql> select * from dept;
+----+-----------+
| id | dept_name |
+----+-----------+
|  1 | a         |
+----+-----------+
1 row in set (0.00 sec)

mysql> create table dept_bak(id int primary key auto_increment,dept_name varchar(64));
Query OK, 0 rows affected (0.07 sec)

mysql> insert into dept_bak values(1,'a'),(2,'b');
Query OK, 2 rows affected (0.04 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from dept_bak;
+----+-----------+
| id | dept_name |
+----+-----------+
|  1 | a         |
|  2 | b         |
+----+-----------+
2 rows in set (0.00 sec)

mysql> select *  from dept;
+----+-----------+
| id | dept_name |
+----+-----------+
|  1 | a         |
+----+-----------+
1 row in set (0.00 sec)

mysql> delete from dept;
Query OK, 1 row affected (0.08 sec)

mysql> insert into dept select * from dept_bak;
Query OK, 2 rows affected (0.05 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from dept;
+----+-----------+
| id | dept_name |
+----+-----------+
|  1 | a         |
|  2 | b         |
+----+-----------+
2 rows in set (0.00 sec)

mysql> desc dept_bak;
+-----------+-------------+------+-----+---------+----------------+
| Field     | Type        | Null | Key | Default | Extra          |
+-----------+-------------+------+-----+---------+----------------+
| id        | int(11)     | NO   | PRI | NULL    | auto_increment |
| dept_name | varchar(64) | YES  |     | NULL    |                |
+-----------+-------------+------+-----+---------+----------------+
2 rows in set (0.01 sec)

mysql> alter table dept_bak add name varchar(10);
Query OK, 0 rows affected (0.13 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from dept_bak;
+----+-----------+------+
| id | dept_name | name |
+----+-----------+------+
|  1 | a         | NULL |
|  2 | b         | NULL |
+----+-----------+------+
2 rows in set (0.00 sec)

mysql> select * from dept;
+----+-----------+
| id | dept_name |
+----+-----------+
|  1 | a         |
|  2 | b         |
+----+-----------+
2 rows in set (0.00 sec)

mysql> delete from dept;
Query OK, 2 rows affected (0.09 sec)

mysql> insert into dept select id,dept_name from dept_bak;
Query OK, 2 rows affected (0.06 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> delete from dept;
Query OK, 4 rows affected (0.03 sec)

mysql> insert into dept(dept_name) select concat(id,dept_name) from dept_bak;
Query OK, 2 rows affected (0.03 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from dept;
+----+-----------+
| id | dept_name |
+----+-----------+
|  6 | 1a        |
|  7 | 2b        |
+----+-----------+
2 rows in set (0.01 sec)

• 当insert语句中使用on duplicate key update子句时，如果碰到当前插入的数据违反主键或唯一键的唯一性约束，则Insert会转变成update语句修改对应的已经存在表中的这条数据。比如如果a字段有唯一性约束且已经含有1这条记录，则以下两条语句的执行结果相同

• INSERT INTO table (a,b,c) VALUES (1,2,3)
ON DUPLICATE KEY UPDATE c=c+1;
• UPDATE table SET c=c+1 WHERE a=1;

• On duplicate key update子句后面可以跟多个修改，用逗号隔开
• 上述例子中如果b字段也有唯一性约束，则与此语句的执行结果相同，但一般应该避免出现对应多条的情况

• UPDATE table SET c=c+1 WHERE a=1 OR b=2 LIMIT 1;

 

• mysql> create table students2(sid int primary key,sname varchar(20),sex int);
• Insert into students2 values(1,’aaa’,1); ##插入成功
• Insert into students2 values(1,’bbb’,0); ##插入失败
• mysql> insert into students2 values(1,'bbb',0);
• ERROR 1062 (23000): Duplicate entry '1' for key 'PRIMARY‘
• insert into students2 values(1,‘bbb’,0) on duplicate key update sname=‘bbb’; ##执行成功
• +-----+-------+------+
• | sid | sname | sex  |
• +-----+-------+------+
• | 1   | bbb   | 1    |
• insert into students2 values(1,‘ccc’,0) on duplicate key update sname=‘ccc’,sex=0; ##执行成功

 

mysql> create table students2(sid int primary key,sname varchar(20),sex int);
Query OK, 0 rows affected (0.11 sec)

mysql> Insert into students2 values(1,'aaa',1);
Query OK, 1 row affected (0.19 sec)

mysql> desc students2
    -> ;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| sid   | int(11)     | NO   | PRI | NULL    |       |
| sname | varchar(20) | YES  |     | NULL    |       |
| sex   | int(11)     | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> Insert into students2 values(1,'bbb',0);
ERROR 1062 (23000): Duplicate entry '1' for key 'PRIMARY'
mysql> insert into students2 values(1,'bbb',0) on duplicate key update sname='bbb';
Query OK, 2 rows affected (0.05 sec)

mysql> select * from students2;
+-----+-------+------+
| sid | sname | sex  |
+-----+-------+------+
|   1 | bbb   |    1 |
+-----+-------+------+
1 row in set (0.00 sec)