MySQL如何增加表和给表字段赋值

本页介绍MySQL如何进行增加表和给表字段赋值的操作。

MySQL增加表和给表字段赋值

MySQL数据库对增加表和给表字段赋值的操作提供了以下几种方式：

#增加表和表结构
CREATE TABLE tianyiyun (
uid MEDIUMINT NOT NULL AUTO_INCREMENT,
user CHAR(10) NOT NULL,
PRIMARY KEY (uid)
);

1.不对新增字段赋值，数据库会自动赋值到字段中。

mysql> INSERT INTO tianyiyun (user) VALUES ('a'),('b'),('c'),('d'),('e'),('f');
Query OK, 6 rows affected (0.01 sec)
Records: 6  Duplicates: 0  Warnings: 0
mysql> select * from tianyiyun;
+-----+------+
| uid | user |
+-----+------+
|   1 | a    |
|   2 | b    |
|   3 | c    |
|   4 | d    |
|   5 | e    |
|   6 | f    |
+-----+------+
6 rows in set (0.00 sec)

mysql> show create table tianyiyun;
+-----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table     | Create Table                                                                                                                                                                                                                |
+-----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tianyiyun | CREATE TABLE `tianyiyun` (
  `uid` mediumint(9) NOT NULL AUTO_INCREMENT,
  `user` char(10) COLLATE utf8mb4_bin NOT NULL,
  PRIMARY KEY (`uid`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>

2.新增字段赋值0或者null，数据库会将新增的值填写到字段中。

mysql> INSERT INTO tianyiyun (uid,user) VALUES(0,'g');
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO tianyiyun (uid,user) VALUES(NULL,'h');
Query OK, 1 row affected (0.00 sec)
mysql> select * from tianyiyun;
+-----+------+
| uid | user |
+-----+------+
|   1 | a    |
|   2 | b    |
|   3 | c    |
|   4 | d    |
|   5 | e    |
|   6 | f    |
|   7 | g    |
|   8 | h    |
+-----+------+
8 rows in set (0.00 sec)

mysql> show create table tianyiyun;
+-----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table     | Create Table                                                                                                                                                                                                                |
+-----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tianyiyun | CREATE TABLE `tianyiyun` (
  `uid` mediumint(9) NOT NULL AUTO_INCREMENT,
  `user` char(10) COLLATE utf8mb4_bin NOT NULL,
  PRIMARY KEY (`uid`)
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

3.使用大于AUTO_INCREMENT的值，数据库会将AUTO_INCREMEN的值增加，该值也会新增到字段里面。

mysql> INSERT INTO tianyiyun (uid,user) VALUES(99,'i');
Query OK, 1 row affected (0.00 sec)
mysql> select * from tianyiyun;
+-----+------+
| uid | user |
+-----+------+
|   1 | a    |
|   2 | b    |
|   3 | c    |
|   4 | d    |
|   5 | e    |
|   6 | f    |
|   7 | g    |
|   8 | h    |
|  99 | i    |
+-----+------+
9 rows in set (0.00 sec)
mysql> show create table tianyiyun;
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table     | Create Table                                                                                                                                                                                                                  |
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tianyiyun | CREATE TABLE `tianyiyun` (
  `uid` mediumint(9) NOT NULL AUTO_INCREMENT,
  `user` char(10) COLLATE utf8mb4_bin NOT NULL,
  PRIMARY KEY (`uid`)
) ENGINE=InnoDB AUTO_INCREMENT=100 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

4.使用小于AUTO_INCREMENT的值，不会影响到数据插入。

mysql> INSERT INTO tianyiyun (uid,user) VALUES(30,'j');
Query OK, 1 row affected (0.00 sec)
mysql> select * from tianyiyun;
+-----+------+
| uid | user |
+-----+------+
|   1 | a    |
|   2 | b    |
|   3 | c    |
|   4 | d    |
|   5 | e    |
|   6 | f    |
|   7 | g    |
|   8 | h    |
|  30 | j    |
|  99 | i    |
+-----+------+
10 rows in set (0.00 sec)
mysql> show create table tianyiyun;
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table     | Create Table                                                                                                                                                                                                                  |
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tianyiyun | CREATE TABLE `tianyiyun` (
  `uid` mediumint(9) NOT NULL AUTO_INCREMENT,
  `user` char(10) COLLATE utf8mb4_bin NOT NULL,
  PRIMARY KEY (`uid`)
) ENGINE=InnoDB AUTO_INCREMENT=100 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

5.使用负值，数据也能正常插入。

mysql> INSERT INTO tianyiyun (uid,user) VALUES(-30,'k');
Query OK, 1 row affected (0.00 sec)
mysql> select * from tianyiyun;
+-----+------+
| uid | user |
+-----+------+
| -30 | k    |
|   1 | a    |
|   2 | b    |
|   3 | c    |
|   4 | d    |
|   5 | e    |
|   6 | f    |
|   7 | g    |
|   8 | h    |
|  30 | j    |
|  99 | i    |
+-----+------+
11 rows in set (0.00 sec)
mysql> show create table tianyiyun;
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table     | Create Table                                                                                                                                                                                                                  |
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tianyiyun | CREATE TABLE `tianyiyun` (
  `uid` mediumint(9) NOT NULL AUTO_INCREMENT,
  `user` char(10) COLLATE utf8mb4_bin NOT NULL,
  PRIMARY KEY (`uid`)
) ENGINE=InnoDB AUTO_INCREMENT=100 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)