Mysql数据库修改字段名和修改字段类型的实例

alter table table1 modify column column1 decimal(10,1) DEFAULT NULL COMMENT ‘注释’; — 正常，能修改字段类型、类型长度、默认值、注释

alter table table1 modify column1 decimal(10,2) DEFAULT NULL COMMENT ‘注释’;
— 正常，能修改字段类型、类型长度、默认值、注释

mysql修改字段名：
ALTER TABLE 表名 CHANGE [column] 旧字段名 新字段名 新数据类型;
alter table table1 change column1 column1 varchar(100) DEFAULT 1.2 COMMENT ‘注释’; — 正常，此时字段名称没有改变，能修改字段类型、类型长度、默认值、注释
alter table table1 change column1 column2 decimal(10,1) DEFAULT NULL COMMENT ‘注释’ — 正常，能修改字段名、字段类型、类型长度、默认值、注释
alter table table1 change column2 column1 decimal(10,1) DEFAULT NULL COMMENT ‘注释’ — 正常，能修改字段名、字段类型、类型长度、默认值、注释
alter table table1 change column1 column2; — 报错

mysql> alter table white_user change column name nick_name varchar(50) null comment ‘昵称’; — 正确
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> show tables ;
+——————-+
| Tables_in_db_test |
+——————-+
| white_user |
+——————-+
1 row in set (0.00 sec)

mysql> alter table white_user rename to white_user_new ;
Query OK, 0 rows affected (0.00 sec)

mysql> show tables ;
+——————-+
| Tables_in_db_test |
+——————-+
| white_user_new |
+——————-+
1 row in set (0.00 sec)

mysql> alter table white_user_new comment ‘新表-白名单表’ ;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> show create table white_user_new ;
CREATE TABLE `white_user_new` (
`id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT ‘ID’,
`name` varchar(50) NOT NULL COMMENT ‘姓名’,
`created_time` datetime DEFAULT NULL COMMENT ‘创建时间’,
`updated_time` datetime DEFAULT NULL COMMENT ‘更新时间’,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 COMMENT=’新表-白名单表’

mysql> alter table white_user_new add column erp varchar(50) not null comment ‘erp账号’ after name ;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
–在name字段后面添加erp字段

mysql> show create table white_user_new ;
CREATE TABLE `white_user_new` (
`id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT ‘ID’,
`name` varchar(50) NOT NULL COMMENT ‘姓名’,
`erp` varchar(50) NOT NULL COMMENT ‘erp账号’,
`created_time` datetime DEFAULT NULL COMMENT ‘创建时间’,
`updated_time` datetime DEFAULT NULL COMMENT ‘更新时间’,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 COMMENT=’新表-白名单表’

mysql> alter table white_user_new add position varchar(50) not null comment ‘岗位’ after name ;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
–在name字段后面添加position字段。

mysql> show create table white_user_new ;
CREATE TABLE `white_user_new` (
`id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT ‘ID’,
`name` varchar(50) NOT NULL COMMENT ‘姓名’,
`position` varchar(50) NOT NULL COMMENT ‘岗位’,
`erp` varchar(50) NOT NULL COMMENT ‘erp账号’,
`created_time` datetime DEFAULT NULL COMMENT ‘创建时间’,
`updated_time` datetime DEFAULT NULL COMMENT ‘更新时间’,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 COMMENT=’新表-白名单表’

mysql> alter table white_user_new add mobile varchar(50) not null comment ‘手机号码’ before position ;
–报错，在position字段前添加mobile字段，不能使用before关键字

mysql> alter table white_user_new drop column position ;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> alter table white_user_new drop erp ;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> show create table white_user_new ;
CREATE TABLE `white_user_new` (
`id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT ‘ID’,
`name` varchar(50) NOT NULL COMMENT ‘姓名’,
`created_time` datetime DEFAULT NULL COMMENT ‘创建时间’,
`updated_time` datetime DEFAULT NULL COMMENT ‘更新时间’,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 COMMENT=’新表-白名单表’