目录
一、修改列定义(modify col_name)
二、修改列类型(modify col_name)
三、修改列名称(change col_name)
三、修改表名称(rename table a to b)
用到的语句
a、修改列定义和名称:
语法一:Alter table tbl_name modify[column] col_name [first|after col_name]
讲解:更改 数据表 某某表 修改 【列】 列名称 列定义 【位置|位置】
语法二:alter table tab_name change[column] old_name new_name [first|after col_name]
讲解:更改 数据表 某某表 修改 【列】 列名称 列定义 【位置|位置】
注意:语法二的功能要比语法一大很多,因为语法二既可以更改列定义,由可以更改列名称
b、修改表名称:
语法一: alter table tbl_name rename[to|as] new_tbl_name
讲解:可以更改一张数据表名称
语法二:rename table tbl_name to new_tbl_name [,tbl_name2 TO new_tbl_namew]……
讲解:可以多表更改名称
一、修改列定义(改变age列的位置,使用modify)
先确定我们数据库存在我们操作的数据表city2mysql> show columns from city2;//查询数据表+----------+----------------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+----------+----------------------+------+-----+---------+-------+| id | smallint(5) unsigned | NO || 0 | || username | varchar(20)| NO || NULL | || pid| smallint(5) unsigned | YES || NULL | || age| tinyint(3) unsigned | NO || NULL | |+----------+----------------------+------+-----+---------+-------+
案例
//具体操作语句:更改数据表city2,修改age列 位于username之后mysql> alter table city2 modify age tinyint unsigned NOT NULL after username;Query OK, 0 rows affected (0.21 sec)//修改成功//修改前age列位于pid之下mysql> show columns from city2;+----------+----------------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+----------+----------------------+------+-----+---------+-------+| id | smallint(5) unsigned | NO || 0 | || username | varchar(20)| NO || NULL | || pid| smallint(5) unsigned | YES || NULL | || age| tinyint(3) unsigned | NO || NULL | |+----------+----------------------+------+-----+---------+-------+//修改后,age位于username之下,pid之上+----------+----------------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+----------+----------------------+------+-----+---------+-------+| id | smallint(5) unsigned | NO || 0 | || username | varchar(20)| NO || NULL | || age| tinyint(3) unsigned | NO || NULL | || pid| smallint(5) unsigned | YES || NULL | |+----------+----------------------+------+-----+---------+-------+4 rows in set (0.01 sec)
二、修改列类型(修改age列的储存类型,使用modify)
注意:由大类型改变成小类型的时候有可能造成数据的丢失
语句: alter table city2 modify age smallint unsigned NOT NULL;
解析:更改数据表city2 修改age列,类型:smallint,无符号,非空
//具体操作mysql> alter table city2 modify age smallint unsigned NOT NULL;Query OK, 0 rows affected (0.18 sec)//修改成功//查询数据表mysql> show columns from city2;//修改前,age的类型为tinyint+----------+----------------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+----------+----------------------+------+-----+---------+-------+| id | smallint(5) unsigned | NO || 0 | || username | varchar(20)| NO || NULL | || age| tinyint(3) unsigned | NO || NULL | || pid| smallint(5) unsigned | YES || NULL | |+----------+----------------------+------+-----+---------+-------+//修改后,age的类型改变为smallint+----------+----------------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+----------+----------------------+------+-----+---------+-------+| id | smallint(5) unsigned | NO || 0 | || username | varchar(20)| NO || NULL | || age| smallint(5) unsigned | NO || NULL | || pid| smallint(5) unsigned | YES || NULL | |+----------+----------------------+------+-----+---------+-------+
三、修改列名称(使用change改变列的名称和类型,使用change)
注意:change col_name 不仅仅可以修改列定义,还可以修改列的名称。
语法:alter table tab_name change[column] old_name new_name [first|after col_name]
解析:更改数据表某某,改变列 老列名 新列明 列定于【位置first|某列之后】
语法:alter table city2 change pid p_id tinyint unsigned not null解析:更改数据表city2 改变pid列 老名称:pid,新名称:p_id,类型:tinyint ,无符号,非空。mysql> alter table city2 change pid p_id tinyint unsigned not null;Query OK, 0 rows affected (0.20 sec)//修改成功过mysql> show columns from city2;//修改前,数据表的名称pid 类型为smallint+----------+----------------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+----------+----------------------+------+-----+---------+-------+| id | smallint(5) unsigned | NO || 0 | || username | varchar(20)| NO || NULL | || age| smallint(5) unsigned | NO || NULL | || pid| smallint(5) unsigned | YES || NULL | |+----------+----------------------+------+-----+---------+-------+//修改后,pid列名称改变为p_id,类型由smallint改变为tinyint+----------+----------------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+----------+----------------------+------+-----+---------+-------+| id | smallint(5) unsigned | NO || 0 | || username | varchar(20)| NO || NULL | || age| smallint(5) unsigned | NO || NULL | || p_id| tinyint(3) unsigned | NO || NULL | |+----------+----------------------+------+-----+---------+-------+4 rows in set (0.01 sec)
三、修改表名称
注意:修改数据表的名称有两种方式。一、方法一 单列改名//可以更改一张数据表
1、alter table tbl_name rename[to|as] new_tbl_name
//可以为多张数据表修改名称
2、rename table tbl_name to new_tbl_name [,tbl_name2 TO new_tbl_namew]……
语句:show tables;解析:查看数据库里有那些数据表语句:alter table city2 rename city222;解析:更改数据表名称tity2 更改为名称city222mysql> show tables;+--------------+| Tables_in_t1 |+--------------+| city || city1 || city2 || mm1|| mm2|| mm3|| sheng |+--------------+//我们修改city2的表名称为city222mysql> alter table city2 rename city222;Query OK, 0 rows affected (0.07 sec)//修改成功mysql> show tables;//修改前,数据表city2存在+--------------+| Tables_in_t1 |+--------------+| city || city1 || city2 || mm1|| mm2|| mm3|| sheng |+--------------+//修改后,city2数据表变成了city222+--------------+| Tables_in_t1 |+--------------+| city || city1 || city222|| mm1|| mm2|| mm3|| sheng |+--------------+
方法二,多列改名
mysql> rename table city to city_1,city222 to city2;Query OK, 0 rows affected (0.17 sec)//修改成功mysql> show tables;//修改前,city和city111数据表存在+--------------+| Tables_in_t1 |+--------------+| city || city1 || city222|| mm1|| mm2|| mm3|| sheng |+--------------+//city和city111数据表的名称 改变为了 city_1 和city2。+--------------+| Tables_in_t1 |+--------------+| city1 || city2 || city_1 || mm1|| mm2|| mm3|| sheng |+--------------+
注意:我们尽量不要去修改表的名称和列的名称。因为我们在代码中或者某项操作中引用了此数据表或者表的列,我们更改后可能会导致某些试图和存储过程无法正常工作。所以尽量不要去修改数据表名和列名
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