MySQL之 ALTER vs CHANGE vs MODIFY COLUMN

1.ALTER COLUMN

用于设置或者移除某一列的默认（缺省）值，

1.1用法

　　

ALTER TABLE MyTable ALTER COLUMN foo SET DEFAULT 'bar';
ALTER TABLE MyTable ALTER COLUMN foo DROP DEFAULT;

1.2 举例

mysql> desc pre_common_block;
+----------------+-----------------------+------+-----+---------+----------------+
| Field          | Type                  | Null | Key | Default | Extra          |
+----------------+-----------------------+------+-----+---------+----------------+
| bid            | mediumint(8) unsigned | NO   | PRI | NULL    | auto_increment |
| blockclass     | varchar(255)          | NO   |     | 0       |                |
| blocktype      | tinyint(1)            | NO   |     | 0       |                |
| name           | varchar(255)          | NO   |     |         |                |
| title          | text                  | NO   |     | NULL    |                |
| classname      | varchar(255)          | NO   |     |         |                |
| summary        | text                  | NO   |     | NULL    |                |
| uid            | mediumint(8) unsigned | NO   |     | 0       |                |
| username       | varchar(255)          | NO   |     |         |                |
| styleid        | smallint(6) unsigned  | NO   |     | 0       |                |
| blockstyle     | text                  | NO   |     | NULL    |                |
| picwidth       | smallint(6) unsigned  | NO   |     | 0       |                |
| picheight      | smallint(6) unsigned  | NO   |     | 0       |                |
| target         | varchar(255)          | NO   |     |         |                |
| dateformat     | varchar(255)          | NO   |     |         |                |
| dateuformat    | tinyint(1)            | NO   |     | 0       |                |
| script         | varchar(255)          | NO   |     |         |                |
| param          | text                  | NO   |     | NULL    |                |
| shownum        | smallint(6) unsigned  | NO   |     | 0       |                |
| cachetime      | int(10)               | NO   |     | 0       |                |
| cachetimerange | char(5)               | NO   |     |         |                |
| punctualupdate | tinyint(1)            | NO   |     | 0       |                |
| hidedisplay    | tinyint(1)            | NO   |     | 0       |                |
| dateline       | int(10) unsigned      | NO   |     | 0       |                |
| notinherited   | tinyint(1)            | NO   |     | 0       |                |
| isblank        | tinyint(1)            | NO   |     | 0       |                |
+----------------+-----------------------+------+-----+---------+----------------+
26 rows in set (0.14 sec)

mysql> ALTER TABLE pre_common_block  ALTER COLUMN  blocktype set  DEFAULT 5;
Query OK, 0 rows affected (0.32 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc pre_common_block;
+----------------+-----------------------+------+-----+---------+----------------+
| Field          | Type                  | Null | Key | Default | Extra          |
+----------------+-----------------------+------+-----+---------+----------------+
| bid            | mediumint(8) unsigned | NO   | PRI | NULL    | auto_increment |
| blockclass     | varchar(255)          | NO   |     | 0       |                |
| blocktype      | tinyint(1)            | NO   |     | 5       |                |
| name           | varchar(255)          | NO   |     |         |                |
| title          | text                  | NO   |     | NULL    |                |
| classname      | varchar(255)          | NO   |     |         |                |
| summary        | text                  | NO   |     | NULL    |                |
| uid            | mediumint(8) unsigned | NO   |     | 0       |                |
| username       | varchar(255)          | NO   |     |         |                |
| styleid        | smallint(6) unsigned  | NO   |     | 0       |                |
| blockstyle     | text                  | NO   |     | NULL    |                |
| picwidth       | smallint(6) unsigned  | NO   |     | 0       |                |
| picheight      | smallint(6) unsigned  | NO   |     | 0       |                |
| target         | varchar(255)          | NO   |     |         |                |
| dateformat     | varchar(255)          | NO   |     |         |                |
| dateuformat    | tinyint(1)            | NO   |     | 0       |                |
| script         | varchar(255)          | NO   |     |         |                |
| param          | text                  | NO   |     | NULL    |                |
| shownum        | smallint(6) unsigned  | NO   |     | 0       |                |
| cachetime      | int(10)               | NO   |     | 0       |                |
| cachetimerange | char(5)               | NO   |     |         |                |
| punctualupdate | tinyint(1)            | NO   |     | 0       |                |
| hidedisplay    | tinyint(1)            | NO   |     | 0       |                |
| dateline       | int(10) unsigned      | NO   |     | 0       |                |
| notinherited   | tinyint(1)            | NO   |     | 0       |                |
| isblank        | tinyint(1)            | NO   |     | 0       |                |
+----------------+-----------------------+------+-----+---------+----------------+
26 rows in set (0.02 sec)

　

2.ALTER COLUMN

用于某一数据列的重命名、修改数据类型或者删除。

2.1用法

ALTER TABLE MyTable CHANGE COLUMN foo bar VARCHAR(32) NOT NULL FIRST;
ALTER TABLE MyTable CHANGE COLUMN foo bar VARCHAR(32) NOT NULL AFTER baz;

　　

2.2 举例

mysql> desc pre_common_block;
+----------------+-----------------------+------+-----+---------+----------------+
| Field          | Type                  | Null | Key | Default | Extra          |
+----------------+-----------------------+------+-----+---------+----------------+
| bid            | mediumint(8) unsigned | NO   | PRI | NULL    | auto_increment |
| blockclass     | varchar(255)          | NO   |     | 0       |                |
| blocktype      | tinyint(1)            | NO   |     | 5       |                |
| name           | varchar(255)          | NO   |     |         |                |
| title          | text                  | NO   |     | NULL    |                |
| classname      | varchar(255)          | NO   |     |         |                |
| summary        | text                  | NO   |     | NULL    |                |
| uid            | mediumint(8) unsigned | NO   |     | 0       |                |
| username       | varchar(255)          | NO   |     |         |                |
| styleid        | smallint(6) unsigned  | NO   |     | 0       |                |
| blockstyle     | text                  | NO   |     | NULL    |                |
| picwidth       | smallint(6) unsigned  | NO   |     | 0       |                |
| picheight      | smallint(6) unsigned  | NO   |     | 0       |                |
| target         | varchar(255)          | NO   |     |         |                |
| dateformat     | varchar(255)          | NO   |     |         |                |
| dateuformat    | tinyint(1)            | NO   |     | 0       |                |
| script         | varchar(255)          | NO   |     |         |                |
| param          | text                  | NO   |     | NULL    |                |
| shownum        | smallint(6) unsigned  | NO   |     | 0       |                |
| cachetime      | int(10)               | NO   |     | 0       |                |
| cachetimerange | char(5)               | NO   |     |         |                |
| punctualupdate | tinyint(1)            | NO   |     | 0       |                |
| hidedisplay    | tinyint(1)            | NO   |     | 0       |                |
| dateline       | int(10) unsigned      | NO   |     | 0       |                |
| notinherited   | tinyint(1)            | NO   |     | 0       |                |
| isblank        | tinyint(1)            | NO   |     | 0       |                |
+----------------+-----------------------+------+-----+---------+----------------+
26 rows in set (0.02 sec)

mysql> ALTER TABLE pre_common_block CHANGE COLUMN  blocktype  changetype tinyint(1)  NOT NULL
Query OK, 2 rows affected (0.77 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> desc pre_common_block;
+----------------+-----------------------+------+-----+---------+----------------+
| Field          | Type                  | Null | Key | Default | Extra          |
+----------------+-----------------------+------+-----+---------+----------------+
| changetype     | tinyint(1)            | NO   |     | NULL    |                |
| bid            | mediumint(8) unsigned | NO   | PRI | NULL    | auto_increment |
| blockclass     | varchar(255)          | NO   |     | 0       |                |
| name           | varchar(255)          | NO   |     |         |                |
| title          | text                  | NO   |     | NULL    |                |
| classname      | varchar(255)          | NO   |     |         |                |
| summary        | text                  | NO   |     | NULL    |                |
| uid            | mediumint(8) unsigned | NO   |     | 0       |                |
| username       | varchar(255)          | NO   |     |         |                |
| styleid        | smallint(6) unsigned  | NO   |     | 0       |                |
| blockstyle     | text                  | NO   |     | NULL    |                |
| picwidth       | smallint(6) unsigned  | NO   |     | 0       |                |
| picheight      | smallint(6) unsigned  | NO   |     | 0       |                |
| target         | varchar(255)          | NO   |     |         |                |
| dateformat     | varchar(255)          | NO   |     |         |                |
| dateuformat    | tinyint(1)            | NO   |     | 0       |                |
| script         | varchar(255)          | NO   |     |         |                |
| param          | text                  | NO   |     | NULL    |                |
| shownum        | smallint(6) unsigned  | NO   |     | 0       |                |
| cachetime      | int(10)               | NO   |     | 0       |                |
| cachetimerange | char(5)               | NO   |     |         |                |
| punctualupdate | tinyint(1)            | NO   |     | 0       |                |
| hidedisplay    | tinyint(1)            | NO   |     | 0       |                |
| dateline       | int(10) unsigned      | NO   |     | 0       |                |
| notinherited   | tinyint(1)            | NO   |     | 0       |                |
| isblank        | tinyint(1)            | NO   |     | 0       |                |
+----------------+-----------------------+------+-----+---------+----------------+
26 rows in set (0.00 sec)

　　

3.MODIFY COLUMN

除了重命名外能够做CHANGE COLUMN能做的一切工作。

3.1用法

ALTER TABLE MyTable MODIFY COLUMN foo VARCHAR(32) NOT NULL AFTER baz;