【一步一步学习mysql】修改数据表

添加单列

ALTER TABLE tbl_name ADD [COLUMN] col_name column_definition [FIRST|AFTER col_name]

mysql> alter table users add age tinyint unsigned not null default 10;
mysql> show columns from users;
+-------+----------------------+------+-----+---------+----------------+
| Field | Type                 | Null | Key | Default | Extra          |
+-------+----------------------+------+-----+---------+----------------+
| id    | smallint(6)          | NO   | PRI | NULL    | auto_increment |
| name  | varchar(20)          | NO   |     | NULL    |                |
| pid   | smallint(5) unsigned | YES  | MUL | NULL    |                |
| age   | tinyint(3) unsigned  | NO   |     | 10      |                |
+-------+----------------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

mysql> alter table users add password varchar(20) not null after name;
mysql> show columns from users;
+----------+----------------------+------+-----+---------+----------------+
| Field    | Type                 | Null | Key | Default | Extra          |
+----------+----------------------+------+-----+---------+----------------+
| id       | smallint(6)          | NO   | PRI | NULL    | auto_increment |
| name     | varchar(20)          | NO   |     | NULL    |                |
| password | varchar(20)          | NO   |     | NULL    |                |
| pid      | smallint(5) unsigned | YES  | MUL | NULL    |                |
| age      | tinyint(3) unsigned  | NO   |     | 10      |                |
+----------+----------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

添加多列

ALTER TABLE tbl_name ADD [COLUMN] (col_name column_definition, ...)

mysql> alter table users add (weight tinyint unsigned not null, height tinyint unsigned);
mysql> show columns from users;
+----------+----------------------+------+-----+---------+----------------+
| Field    | Type                 | Null | Key | Default | Extra          |
+----------+----------------------+------+-----+---------+----------------+
| id       | smallint(6)          | NO   | PRI | NULL    | auto_increment |
| name     | varchar(20)          | NO   |     | NULL    |                |
| password | varchar(20)          | NO   |     | NULL    |                |
| pid      | smallint(5) unsigned | YES  | MUL | NULL    |                |
| age      | tinyint(3) unsigned  | NO   |     | 10      |                |
| weight   | tinyint(3) unsigned  | NO   |     | NULL    |                |
| height   | tinyint(3) unsigned  | YES  |     | NULL    |                |
+----------+----------------------+------+-----+---------+----------------+
7 rows in set (0.00 sec)

删除列

ALTER TABLE tbl_name DROP [COLUMN] col_name

mysql> ALTER TABLE users DROP weight, DROP height;
Query OK, 0 rows affected (0.40 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show columns from users;
+----------+----------------------+------+-----+---------+----------------+
| Field    | Type                 | Null | Key | Default | Extra          |
+----------+----------------------+------+-----+---------+----------------+
| id       | smallint(6)          | NO   | PRI | NULL    | auto_increment |
| name     | varchar(20)          | NO   |     | NULL    |                |
| password | varchar(20)          | NO   |     | NULL    |                |
| pid      | smallint(5) unsigned | YES  | MUL | NULL    |                |
| age      | tinyint(3) unsigned  | NO   |     | 10      |                |
+----------+----------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

添加主键约束

ALTER TABLE tbl_name ADD [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (index_col_name)

# 创建新表
mysql> CREATE TABLE users3 (id SMALLINT, name VARCHAR(20), pid SMALLINT UNSIGNED);
Query OK, 0 rows affected (0.23 sec)

mysql> SHOW COLUMNS FROM users3;
+-------+----------------------+------+-----+---------+-------+
| Field | Type                 | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+-------+
| id    | smallint(6)          | YES  |     | NULL    |       |
| name  | varchar(20)          | YES  |     | NULL    |       |
| pid   | smallint(5) unsigned | YES  |     | NULL    |       |
+-------+----------------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

# 添加主键
mysql> ALTER TABLE users3 ADD PRIMARY KEY (id);
Query OK, 0 rows affected (0.45 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users3;
+-------+----------------------+------+-----+---------+-------+
| Field | Type                 | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+-------+
| id    | smallint(6)          | NO   | PRI | NULL    |       |
| name  | varchar(20)          | YES  |     | NULL    |       |
| pid   | smallint(5) unsigned | YES  |     | NULL    |       |
+-------+----------------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

删除主键约束

ALTER TABLE tbl_name DROP PRIMARY KEY;

添加唯一约束

ALTER TABLE tlb_name ADD [CONSTRAINT [symbol]] UNIQUE [INDEX|KEY] [index_name] [index_type] (index_col_name, ...);

mysql> ALTER TABLE users3 ADD UNIQUE KEY (name);
Query OK, 0 rows affected (0.25 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users3;
+-------+----------------------+------+-----+---------+-------+
| Field | Type                 | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+-------+
| id    | smallint(6)          | NO   | PRI | NULL    |       |
| name  | varchar(20)          | YES  | UNI | NULL    |       |
| pid   | smallint(5) unsigned | YES  |     | NULL    |       |
+-------+----------------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

删除唯一约束

ALTER TABLE tbl_name DROP {INDEX|KEY} index_name;

注意：这边存在index_name是因为可以存在多个唯一约束。故我们应该先学会怎么查看约束的名称。

mysql> SHOW INDEXES FROM users3G;
*************************** 1. row ***************************
        Table: users3
   Non_unique: 0
     Key_name: PRIMARY
 Seq_in_index: 1
  Column_name: id
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null: 
   Index_type: BTREE
      Comment: 
Index_comment: 
*************************** 2. row ***************************
        Table: users3
   Non_unique: 0
     Key_name: name
 Seq_in_index: 1
  Column_name: name
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null: YES
   Index_type: BTREE
      Comment: 
Index_comment: 
*************************** 3. row ***************************
        Table: users3
   Non_unique: 1
     Key_name: pid
 Seq_in_index: 1
  Column_name: pid
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null: YES
   Index_type: BTREE
      Comment: 
Index_comment: 
3 rows in set (0.00 sec)

# 我们想删除name字段上的index，可以看到该字段的index名字为name
mysql> ALTER TABLE users3 DROP INDEX name;
Query OK, 0 rows affected (0.19 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW INDEXES FROM users3G;
*************************** 1. row ***************************
        Table: users3
   Non_unique: 0
     Key_name: PRIMARY
 Seq_in_index: 1
  Column_name: id
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null: 
   Index_type: BTREE
      Comment: 
Index_comment: 
*************************** 2. row ***************************
        Table: users3
   Non_unique: 1
     Key_name: pid
 Seq_in_index: 1
  Column_name: pid
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null: YES
   Index_type: BTREE
      Comment: 
Index_comment: 
2 rows in set (0.00 sec)

mysql> SHOW COLUMNS FROM users3;
+-------+----------------------+------+-----+---------+-------+
| Field | Type                 | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+-------+
| id    | smallint(6)          | NO   | PRI | NULL    |       |
| name  | varchar(20)          | YES  |     | NULL    |       |
| pid   | smallint(5) unsigned | YES  | MUL | NULL    |       |
| age   | int(11)              | YES  |     | NULL    |       |
+-------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

添加外键约束

ALTER TABLE tbl_name ADD [CONSTRAINT [symbol]] FOREIGN KEY [index_name] (index_col_name, ...) REFERENCES reference_definition;

mysql> ALTER TABLE users3 ADD FOREIGN KEY (pid) REFERENCES province(id);
Query OK, 0 rows affected (0.62 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> SHOW COLUMNS FROM users3;
+-------+----------------------+------+-----+---------+-------+
| Field | Type                 | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+-------+
| id    | smallint(6)          | NO   | PRI | NULL    |       |
| name  | varchar(20)          | YES  | UNI | NULL    |       |
| pid   | smallint(5) unsigned | YES  | MUL | NULL    |       |
+-------+----------------------+------+-----+---------+-------+
3 rows in set (0.01 sec)

mysql> SHOW CREATE TABLE users3;
+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table  | Create Table                                                                                                                                                                                                                                                                                                                   |
+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| users3 | CREATE TABLE `users3` (
  `id` smallint(6) NOT NULL,
  `name` varchar(20) DEFAULT NULL,
  `pid` smallint(5) unsigned DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `name` (`name`),
  KEY `pid` (`pid`),
  CONSTRAINT `users3_ibfk_1` FOREIGN KEY (`pid`) REFERENCES `province` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

删除外键约束

ALTER TABLE tbl_name DROP FOREIGN KEY fk_symbol;

注意：这个fk_symbol可以在上面的 SHOW CREATE TABLE users3;中可以看到，为users3_ibfk_1。

mysql> SHOW CREATE TABLE users3;
+--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table  | Create Table                                                                                                                                                                                                                                                                                                      |
+--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| users3 | CREATE TABLE `users3` (
  `id` smallint(6) NOT NULL,
  `name` varchar(20) DEFAULT NULL,
  `pid` smallint(5) unsigned DEFAULT NULL,
  `age` int(11),
  PRIMARY KEY (`id`),
  KEY `pid` (`pid`),
  CONSTRAINT `users3_ibfk_1` FOREIGN KEY (`pid`) REFERENCES `province` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> ALTER TABLE users3 DROP FOREIGN KEY users3_ibfk_1;
Query OK, 0 rows affected (0.11 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW CREATE TABLE users3;
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table  | Create Table                                                                                                                                                                                                                       |
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| users3 | CREATE TABLE `users3` (
  `id` smallint(6) NOT NULL,
  `name` varchar(20) DEFAULT NULL,
  `pid` smallint(5) unsigned DEFAULT NULL,
  `age` int(11),
  PRIMARY KEY (`id`),
  KEY `pid` (`pid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

添加删除默认约束

ALTER TABLE tbl_name ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT};

mysql> SHOW COLUMNS FROM users3;
+-------+----------------------+------+-----+---------+-------+
| Field | Type                 | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+-------+
| id    | smallint(6)          | NO   | PRI | NULL    |       |
| name  | varchar(20)          | YES  | UNI | NULL    |       |
| pid   | smallint(5) unsigned | YES  | MUL | NULL    |       |
| age   | int(11)              | YES  |     | NULL    |       |
+-------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql> ALTER TABLE users3 ALTER age SET DEFAULT 15;
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users3;
+-------+----------------------+------+-----+---------+-------+
| Field | Type                 | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+-------+
| id    | smallint(6)          | NO   | PRI | NULL    |       |
| name  | varchar(20)          | YES  | UNI | NULL    |       |
| pid   | smallint(5) unsigned | YES  | MUL | NULL    |       |
| age   | int(11)              | YES  |     | 15      |       |
+-------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql> ALTER TABLE users3 ALTER age DROP DEFAULT;
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users3;
+-------+----------------------+------+-----+---------+-------+
| Field | Type                 | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+-------+
| id    | smallint(6)          | NO   | PRI | NULL    |       |
| name  | varchar(20)          | YES  | UNI | NULL    |       |
| pid   | smallint(5) unsigned | YES  | MUL | NULL    |       |
| age   | int(11)              | YES  |     | NULL    |       |
+-------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

修改数据表

• 修改列定义

ALTER TABLE tbl_name MODIFY [COLUMN] col_name column_definition [FIRST|AFTER col_name];

mysql> SHOW COLUMNS FROM users3;
+-------+----------------------+------+-----+---------+-------+
| Field | Type                 | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+-------+
| id    | smallint(6)          | NO   | PRI | NULL    |       |
| name  | varchar(20)          | YES  |     | NULL    |       |
| pid   | smallint(5) unsigned | YES  | MUL | NULL    |       |
| age   | int(11)              | YES  |     | NULL    |       |
+-------+----------------------+------+-----+---------+-------+

mysql> ALTER TABLE users3 MODIFY age INT AFTER name;
Query OK, 0 rows affected (0.44 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users3;
+-------+----------------------+------+-----+---------+-------+
| Field | Type                 | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+-------+
| id    | smallint(6)          | NO   | PRI | NULL    |       |
| name  | varchar(20)          | YES  |     | NULL    |       |
| age   | int(11)              | YES  |     | NULL    |       |
| pid   | smallint(5) unsigned | YES  | MUL | NULL    |       |
+-------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

• 修改列名称

ALTER TABLE tbl_name CHANGE [COLUMN] old_col_name new_col_name column_definition [FIRST|AFTER col_name];

mysql> ALTER TABLE users3 CHANGE pid province_id SMALLINT UNSIGNED;
Query OK, 0 rows affected (0.10 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users3;
+-------------+----------------------+------+-----+---------+-------+
| Field       | Type                 | Null | Key | Default | Extra |
+-------------+----------------------+------+-----+---------+-------+
| id          | smallint(6)          | NO   | PRI | NULL    |       |
| name        | varchar(20)          | YES  |     | NULL    |       |
| age         | int(11)              | YES  |     | NULL    |       |
| province_id | smallint(5) unsigned | YES  | MUL | NULL    |       |
+-------------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

• 修改数据表名称

# 方法1
ALTER TABLE tbl_name RENAME [TO|AS] new_tbl_name;
# 方法2
RENAME TABLE tbl_name TO new_tbl_name [,tbl_name2 TO new_tbl_name2] ...

mysql> ALTER TABLE users3 RENAME TO users33;

mysql> RENAME TABLE users2 TO users22, users TO users11;