添加主键约束 唯一约束 无更改INNoDB

mysql> CREATE TABLE users2(
    -> username VARCHAR(10) NOT NULL
    -> ,
    -> pid SMALLINT UNSIGNED
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql> SHOW CREATE TABLE users2;
+--------+----------------------------------------------------------------------
---------------------------------------------------------------------+
| Table  | Create Table
                                                                     |
+--------+----------------------------------------------------------------------
---------------------------------------------------------------------+
| users2 | CREATE TABLE `users2` (
  `username` varchar(10) NOT NULL,
  `pid` smallint(5) unsigned DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8 |
+--------+----------------------------------------------------------------------
---------------------------------------------------------------------+
1 row in set (0.01 sec)

mysql> ALTER TABLE users2 ADD id SMALLINT UNSIGNED ;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users2;
+----------+----------------------+------+-----+---------+-------+
| Field    | Type                 | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10)          | NO   |     | NULL    |       |
| pid      | smallint(5) unsigned | YES  |     | NULL    |       |
| id       | smallint(5) unsigned | YES  |     | NULL    |       |
+----------+----------------------+------+-----+---------+-------+
3 rows in set (0.03 sec)

mysql> ALTER TABLE users2 ADD CONSTRAINT PK_users2_id PRIMARY KEY (id);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users2;
+----------+----------------------+------+-----+---------+-------+
| Field    | Type                 | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10)          | NO   |     | NULL    |       |
| pid      | smallint(5) unsigned | YES  |     | NULL    |       |
| id       | smallint(5) unsigned | NO   | PRI | 0       |       |
+----------+----------------------+------+-----+---------+-------+
3 rows in set (0.03 sec)

                                                添加唯一约束；
mysql> ALTER TABLE users2 ADD UNIQUE (username);
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW CREATE TABLE users2;
+--------+----------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
-------------------+
| Table  | Create Table


                   |
+--------+----------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
-------------------+
| users2 | CREATE TABLE `users2` (
  `username` varchar(10) NOT NULL,
  `pid` smallint(5) unsigned DEFAULT NULL,
  `id` smallint(5) unsigned NOT NULL DEFAULT '0',
  PRIMARY KEY (`id`),
  UNIQUE KEY `username` (`username`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 |
+--------+----------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
-------------------+
1 row in set (0.01 sec)

                                                       添加外键约束 
mysql> ALTER TABLE users2 ADD FOREIGN KEY (Pid) REFERENCES provinces(id);
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW CREATE TABLE users2;
+--------+----------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
----------------------------------------+
| Table  | Create Table


                                        |
+--------+----------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
----------------------------------------+
| users2 | CREATE TABLE `users2` (
  `username` varchar(10) NOT NULL,
  `pid` smallint(5) unsigned DEFAULT NULL,
  `id` smallint(5) unsigned NOT NULL DEFAULT '0',
  PRIMARY KEY (`id`),
  UNIQUE KEY `username` (`username`),
  KEY `pid` (`pid`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 |
+--------+----------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
----------------------------------------+
1 row in set (0.00 sec)

                                                        添加 删除；
mysql> SHOW COLUMNS FROM users2;
+----------+----------------------+------+-----+---------+-------+
| Field    | Type                 | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10)          | NO   | UNI | NULL    |       |
| pid      | smallint(5) unsigned | YES  | MUL | NULL    |       |
| id       | smallint(5) unsigned | NO   | PRI | 0       |       |
| age      | tinyint(3) unsigned  | NO   |     | NULL    |       |
+----------+----------------------+------+-----+---------+-------+
4 rows in set (0.03 sec)

mysql> ALTER TABLE users2 ALTER age SET DEFAULT 15;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users2;
+----------+----------------------+------+-----+---------+-------+
| Field    | Type                 | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10)          | NO   | UNI | NULL    |       |
| pid      | smallint(5) unsigned | YES  | MUL | NULL    |       |
| id       | smallint(5) unsigned | NO   | PRI | 0       |       |
| age      | tinyint(3) unsigned  | NO   |     | 15      |       |
+----------+----------------------+------+-----+---------+-------+
4 rows in set (0.02 sec)

mysql> ALTER TABLE users2 ALTER age DROP DEFAULT;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users2;
+----------+----------------------+------+-----+---------+-------+
| Field    | Type                 | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10)          | NO   | UNI | NULL    |       |
| pid      | smallint(5) unsigned | YES  | MUL | NULL    |       |
| id       | smallint(5) unsigned | NO   | PRI | 0       |       |
| age      | tinyint(3) unsigned  | NO   |     | NULL    |       |
+----------+----------------------+------+-----+---------+-------+
4 rows in set (0.03 sec)

mysql> Bye
Ctrl-C -- exit!

D:\phpStudy\PHPTutorial\MySQL\bin>