sql alter 修改字段类型与名称的方法

ALTER TABLE "table_name"
[改变方式]

加一个栏位: ADD "栏位 1" "栏位 1 资料种类"

mysql教程> CREATE TABLE Employee(
    ->     id            int,
    ->     first_name    VARCHAR(15),
    ->     last_name     VARCHAR(15),
    ->     start_date    DATE,
    ->     end_date      DATE,
    ->     salary        FLOAT(8,2),
    ->     city          VARCHAR(10),
    ->     description   VARCHAR(15)
    -> );
Query OK, 0 rows affected (0.03 sec)

mysql>
mysql>
mysql> ALTER TABLE employee
    -> CHANGE First_Name FirstName VARCHAR(20);
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql>
mysql> DESCRIBE employee;
+-------------+-------------+------+-----+---------+-------+
| Field       | Type        | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+-------+
| id          | int(11)     | YES |     | NULL    |       |
| FirstName   | varchar(20) | YES |     | NULL    |       |
| last_name   | varchar(15) | YES |     | NULL    |       |
| start_date | date        | YES |     | NULL    |       |
| end_date    | date        | YES |     | NULL    |       |
| salary      | float(8,2) | YES |     | NULL    |       |
| city        | varchar(10) | YES |     | NULL    |       |
| description | varchar(15) | YES |     | NULL    |       |
+-------------+-------------+------+-----+---------+-------+
8 rows in set (0.01 sec)

修改字段为varchar类型

mysql> ALTER TABLE employee
-> CHANGE Last_Name Last_Name VARCHAR(50);
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0

给个字段加个索引

mysql> ALTER TABLE myTable
-> ADD UNIQUE (OrderID, ModelID);
Query OK, 0 rows affected (0.06 sec)

补充：数据库,mysql教程