mysql sql給表增加新字段的實現方法

如需在表中添加列，請使用下列語法:

ALTER TABLE table_name
ADD column_name datatype
要刪除表中的列，請使用下列語法：

ALTER TABLE table_name
DROP COLUMN column_name
注釋：某些數據庫教程系統不允許這種在數據庫表中刪除列的方式 (DROP COLUMN column_name)

。

實例
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 (0.02 sec)

mysql>
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,  

salary,  City,       Description)
    ->              values (1,'Jason',    'Martin',  '19960725',  '20060725',

1234.56, 'Toronto',  'Programmer');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,  

salary,  City,       Description)
    ->               values(2,'Alison',   'Mathews',  '19760321', '19860221',

6661.78, 'Vancouver','Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,  

salary,  City,       Description)
    ->               values(3,'James',    'Smith',    '19781212', '19900315',

6544.78, 'Vancouver','Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,  

salary,  City,       Description)
    ->               values(4,'Celia',    'Rice',     '19821024', '19990421',

2344.78, 'Vancouver','Manager');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,  

salary,  City,       Description)
    ->               values(5,'Robert',   'Black',    '19840115', '19980808',

2334.78, 'Vancouver','Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,  

salary,  City,       Description)
    ->               values(6,'Linda',    'Green',    '19870730', '19960104',

4322.78,'New York',  'Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,  

salary,  City,       Description)
    ->               values(7,'David',    'Larry',    '19901231', '19980212',

7897.78,'New York',  'Manager');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,  

salary,  City,       Description)
    ->               values(8,'James',    'Cat',     '19960917',  '20020415',

1232.78,'Vancouver', 'Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> select * from Employee;
+------+------------+-----------+------------+------------+---------+-----------

+-------------+
| id   | first_name | last_name | start_date | end_date   | salary  | city      |

description |
+------+------------+-----------+------------+------------+---------+-----------

+-------------+
|    1 | Jason      | Martin    | 1996-07-25 | 2006-07-25 | 1234.56 | Toronto   |

Programmer  |
|    2 | Alison     | Mathews   | 1976-03-21 | 1986-02-21 | 6661.78 | Vancouver |

Tester      |
|    3 | James      | Smith     | 1978-12-12 | 1990-03-15 | 6544.78 | Vancouver |

Tester      |
|    4 | Celia      | Rice      | 1982-10-24 | 1999-04-21 | 2344.78 | Vancouver |

Manager     |
|    5 | Robert     | Black     | 1984-01-15 | 1998-08-08 | 2334.78 | Vancouver |

Tester      |
|    6 | Linda      | Green     | 1987-07-30 | 1996-01-04 | 4322.78 | New York  |

Tester      |
|    7 | David      | Larry     | 1990-12-31 | 1998-02-12 | 7897.78 | New York  |

Manager     |
|    8 | James      | Cat       | 1996-09-17 | 2002-04-15 | 1232.78 | Vancouver |

Tester      |
+------+------------+-----------+------------+------------+---------+-----------

+-------------+
8 rows in set (0.00 sec)

mysql>
mysql>
mysql>
mysql> desc employee;
+-------------+-------------+------+-----+---------+-------+
| Field       | Type        | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+-------+
| id          | int(11)     | YES  |     | NULL    |       |
| first_name  | varchar(15) | 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 (0.03 sec)

mysql>
mysql> ALTER TABLE employee
    -> ADD new_date date;
Query OK, 8 rows affected (0.16 sec)
Records: 8  Duplicates: 0  Warnings: 0

mysql>
mysql> Describe employee;
+-------------+-------------+------+-----+---------+-------+
| Field       | Type        | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+-------+
| id          | int(11)     | YES  |     | NULL    |       |
| first_name  | varchar(15) | 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    |       |
| new_date    | date        | YES  |     | NULL    |       |
+-------------+-------------+------+-----+---------+-------+
9 rows in set (0.06 sec)

mysql>
mysql> SELECT ID, new_date FROM employee;
+------+----------+
| ID   | new_date |
+------+----------+
|    1 | NULL     |
|    2 | NULL     |
|    3 | NULL     |
|    4 | NULL     |
|    5 | NULL     |
|    6 | NULL     |
|    7 | NULL     |
|    8 | NULL     |
+------+----------+
8 rows in set (0.00 sec)

實例二，用上表

mysql> ALTER TABLE employee ADD Middle_Name VARCHAR(30);
Query OK, 8 rows affected (0.02 sec)
Records: 8  Duplicates: 0  Warnings: 0

mysql>
mysql> select * from Employee;
+------+------------+-----------+------------+------------+---------+-----------

+-------------+-------------+
| id   | first_name | last_name | start_date | end_date   | salary  | city      |

description | Middle_Name |
+------+------------+-----------+------------+------------+---------+-----------

+-------------+-------------+
|    1 | Jason      | Martin    | 1996-07-25 | 2006-07-25 | 1234.56 | Toronto   |

Programmer  | NULL        |
|    2 | Alison     | Mathews   | 1976-03-21 | 1986-02-21 | 6661.78 | Vancouver |

Tester      | NULL        |
|    3 | James      | Smith     | 1978-12-12 | 1990-03-15 | 6544.78 | Vancouver |

Tester      | NULL        |
|    4 | Celia      | Rice      | 1982-10-24 | 1999-04-21 | 2344.78 | Vancouver |

Manager     | NULL        |
|    5 | Robert     | Black     | 1984-01-15 | 1998-08-08 | 2334.78 | Vancouver |

Tester      | NULL        |
|    6 | Linda      | Green     | 1987-07-30 | 1996-01-04 | 4322.78 | New York  |

Tester      | NULL        |
|    7 | David      | Larry     | 1990-12-31 | 1998-02-12 | 7897.78 | New York  |

Manager     | NULL        |
|    8 | James      | Cat       | 1996-09-17 | 2002-04-15 | 1232.78 | Vancouver |

Tester      | NULL        |
+------+------------+-----------+------------+------------+---------+-----------

+-------------+-------------+
8 rows in set (0.00 sec)

mysql>
mysql> desc employee;
+-------------+-------------+------+-----+---------+-------+
| Field       | Type        | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+-------+
| id          | int(11)     | YES  |     | NULL    |       |
| first_name  | varchar(15) | 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    |       |
| Middle_Name | varchar(30) | YES  |     | NULL    |       |
+-------------+-------------+------+-----+---------+-------+
9 rows in set (0.02 sec)