mysql sql给表增加新字段的实现方法
如需在表中添加列，请使用下列语法:
ALTER TABLE table_name
ADD column_name datatype
要删除表中的列，请使用下列语法：
ALTER TABLE table_name
DROP COLUMN column_name
注释：某些数据库教程系统不允许这种在数据库表中删除列的方式 (DROP COLUMN column_name)
。
实例
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)
实例二，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)
补充：数据库,mysql教程
