为了学习数据库，先熟悉一下sql语言，也就以mysql为例子开始学习了！

（参考书籍《深入浅出mysql 数据库开发、优化、管理维护》）

下边是执行的sql语句，主要是建立表和修改表：

首先进入windows命令提示符下：

Microsoft Windows XP [版本 5.1.2600]
(C) 版权所有 1985-2001 Microsoft Corp.

C:\Documents and Settings\Administrator>mysql -uroot -proot
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.1.41-community MySQL Community Server (GPL)

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| test |
+--------------------+
3 rows in set (0.02 sec)

mysql> use test;
Database changed
mysql> create table emp(ename varchar(20) not null primary key,hirdate date,sal
decimal(10,2),deptno int(2));
Query OK, 0 rows affected (0.08 sec)

mysql> desc emp;
+---------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| ename | varchar(20) | NO | PRI | NULL | |
| hirdate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+---------+---------------+------+-----+---------+-------+
4 rows in set (0.02 sec)

mysql> show create table emp;
+-------+-----------------------------------------------------------------------
--------------------------------------------------------------------------------
-----------------------------------------------------------------+
| Table | Create Table

|
+-------+-----------------------------------------------------------------------
--------------------------------------------------------------------------------
-----------------------------------------------------------------+
| emp | CREATE TABLE `emp` (
`ename` varchar(20) NOT NULL,
`hirdate` date DEFAULT NULL,
`sal` decimal(10,2) DEFAULT NULL,
`deptno` int(2) DEFAULT NULL,
PRIMARY KEY (`ename`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-----------------------------------------------------------------------
--------------------------------------------------------------------------------
-----------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> alter table emp modify ename varchar(30);
Query OK, 0 rows affected (0.19 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc emp;
+---------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| ename | varchar(30) | NO | PRI | | |
| hirdate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+---------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql> alter table emp add column age int(3);
Query OK, 0 rows affected (0.19 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc emp;
+---------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| ename | varchar(30) | NO | PRI | | |
| hirdate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
| age | int(3) | YES | | NULL | |
+---------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql> alter table emp change age agenum int(4);
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc emp;
+---------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| ename | varchar(30) | NO | PRI | | |
| hirdate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
| agenum | int(4) | YES | | NULL | |
+---------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql> alter table emp drop agenum;
Query OK, 0 rows affected (0.17 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc emp;
+---------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| ename | varchar(30) | NO | PRI | | |
| hirdate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+---------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql> alter table emp add column birth date after ename;
Query OK, 0 rows affected (0.16 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc emp;
+---------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| ename | varchar(30) | NO | PRI | | |
| birth | date | YES | | NULL | |
| hirdate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+---------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql> alter table emp modify sal first;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use near 'first
' at line 1
mysql> alter table emp modify sal decimal(10,2) first;
Query OK, 0 rows affected (0.16 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc emp;
+---------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| sal | decimal(10,2) | YES | | NULL | |
| ename | varchar(30) | NO | PRI | | |
| birth | date | YES | | NULL | |
| hirdate | date | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+---------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql> alter table emp change ename name varchar(20) first;
Query OK, 0 rows affected (0.16 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc emp;
+---------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| name | varchar(20) | NO | PRI | | |
| sal | decimal(10,2) | YES | | NULL | |
| birth | date | YES | | NULL | |
| hirdate | date | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+---------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql> alter table emp change birth birthday date after hirdate;
Query OK, 0 rows affected (0.23 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| name | varchar(20) | NO | PRI | | |
| sal | decimal(10,2) | YES | | NULL | |
| hirdate | date | YES | | NULL | |
| birthday | date | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql> alter table emp rename emptable;
Query OK, 0 rows affected (0.22 sec)

mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| emptable |
+----------------+
1 row in set (0.00 sec)

mysql> drop table emptable;
Query OK, 0 rows affected (0.06 sec)

mysql> show tables;
Empty set (0.00 sec)

mysql> exit;
Bye

C:\Documents and Settings\Administrator>