mysqlsql语句学习（一）

     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！

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（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>