对Mysql数据表本身进行操作

　　创建实验环境

mysql> create database test_db;
Query OK, 1 row affected (0.00 sec)

mysql> use test_db;
Database changed
mysql> create table test_table(id int(10),name varchar(20),age int);
Query OK, 0 rows affected (0.04 sec)

(1).查看表结构

　　查看表结构有四种方法，如果查找的不是当前数据库里的表，一定要使用[数据库名].[表名]的格式使用。最常用的一般是desc [表名]。

mysql> desc test_table;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(10)     | YES  |     | NULL    |       |
| name  | varchar(20) | YES  |     | NULL    |       |
| age   | int(11)     | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.01 sec)

mysql> explain test_table;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(10)     | YES  |     | NULL    |       |
| name  | varchar(20) | YES  |     | NULL    |       |
| age   | int(11)     | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> show columns from test_table;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(10)     | YES  |     | NULL    |       |
| name  | varchar(20) | YES  |     | NULL    |       |
| age   | int(11)     | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> show fields from test_table;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(10)     | YES  |     | NULL    |       |
| name  | varchar(20) | YES  |     | NULL    |       |
| age   | int(11)     | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

(2).修改表名

　　alter table [旧的表名] rename [新的表名];

　　如果不在当前数据库，需要使用[数据库名].[表名]代替单一的[表名]。

mysql> alter table test_table rename table_newname;
Query OK, 0 rows affected (0.04 sec)

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

(3).只修改表的字段类型

　　alter tabel [表名] modify [字段名] [修改后的字段类型];

　　如果不在当前数据库，需要使用[数据库名].[表名]代替单一的[表名]。

　　修改已有数据的表的字段类型，请谨慎。

mysql> desc table_newname;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(10)     | YES  |     | NULL    |       |
| name  | varchar(20) | YES  |     | NULL    |       |
| age   | int(11)     | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> alter table table_newname modify name char(22);
Query OK, 0 rows affected (0.07 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc table_newname;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id    | int(10)  | YES  |     | NULL    |       |
| name  | char(22) | YES  |     | NULL    |       |
| age   | int(11)  | YES  |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
3 rows in set (0.00 sec)

(4).修改表的字段名和字段类型

　　alter table [表名] change [旧的字段名] [新的字段名] [新的字段类型];

　　如果不在当前数据库，需要使用[数据库名].[表名]代替单一的[表名]。

　　修改已有数据的表的字段类型，请谨慎。如果不想修改字段类型，请保持类型的一致。

mysql> desc table_newname;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id    | int(10)  | YES  |     | NULL    |       |
| name  | char(22) | YES  |     | NULL    |       |
| age   | int(11)  | YES  |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> alter table table_newname change name newname char(30);
Query OK, 0 rows affected (0.07 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc table_newname;
+---------+----------+------+-----+---------+-------+
| Field   | Type     | Null | Key | Default | Extra |
+---------+----------+------+-----+---------+-------+
| id      | int(10)  | YES  |     | NULL    |       |
| newname | char(30) | YES  |     | NULL    |       |
| age     | int(11)  | YES  |     | NULL    |       |
+---------+----------+------+-----+---------+-------+
3 rows in set (0.00 sec)

(5).添加字段

　　alter table [表名] add [字段名] [字段类型];

　　如果不在当前数据库，需要使用[数据库名].[表名]代替单一的[表名]。

mysql> desc table_newname;
+---------+----------+------+-----+---------+-------+
| Field   | Type     | Null | Key | Default | Extra |
+---------+----------+------+-----+---------+-------+
| id      | int(10)  | YES  |     | NULL    |       |
| newname | char(30) | YES  |     | NULL    |       |
| age     | int(11)  | YES  |     | NULL    |       |
+---------+----------+------+-----+---------+-------+
3 rows in set (0.01 sec)

mysql> alter table table_newname add job char(40);
Query OK, 0 rows affected (0.13 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc table_newname;
+---------+----------+------+-----+---------+-------+
| Field   | Type     | Null | Key | Default | Extra |
+---------+----------+------+-----+---------+-------+
| id      | int(10)  | YES  |     | NULL    |       |
| newname | char(30) | YES  |     | NULL    |       |
| age     | int(11)  | YES  |     | NULL    |       |
| job     | char(40) | YES  |     | NULL    |       |
+---------+----------+------+-----+---------+-------+
4 rows in set (0.00 sec)

(6).在表的指定位置添加字段

　　字段添加到第一位：alter table [表名] add [字段名] [字段类型] first;

　　字段添加到某一位的后面：alter table [表名] add [字段名] [字段类型] after [字段名];

　　如果不在当前数据库，需要使用[数据库名].[表名]代替单一的[表名]。

mysql> desc table_newname;
+---------+----------+------+-----+---------+-------+
| Field   | Type     | Null | Key | Default | Extra |
+---------+----------+------+-----+---------+-------+
| id      | int(10)  | YES  |     | NULL    |       |
| newname | char(30) | YES  |     | NULL    |       |
| age     | int(11)  | YES  |     | NULL    |       |
| job     | char(40) | YES  |     | NULL    |       |
+---------+----------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql> alter table table_newname add sex enum('M','W') first;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table table_newname add address varchar(40) after newname;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc table_newname;
+---------+---------------+------+-----+---------+-------+
| Field   | Type          | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| sex     | enum('M','W') | YES  |     | NULL    |       |
| id      | int(10)       | YES  |     | NULL    |       |
| newname | char(30)      | YES  |     | NULL    |       |
| address | varchar(40)   | YES  |     | NULL    |       |
| age     | int(11)       | YES  |     | NULL    |       |
| job     | char(40)      | YES  |     | NULL    |       |
+---------+---------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

(7).删除表的指定字段

　　alter table [表名] drop [字段名];

　　如果不在当前数据库，需要使用[数据库名].[表名]代替单一的[表名]。

mysql> desc table_newname;
+---------+---------------+------+-----+---------+-------+
| Field   | Type          | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| sex     | enum('M','W') | YES  |     | NULL    |       |
| id      | int(10)       | YES  |     | NULL    |       |
| newname | char(30)      | YES  |     | NULL    |       |
| address | varchar(40)   | YES  |     | NULL    |       |
| age     | int(11)       | YES  |     | NULL    |       |
| job     | char(40)      | YES  |     | NULL    |       |
+---------+---------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

mysql> alter table table_newname drop sex;
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc table_newname;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id      | int(10)     | YES  |     | NULL    |       |
| newname | char(30)    | YES  |     | NULL    |       |
| address | varchar(40) | YES  |     | NULL    |       |
| age     | int(11)     | YES  |     | NULL    |       |
| job     | char(40)    | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

　　

　　如果还有其他的操作，以后再加