15-1 庫和表相關操做

一 庫相關操做：
0建立數據庫：
 語法(help create database)

CREATE DATABASE 數據庫名 charset utf8;

1 查看數據庫
show databases;
show create database db1;
select database();

2 選擇數據庫
USE 數據庫名

3 刪除數據庫
DROP DATABASE 數據庫名;

4 修改數據庫
alter database db1 charset utf8;

二 表相關操做
建立表：
#語法：
create table 表名(
字段名1 類型[(寬度) 約束條件],
字段名2 類型[(寬度) 約束條件],
字段名3 類型[(寬度) 約束條件]
);

#注意：
1. 在同一張表中，字段名是不能相同
2. 寬度和約束條件可選
3. 字段名和類型是必須的

例子一：

1 建立表
create table t1(id int,name varchar(50),sex enum('male','female'),age int(3));
表中插入數據
insert into t1 values(1,'egon','male',18),(2,'alex','female',81); 順序要和表結構一致

查看錶結構

 1 mysql> describe t1;
 2 +-------+-----------------------+------+-----+---------+-------+
 3 | Field | Type                  | Null | Key | Default | Extra |
 4 +-------+-----------------------+------+-----+---------+-------+
 5 | id    | int(11)               | YES  |     | NULL    |       |
 6 | name  | varchar(50)           | YES  |     | NULL    |       |
 7 | sex   | enum('male','female') | YES  |     | NULL    |       |
 8 | age   | int(3)                | YES  |     | NULL    |       |
 9 +-------+-----------------------+------+-----+---------+-------+
10 4 rows in set (0.00 sec)

 

show create table t1\G; #查看錶詳細結構，可加\G

2 修改表ALTER TABLE

      ALTER TABLE 表名   RENAME 新表名;
                         

例子：  alter table t1 rename t2;


3 增長表字段：（不能和原來的重複）                

 1 mysql> alter table student10 add name varchar(20) not null,add age int(3) not null default 22;
 2 Query OK, 0 rows affected (1.06 sec)
 3 Records: 0  Duplicates: 0  Warnings: 0
 4 
 5 mysql> describe student10;
 6 +-------+-------------+------+-----+---------+-------+
 7 | Field | Type        | Null | Key | Default | Extra |
 8 +-------+-------------+------+-----+---------+-------+
 9 | id    | int(11)     | YES  |     | NULL    |       |
10 | name  | varchar(20) | NO   |     | NULL    |       |
11 | age   | int(3)      | NO   |     | 22      |       |
12 +-------+-------------+------+-----+---------+-------+
13 3 rows in set (0.00 sec)

4 在name字段以後添加一個class字段

 1 mysql> alter table student10 add class varchar(10) not null after name;
 2 Query OK, 0 rows affected (1.00 sec)
 3 Records: 0  Duplicates: 0  Warnings: 0
 4 
 5 mysql> describe student10;
 6 +-------+-------------+------+-----+---------+-------+
 7 | Field | Type        | Null | Key | Default | Extra |
 8 +-------+-------------+------+-----+---------+-------+
 9 | id    | int(11)     | YES  |     | NULL    |       |
10 | name  | varchar(20) | NO   |     | NULL    |       |
11 | class | varchar(10) | NO   |     | NULL    |       |
12 | age   | int(3)      | NO   |     | 22      |       |
13 +-------+-------------+------+-----+---------+-------+
14 4 rows in set (0.00 sec)

5 添加到字段最前面

 1 mysql> alter table student10 add sex enum('male','female') default 'male' first;
 2 Query OK, 0 rows affected (1.05 sec)
 3 Records: 0  Duplicates: 0  Warnings: 0
 4 
 5 mysql> describe student10;
 6 +-------+-----------------------+------+-----+---------+-------+
 7 | Field | Type                  | Null | Key | Default | Extra |
 8 +-------+-----------------------+------+-----+---------+-------+
 9 | sex   | enum('male','female') | YES  |     | male    |       |
10 | id    | int(11)               | YES  |     | NULL    |       |
11 | name  | varchar(20)           | NO   |     | NULL    |       |
12 | class | varchar(10)           | NO   |     | NULL    |       |
13 | age   | int(3)                | NO   |     | 22      |       |
14 +-------+-----------------------+------+-----+---------+-------+
15 5 rows in set (0.00 sec)

6 刪除字段
mysql> alter table student10 drop sex;
Query OK, 0 rows affected (0.97 sec)
Records: 0  Duplicates: 0  Warnings: 0

7 修改字段 modify
例子一：

 1 mysql> alter table student10 modify age int(5);
 2 Query OK, 0 rows affected (1.21 sec)
 3 Records: 0  Duplicates: 0  Warnings: 0
 4 
 5 mysql> describe student10;
 6 +-------+-------------+------+-----+---------+-------+
 7 | Field | Type        | Null | Key | Default | Extra |
 8 +-------+-------------+------+-----+---------+-------+
 9 | id    | int(11)     | YES  |     | NULL    |       |
10 | name  | varchar(20) | NO   |     | NULL    |       |
11 | class | varchar(10) | NO   |     | NULL    |       |
12 | age   | int(5)      | YES  |     | NULL    |       |
13 +-------+-------------+------+-----+---------+-------+
14 4 rows in set (0.00 sec)

 

例子二：

mysql> alter table student10 modify id int(11) not null primary key auto_increment;
Query OK, 0 rows affected (1.22 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> describe student10;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int(11)     | NO   | PRI | NULL    | auto_increment |
| name  | varchar(20) | NO   |     | NULL    |                |
| class | varchar(10) | NO   |     | NULL    |                |
| age   | int(5)      | YES  |     | NULL    |                |
+-------+-------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)

 

8. 對已經存在的表增長複合主鍵
mysql> alter table service2
    -> add primary key(host_ip,port);        

9. 增長主鍵
mysql> alter table student1
    -> modify name varchar(10) not null primary key;

10. 增長主鍵和自動增加
mysql> alter table student1
    -> modify id int not null primary key auto_increment;
11. 刪除主鍵
a. 刪除自增約束
mysql> alter table student10 modify id int(11) not null; 

b. 刪除主鍵
mysql> alter table student10                                 
    -> drop primary key;
    
12 複製表
複製表結構＋記錄 （key不會複製: 主鍵、外鍵和索引

mysql> create table new_hu select * from department;
Query OK, 2 rows affected (0.77 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from new_hu;
+-------+-----------------------------------+
| id    | name                              |
+-------+-----------------------------------+
|     1 | 歐德博愛技術有限事業部            |
| 22222 | 艾利克斯人力資源部                |
+-------+-----------------------------------+
2 rows in set (0.00 sec)
只複製表結構：用like
mysql> create table t10 like department;
Query OK, 0 rows affected (0.66 sec)

mysql> select * from t10;
Empty set (0.01 sec)

13  刪除表DROP TABLE 表名;