MySQL（一）庫和表的基本操作 DDL

主要介紹數據定義語言DDL

• CREATE
• DROP
• ALTER

一、登入數據庫

1、本地登錄

[root@localhost ~]# mysql -uroot -p 
Enter password:

2、遠程客戶端登錄（-h：mysql服務器IP地址）

[root@client ~]# mysql -h192.168.14.212 -uroot -p
Enter password:

3、修改登錄密碼

1、mysql>SET PASSWORD FOR 'USERNAME'@'HOST'=PASSWORD('new_password');
	SET PASSWORD FOR 'root'@'localhost'=PASSWORD('123456');
	FLUSH PRIVILEGES;

2、#mysqladmin -u USERNAME -h HOSTNAME password 'new_password' -p

3、mysql>UPDATE user SET Passwrod=PASSWORD('new_password') WHERE USER='root' AND Host='127.0.0.1';
	MariaDB [mysql]> UPDATE  user SET Password=PASSWORD('123456') WHERE USER='root' AND Host='127.0.0.1';

二、庫的操作

1、創建數據庫

database後面跟新建數據庫名稱
MariaDB [(none)]> CREATE DATABASE company;

2、查看數據庫

MariaDB [(none)]> SHOW DATABASES;

3、選擇數據庫

MariaDB [(none)]> USE company;

4、刪除數據庫

MariaDB [(none)]> DROP DATABASE company;

三、表的操作

1、創建表的語法形式

MariaDB [company]> CREATE TABLE t_dept(depton INT,dname VARCHAR(20),loc VARCHAR(40));

表名：t_dept
屬性名：depton、dname、loc
數據類型：INT、VARCHAR

2、查看錶

MariaDB [company]> DESC t_dept;
+--------+-------------+------+-----+---------+-------+
| Field  | Type        | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| depton | int(11)     | YES  |     | NULL    |       |
| dname  | varchar(20) | YES  |     | NULL    |       |
| loc    | varchar(40) | YES  |     | NULL    |       |
+--------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

3、刪除表

MariaDB [company]> DROP TABLE t_dept;
Query OK, 0 rows affected (0.01 sec)

再次查看提示表不存在
MariaDB [company]> DESC t_dept;
ERROR 1146 (42S02): Table 'company.t_dept' doesn't exist

4、修改表

4.1修改表名

#ALTER TABLE 舊錶名 RENAME 新表名;
MariaDB [company]> ALTER TABLE t_dept RENAME tab_dept;

查看修改之後
MariaDB [company]> SHOW TABLES;
+-------------------+
| Tables_in_company |
+-------------------+
| tab_dept          |
+-------------------+

4.2增加字段

------------1、在表的最後一個位置添加字段------------
MariaDB [company]> ALTER TABLE tab_dept ADD descri VARCHAR(20);
Query OK, 0 rows affected (0.04 sec)               
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [company]> DESC tab_dept;
+--------+-------------+------+-----+---------+-------+
| Field  | Type        | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| depton | int(11)     | YES  |     | NULL    |       |
| dname  | varchar(20) | YES  |     | NULL    |       |
| loc    | varchar(40) | YES  |     | NULL    |       |
| descri | varchar(20) | YES  |     | NULL    |       |
+--------+-------------+------+-----+---------+-------+

------------2、在表的第一個位置添加字段------------
MariaDB [company]> ALTER TABLE tab_dept ADD descri2 VARCHAR(20) FIRST;
Query OK, 0 rows affected (0.04 sec)               
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [company]> DESC tab_dept;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| descri2 | varchar(20) | YES  |     | NULL    |       |
| depton  | int(11)     | YES  |     | NULL    |       |
| dname   | varchar(20) | YES  |     | NULL    |       |
| loc     | varchar(40) | YES  |     | NULL    |       |
| descri  | varchar(20) | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+

------------3、在表的指定字段之後添加字段------------
MariaDB [company]> ALTER TABLE tab_dept ADD descri3 VARCHAR(20) AFTER depton;
Query OK, 0 rows affected (0.04 sec)               
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [company]> DESC tab_dept;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| descri2 | varchar(20) | YES  |     | NULL    |       |
| depton  | int(11)     | YES  |     | NULL    |       |
| descri3 | varchar(20) | YES  |     | NULL    |       |
| dname   | varchar(20) | YES  |     | NULL    |       |
| loc     | varchar(40) | YES  |     | NULL    |       |
| descri  | varchar(20) | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+

4.3刪除字段

MariaDB [company]> ALTER TABLE tab_dept DROP descri3;
Query OK, 0 rows affected (0.05 sec)               
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [company]> DESC tab_dept;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| descri2 | varchar(20) | YES  |     | NULL    |       |
| depton  | int(11)     | YES  |     | NULL    |       |
| dname   | varchar(20) | YES  |     | NULL    |       |
| loc     | varchar(40) | YES  |     | NULL    |       |
| descri  | varchar(20) | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+

4.4修改字段

------------1、修改字段的數據類型（把descri的字段類型修改爲int）------------
MariaDB [company]> ALTER TABLE tab_dept MODIFY descri INT;
Query OK, 0 rows affected (0.04 sec)               
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [company]> DESC tab_dept;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| descri2 | varchar(20) | YES  |     | NULL    |       |
| depton  | int(11)     | YES  |     | NULL    |       |
| dname   | varchar(20) | YES  |     | NULL    |       |
| loc     | varchar(40) | YES  |     | NULL    |       |
| descri  | int(11)     | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+

------------2、修改字段的名字（change 就屬性名 新屬性名 舊數據類型）------------
MariaDB [company]> ALTER TABLE tab_dept CHANGE loc location VARCHAR(40);
Query OK, 0 rows affected (0.03 sec)               
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [company]> DESC tab_dept;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| descri2  | varchar(20) | YES  |     | NULL    |       |
| depton   | int(11)     | YES  |     | NULL    |       |
| dname    | varchar(20) | YES  |     | NULL    |       |
| location | varchar(40) | YES  |     | NULL    |       |
| descri   | int(11)     | YES  |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+

------------3、同時修改字段的名字和屬性------------
MariaDB [company]> ALTER TABLE tab_dept CHANGE descri2 Age INT;
Query OK, 0 rows affected (0.05 sec)               
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [company]> DESC tab_dept;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| Age      | int(11)     | YES  |     | NULL    |       |
| depton   | int(11)     | YES  |     | NULL    |       |
| dname    | varchar(20) | YES  |     | NULL    |       |
| location | varchar(40) | YES  |     | NULL    |       |
| descri   | int(11)     | YES  |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+

------------4、修改字段的順序------------
MariaDB [company]> ALTER TABLE tab_dept MODIFY location VARCHAR(40) FIRST;
Query OK, 0 rows affected (0.04 sec)               
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [company]> DESC tab_dept;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| location | varchar(40) | YES  |     | NULL    |       |
| Age      | int(11)     | YES  |     | NULL    |       |
| depton   | int(11)     | YES  |     | NULL    |       |
| dname    | varchar(20) | YES  |     | NULL    |       |
| descri   | int(11)     | YES  |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+