查看已有的數據庫：
mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | test | +--------------------+ 2 rows in set (0.05 sec)
新建數據庫語句:
mysql> create database wzu; Query OK, 1 row affected (0.05 sec) mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | test | | wzu | +--------------------+ 3 rows in set (0.05 sec)
要對某個數據庫進行操作時首先要選中這個數據庫,使用use <dbname>：
mysql> use wzu
Database changed
創建表格:
命令:create table ＜表名＞ ( ＜屬性名 屬性類型 ［修飾］＞ );
create table student(sno char(9) primary key,sname char(20) unique,ssex char(2),sage smallint, sdept char(20)); create table course(cno char(4) primary key,cname char(40) not null,cpno char(4),ccredit smallint,foreign key(cpno) references course(cno)); create table sc(sno char(9),cno char(4),grade smallint,primary key(sno,cno),foreign key(sno) references student(sno),foreign key(cno) references course(cno));
刪除表格:
命令：drop table ＜表名＞;
mysql> drop table emp;
Query OK, 0 rows affected (0.41 sec)
查看數據庫中有哪些表格:
mysql> show tables;
+---------------+
| Tables_in_wzu |
+---------------+
| course |
| sc |
| student |
+---------------+
更改外鍵約束:
1 set foreign_key_checks=0; //忽略外鍵檢查 2 set foreign_key_checks=1; //重啟外鍵檢查
更改表中某屬性的數據類型:
命令:alter table ＜表名＞ modify ＜需要更改的屬性＞ ＜想要更改的類型＞；
如:student 表中的sno字段改成varchar(11)
mysql> alter table student modify sno varchar(11); Query OK, 0 rows affected (0.15 sec) Records: 0 Duplicates: 0 Warnings: 0
可以用desc ＜表名＞ 來查看表格結構：
mysql> desc student; +-------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+-------+ | sno | varchar(11) | NO | PRI | | | | sname | varchar(20) | YES | UNI | NULL | | | ssex | varchar(2) | YES | | NULL | | | sage | smallint(6) | YES | | NULL | | | sdept | varchar(20) | YES | | NULL | | +-------+-------------+------+-----+---------+-------+
表格插入數據:
命令：insert into <表名> values( 填,入,相,應,的,值 );
1 insert into student values('1024','測試','男','18','CS');
刪除一行數據:
命令:delete from <表名> where [條件];
1 mysql> delete from emp where empno='232';
修改一行數據：
命令：update <表名> set [屬性名]=[值] [where] [條件]
1 mysql> update course set cpno=null where cpno='NULL';
表格中的簡單數據查詢:
select * from [表名]
如:select * from student;
* 表示查詢表格中所有的列,也可以用列名加','隔開來選擇自己需要的數據
mysql> select * from student; +-------------+--------+------+------+-------+ | sno | sname | ssex | sage | sdept | +-------------+--------+------+------+-------+ | 1024 | 測試 | 男 | 18 | CS | | 1621116 | 周帥 | 男 | 21 | CS | +-------------+--------+------+------+-------+ mysql> select sno,sname from student; +-------------+--------+ | sno | sname | +-------------+--------+ | 1024 | 測試 | | 1621116 | 周帥 | +-------------+--------+
給已創建的表格增加一欄屬性:
alter table <表名> add <屬性名> <屬性域>;
如:
mysql> alter table dept add type varchar(11); Query OK, 4 rows affected (0.62 sec) Records: 4 Duplicates: 0 Warnings: 0 mysql> desc dept; +--------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------+--------------+------+-----+---------+-------+ | deptno | decimal(2,0) | NO | PRI | NULL | | | dname | varchar(14) | NO | | NULL | | | loc | varchar(13) | YES | | NULL | | | type | varchar(11) | YES | | NULL | | +--------+--------------+------+-----+---------+-------+
在已創建的表格中刪除一欄屬性:
alter table <表名> drop <屬性名>;
如:
mysql> alter table dept drop type; Query OK, 4 rows affected (0.57 sec) Records: 4 Duplicates: 0 Warnings: 0 mysql> desc dept; +--------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------+--------------+------+-----+---------+-------+ | deptno | decimal(2,0) | NO | PRI | NULL | | | dname | varchar(14) | NO | | NULL | | | loc | varchar(13) | YES | | NULL | | +--------+--------------+------+-----+---------+-------+
當發現一個操作有warning時 可以通過show warnings；來查看警告信息：
mysql> show warnings; +---------+------+-----------------------------------------------------------------------------------+ | Level | Code | Message | +---------+------+-----------------------------------------------------------------------------------+ | Warning | 1366 | Incorrect string value: '\xE6\x9D\x8E\xE5\x8B\x87' for column 'sname' at row 1 | | Warning | 1366 | Incorrect string value: '\xE7\x94\xB7' for column 'ssex' at row 1 | | Warning | 1366 | Incorrect string value: '\xE6\x95\xB0\xE6\x8D\xAE...' for column 'cname' at row 1 | +---------+------+-----------------------------------------------------------------------------------+
此處的問題主要是因為插入的編碼格式不兼容（插入的數據編碼為utf8 表格的編碼為latinl）
解決方法見mysql/mariadb學習過程中出現的問題與解決
mysql查看當前選擇的數據庫:
mysql> select database(); +------------+ | database() | +------------+ | groupdb | +------------+
//或者：
mysql> show tables;
+-------------------+
| Tables_in_groupdb |//此處為當前數據庫
+-------------------+
| course |
| dept |
| emp |
| jwc |
| salgrade |
| sc |
| student |
| temp |
+-------------------+
//或者：
mysql> status;
--------------
mysql Ver 14.14 Distrib 5.7.14, for Win64 (x86_64)
Connection id: 2721
Current database: groupdb //此處為當前數據庫
Current user: group@122.228.131.86
SSL: Not in use
Using delimiter: ;
Server version: 5.5.56-MariaDB MariaDB Server
Protocol version: 10
Connection: AAA.AAA.AAA.AAA via TCP/IP
Server characterset: utf8
Db characterset: utf8
Client characterset: utf8
Conn. characterset: utf8
TCP port: 3306
Uptime: 2 days 5 hours 25 min 51 sec
Threads: 2 Questions: 549 Slow queries: 0 Opens: 26 Flush tables: 2 Open tables: 44 Queries per second avg: 0.002
2018-04-30
判斷一個值是否為NULL：
使用 is 關鍵字而不能用 = 來判斷
mysql> select * from course where cpno is null; +-----+--------------+------+---------+ | cno | cname | cpno | ccredit | +-----+--------------+------+---------+ | 2 | 高等數學 | NULL | 2 | | 6 | 數據處理 | NULL | 2 | +-----+--------------+------+---------+ 2 rows in set (0.05 sec) mysql> select * from course where cpno is not null; +-----+--------------+------+---------+ | cno | cname | cpno | ccredit | +-----+--------------+------+---------+ | 1 | 數據庫 | 5 | 4 | | 3 | 信息系統 | 1 | 4 | | 4 | 操作系統 | 6 | 3 | | 5 | 數據結構 | 7 | 4 | | 7 | C語言 | 6 | 4 | +-----+--------------+------+---------+