标签：
目录
1、SQL语句分类
2、DDL语句
3、DML语句
4、DCL语句
5、事务相关语句
6、mysql查询
6.1、单表简单查询
6.2、多表组合查询
6.2.1、联结查询（交叉联结，内联结，外联结（左外联结、右外联结））
6.2.2、联合查询（UNION）
6.2.3、内联结
6.3、子查询
6.3.1、WHERE子查询
6.3.2、FROM子查询
1、SQL语句分类
DDL：数据定义语言，用来定义数据库对象，包括数据库、表、索引、存储过程、存储函数、约束、触发器、事件调度器等
DML：数据操作语言，包括CRUD（Insert，Select，Replace，Update，Delete）
DCL：数据控制语言，包括grant，revoke
与事务相关的语言：start transaction，commit，rollback，save point
2、DDL语句
2.1、数据库操作
a)、创建数据库：
语法：mysql> create {database | schema} [if not exists] 数据库名; #“if not exists”是用来作条件判断
举例：
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mysql> create database if not exists mydb; #创建一个mydb数据库Query OK, 1 row affected (0.00 sec)mysql> show databases;+--------------------+| Database |+--------------------+| information_schema || mydb || mysql || performance_schema || test |+--------------------+5 rows in set (0.00 sec)mysql> create schema if not exists mydb; #尝试再次建立mydb数据库Query OK, 1 row affected, 1 warning (0.00 sec)mysql> show warnings; #查看警告信息+-------+------+-----------------------------------------------+| Level | Code | Message |+-------+------+-----------------------------------------------+| Note | 1007 | Can ‘t create database ‘ mydb‘; database exists |+-------+------+-----------------------------------------------+1 row in set (0.00 sec) |
b)、删除数据库：
语法：
mysql> drop {database | schema} [if exists] 数据库名;
举例：
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mysql> show databases;+--------------------+| Database |+--------------------+| information_schema || mydb || mysql || performance_schema || test |+--------------------+5 rows in set (0.00 sec)mysql> drop schema if exists mydb;Query OK, 0 rows affected (0.00 sec)mysql> show databases;+--------------------+| Database |+--------------------+| information_schema || mysql || performance_schema || test |+--------------------+4 rows in set (0.00 sec) |
c)、修改数据库
语法：
mysql> alter {database | schema} 数据库名 [DEFAULT] CHARACTER SET [=] charset_name ｜[DEFAULT] COLLATE [=] collation_name
mysql> alter {database | schema} 数据库名 upgrade data directory name; #此语句用在数据进行升级后用来升级数据字典
2.2、数据表操作
a)、创建字段自定义表
语法：
mysql> create table [if not exists] 表名 (字段1 字段定义,字段2 字段定义, ...) 众多选项
mysql> help create table; #获取表创建的帮助。
举例：
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mysql> use test ;mysql> create table if not exists tb1 ( id int unsigned auto_increment primary key,name char(30) not null,age tinyint unsigned,class char(20) not null ) character set = utf8 engine = innodb; |
以下三个sql语句都可查数据库中的表状态：
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mysql> show table status from test \Gmysql> show table status in test \Gmysql> show table status like ‘tb1‘ ; |
b)、以select语句查询到的数据为结果来创建一张表
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mysql> use mydb1;mysql> create table if not exists tb2 select user,host,password from mysql.user;Query OK, 3 rows affected (0.02 sec)Records: 3 Duplicates: 0 Warnings: 0mysql> select * from tb2;+------+------------+-------------------------------------------+| user | host | password |+------+------------+-------------------------------------------+| root | localhost | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 || root | db\_server | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 || root | 127.0.0.1 | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |+------+------------+-------------------------------------------+3 rows in set (0.00 sec)注：这种方式创建出来的表，表的表结构与源表的表结构是不同的，也就是说字段中的定义和修饰符不会全部在新表中都有 |
c)、模仿一张表的表结构来创建一张只有表结构的表
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mysql> create table if not exists tb3 like tb2;Query OK, 0 rows affected (0.03 sec)mysql> desc tb3;+----------+----------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+----------+----------+------+-----+---------+-------+| user | char(16) | NO | | | || host | char(60) | NO | | | || password | char(41) | NO | | | |+----------+----------+------+-----+---------+-------+3 rows in set (0.03 sec)mysql> desc tb2;+----------+----------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+----------+----------+------+-----+---------+-------+| user | char(16) | NO | | | || host | char(60) | NO | | | || password | char(41) | NO | | | |+----------+----------+------+-----+---------+-------+3 rows in set (0.00 sec)mysql> select * from tb3; #tb3中是没有数据的Empty set (0.02 sec) |
开动脑筋：
怎样从一个表中挑选一些数据生成一张新表，且新表的表结构(字段定义、修饰符等)与源表是完成相同的。
实现方式分两部来完成，先创建和源表一样表结构的表，再以select的方式插入数据到此表。
实现：
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mysql> DESC tb1;+-------+---------------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |+-------+---------------------+------+-----+---------+----------------+| id | int(10) unsigned | NO | PRI | NULL | auto_increment || name | char(20) | NO | | NULL | || age | tinyint(3) unsigned | NO | | NULL | |+-------+---------------------+------+-----+---------+----------------+3 rows in set (0.00 sec)mysql> SELECT * FROM tb1;+----+-------+-----+| id | name | age |+----+-------+-----+| 1 | jack | 29 || 2 | jason | 39 || 3 | tom | 37 || 4 | luck | 22 || 7 | root | 0 || 8 | root | 0 || 9 | root | 0 |+----+-------+-----+7 rows in set (0.01 sec)mysql> CREATE TABLE IF NOT EXISTS tb2 LIKE tb1; #创建tb2以tb1的表结构为源Query OK, 0 rows affected, 1 warning (0.01 sec)mysql> DESC tb2; #tb2的表结构和tb1的表结构是完成相同的+-------+---------------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |+-------+---------------------+------+-----+---------+----------------+| id | int(10) unsigned | NO | PRI | NULL | auto_increment || name | char(20) | NO | | NULL | || age | tinyint(3) unsigned | NO | | NULL | |+-------+---------------------+------+-----+---------+----------------+3 rows in set (0.00 sec)mysql> INSERT INTO tb2 SELECT * FROM tb1 WHERE age>30; #只把tb1中年龄大于30的数据插入到新表中Query OK, 2 rows affected (0.02 sec)Records: 2 Duplicates: 0 Warnings: 0mysql> SELECT * FROM tb2; #验证数据+----+-------+-----+| id | name | age |+----+-------+-----+| 2 | jason | 39 || 3 | tom | 37 |+----+-------+-----+2 rows in set (0.00 sec)这样就可实现保持源表的表结构提取所需数据。 |
d)、删除表
mysql> drop table [if exists] 表名;
e)、修改表名称、字段、定义、修饰符等
用help alter table来获取帮助
新增字段，删除字段
modify 修改指定字段定义：
change 修改字段名
rename 新表名
举例：
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mysql> SELECT * FROM tb2;+------+------+| id | name |+------+------+| 1 | Zcj || 2 | Tom |+------+------+2 rows in set (0.00 sec)mysql> DESC tb2;+-------+----------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+-------+----------+------+-----+---------+-------+| id | int(11) | YES | | NULL | || name | char(30) | YES | | NULL | |+-------+----------+------+-----+---------+-------+mysql> ALTER TABLE tb2 ADD Age TINYINT UNSIGNED AFTER id ; #增加“Age”字段Query OK, 2 rows affected (0.04 sec)Records: 2 Duplicates: 0 Warnings: 0mysql> SELECT * FROM tb2;+------+------+------+| id | Age | name |+------+------+------+| 1 | NULL | Zcj || 2 | NULL | Tom |+------+------+------+mysql> ALTER TABLE tb2 DROP Age; #删除字段“Age”Query OK, 2 rows affected (0.06 sec)Records: 2 Duplicates: 0 Warnings: 0mysql> SELECT * FROM tb2;+------+------+| id | name |+------+------+| 1 | Zcj || 2 | Tom |+------+------+mysql> ALTER TABLE tb2 MODIFY id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY; #修改id字段的定义Query OK, 2 rows affected (0.01 sec)Records: 2 Duplicates: 0 Warnings: 0mysql> DESC tb2;+-------+------------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |+-------+------------------+------+-----+---------+----------------+| id | int(10) unsigned | NO | PRI | NULL | auto_increment || name | char(30) | YES | | NULL | |+-------+------------------+------+-----+---------+----------------+mysql> ALTER TABLE tb2 CHANGE name fullname CHAR(50) NOT NULL; #修改字段name的名称及定义Query OK, 2 rows affected (0.01 sec)Records: 2 Duplicates: 0 Warnings: 0mysql> DESC tb2;+----------+------------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |+----------+------------------+------+-----+---------+----------------+| id | int(10) unsigned | NO | PRI | NULL | auto_increment || fullname | char(50) | NO | | NULL | |+----------+------------------+------+-----+---------+----------------+mysql> ALTER TABLE tb2 RENAME newtb2; #修改表名Query OK, 0 rows affected (0.00 sec)mysql> DESC newtb2;+----------+------------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |+----------+------------------+------+-----+---------+----------------+| id | int(10) unsigned | NO | PRI | NULL | auto_increment || fullname | char(50) | NO | | NULL | |+----------+------------------+------+-----+---------+----------------+ |
3、DML语句
3.1、insert：用来插入数据
语法：
mysql> insert into 表名 [(字段名，...)] {values | value} (值,...)
mysql> insert into 表名 set 字段名=值，...
举例：
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mysql> CREATE TABLE IF NOT EXISTS tb1 ( id int unsigned auto_increment primary key,name char(20) not null,age tinyint unsigned not null); #先创建一张表 |
a)、插入多行数据
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mysql> INSERT INTO tb1 (name,age) VALUES ( ‘jack‘ ,29),( ‘jason‘ ,39),( ‘tom‘ ,37); |
b)、插入一行数据
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mysql> INSERT INTO tb1 SET name= ‘luck‘ ,age=22;mysql> SELECT * FROM tb1; #查看表数据+----+-------+-----+| id | name | age |+----+-------+-----+| 1 | jack | 29 || 2 | jason | 39 || 3 | tom | 37 || 4 | luck | 22 |+----+-------+-----+4 rows in set (0.00 sec) |
c)、以select结果插入数据
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mysql> INSERT INTO tb1 (name) SELECT user FROM mysql.user; #把user表中的用户信息检索出来填充到tb1表中的name字段Query OK, 3 rows affected, 1 warning (0.08 sec)Records: 3 Duplicates: 0 Warnings: 1mysql> SHOW WARNINGS; #有个警告信息，因为创建表时age字段是not null的,只填充了name字段，没有age字段的相应数据+---------+------+------------------------------------------+| Level | Code | Message |+---------+------+------------------------------------------+| Warning | 1364 | Field ‘age‘ doesn‘t have a default value |+---------+------+------------------------------------------+1 row in set (0.00 sec)mysql> SELECT * FROM tb1; #自动把age字段填充为0+----+-------+-----+| id | name | age |+----+-------+-----+| 1 | jack | 29 || 2 | jason | 39 || 3 | tom | 37 || 4 | luck | 22 || 7 | root | 0 || 8 | root | 0 || 9 | root | 0 |+----+-------+-----+7 rows in set (0.08 sec) |
3.2、replace：用来替换表的数据，如果源表中没有此数据则增加数据
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mysql> DESC tb2; #name字段是唯一键索引+-------+---------------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |+-------+---------------------+------+-----+---------+----------------+| id | int(10) unsigned | NO | PRI | NULL | auto_increment || name | char(20) | NO | UNI | NULL | || age | tinyint(3) unsigned | NO | | NULL | |+-------+---------------------+------+-----+---------+----------------+3 rows in set (0.00 sec)mysql> SELECT * FROM tb2;+----+-------+-----+| id | name | age |+----+-------+-----+| 1 | jack | 29 || 2 | jason | 39 || 3 | tom | 37 || 4 | luck | 22 |+----+-------+-----+4 rows in set (0.00 sec)mysql> REPLACE INTO tb2 SET name= ‘jack‘ ,age=33; #因原表中有jack这个用户，replace这个命令会先删除原来的那一行，再新增加一行，所以会有两行受到影响Query OK, 2 rows affected (0.04 sec)mysql> REPLACE INTO tb2 SET name= ‘zhaochj‘ ,age=29; #因原表中没有zhaochj这个用户，所以直接在最后增加Query OK, 1 row affected (0.03 sec)mysql> SELECT * FROM tb2;+----+---------+-----+| id | name | age |+----+---------+-----+| 2 | jason | 39 || 3 | tom | 37 || 4 | luck | 22 || 5 | jack | 33 || 6 | zhaochj | 29 |+----+---------+-----+5 rows in set (0.02 sec) |
3.3、update：修改表中的数据
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mysql> SELECT * FROM tb2;+----+---------+-----+| id | name | age |+----+---------+-----+| 2 | jason | 39 || 3 | tom | 37 || 4 | luck | 22 || 5 | jack | 33 || 6 | zhaochj | 29 |+----+---------+-----+5 rows in set (0.02 sec)mysql> UPDATE tb2 SET age=33 WHERE name= ‘zhaochj‘ ;Query OK, 1 row affected (0.01 sec)Rows matched: 1 Changed: 1 Warnings: 0mysql> UPDATE tb2 SET age=11 LIMIT 2; #修改前两行的年龄为11Query OK, 2 rows affected (0.01 sec)Rows matched: 2 Changed: 2 Warnings: 0mysql> SELECT * FROM tb2;+----+---------+-----+| id | name | age |+----+---------+-----+| 2 | jason | 11 || 3 | tom | 11 || 4 | luck | 22 || 5 | jack | 33 || 6 | zhaochj | 33 |+----+---------+-----+5 rows in set (0.02 sec) |
3.4、delete 删除表中数据
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mysql> SELECT * FROM tb2;+----+---------+-----+| id | name | age |+----+---------+-----+| 2 | jason | 11 || 3 | tom | 11 || 4 | luck | 22 || 5 | jack | 33 || 6 | zhaochj | 33 |+----+---------+-----+5 rows in set (0.02 sec)mysql>mysql> DELETE FROM tb2 WHERE name= ‘zhaochj‘ ; #加上where子句限定删除的范围Query OK, 1 row affected (0.38 sec)mysql> SELECT * FROM tb2;+----+-------+-----+| id | name | age |+----+-------+-----+| 2 | jason | 11 || 3 | tom | 11 || 4 | luck | 22 || 5 | jack | 33 |+----+-------+-----+4 rows in set (0.00 sec)mysql> DELETE FROM tb2; #这样直接把表中的数据全部删除Query OK, 4 rows affected (0.01 sec)mysql> SELECT * FROM tb2;Empty set (0.00 sec)mysql> INSERT INTO tb2 (name,age) VALUES ( ‘zcj‘ ,29); #试着插入一行数据Query OK, 1 row affected (0.01 sec)mysql> SELECT * FROM tb2; #查看数据发现id号不是从"1"开始的，这是因为字段“id”被定义成了“auto_increment”了+----+------+-----+| id | name | age |+----+------+-----+| 7 | zcj | 29 |+----+------+-----+1 row in set (0.03 sec)mysql> TRUNCATE TABLE tb2; #清空一张表，应该用这个命令，表示重置表，会清空“auto_increment”的计数器Query OK, 0 rows affected (0.05 sec)mysql> INSERT INTO tb2 (name,age) VALUES ( ‘zcj‘ ,29);Query OK, 1 row affected (0.03 sec)mysql> SELECT * FROM tb2; #id号又从“1”开始+----+------+-----+| id | name | age |+----+------+-----+| 1 | zcj | 29 |+----+------+-----+1 row in set (0.00 sec) |
4、DCL语句
4.1、权限赋予
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mysql> GRANT select ON mydb2.tb1 TO ‘mydb2user1‘ @ ‘%‘ IDENTIFIED BY ‘111111‘ ;#对mydb2数据库中的tb1表授予mydb2user1用户可在任意主机以6个1为密码登陆，但权限只有selectmysql> SHOW GRANTS FOR mydb2user1; #显示mydb2user1用户的权限信息+-----------------------------------------------------------------------------------------------------------+| Grants for mydb2user1@% |+-----------------------------------------------------------------------------------------------------------+| GRANT USAGE ON *.* TO ‘mydb2user1‘ @ ‘%‘ IDENTIFIED BY PASSWORD ‘*FD571203974BA9AFE270FE62151AE967ECA5E0AA‘ || GRANT SELECT ON `mydb2`.`tb1` TO ‘mydb2user1‘ @ ‘%‘ |+-----------------------------------------------------------------------------------------------------------+2 rows in set (0.00 sec)验证权限是否生效：[root@mariadb ~] # mysql -umydb2user1 -p111111 #以mydb2user1登陆mysql> SHOW DATABASES;+--------------------+| Database |+--------------------+| information_schema || mydb2 || test |+--------------------+mysql> USE mydb2;Database changedmysql> SHOW TABLES;+-----------------+| Tables_in_mydb2 |+-----------------+| tb1 |+-----------------+mysql> SELECT * FROM tb1;+------+------+| id | name |+------+------+| 1 | Zcj || 2 | Tom || 3 | Jack |+------+------+mysql> INSERT INTO tb1 ( id ,name) VALUES (4, ‘Cora‘ ); #没有权限插入数据ERROR 1142 (42000): INSERT command denied to user ‘mydb2user1‘ @ ‘localhost‘ for table ‘tb1‘mysql> GRANT insert ON mydb2.tb1 TO ‘mydb2user1‘ @ ‘%‘ ; #再赋予insert权限Query OK, 0 rows affected (0.00 sec)mysql> SHOW GRANTS FOR mydb2user1;+-----------------------------------------------------------------------------------------------------------+| Grants for mydb2user1@% |+-----------------------------------------------------------------------------------------------------------+| GRANT USAGE ON *.* TO ‘mydb2user1‘ @ ‘%‘ IDENTIFIED BY PASSWORD ‘*FD571203974BA9AFE270FE62151AE967ECA5E0AA‘ || GRANT SELECT, INSERT ON `mydb2`.`tb1` TO ‘mydb2user1‘ @ ‘%‘ |+-----------------------------------------------------------------------------------------------------------+2 rows in set (0.00 sec)[root@mariadb ~] # mysql -umydb2user1 -p111111 #再以mydb2user1登陆mysql> INSERT INTO tb1 ( id ,name) VALUES (4, ‘Cora‘ );Query OK, 1 row affected (0.07 sec)mysql> SELECT * FROM tb1; #数据已插入+------+------+| id | name |+------+------+| 1 | Zcj || 2 | Tom || 3 | Jack || 4 | Cora |+------+------+4 rows in set (0.00 sec) |
4.2、回收权限
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[root@mariadb ~] # mysql -uroot -p123456 #以root登陆mysql> REVOKE insert ON mydb2.tb1 FROM mydb2user1;Query OK, 0 rows affected (0.00 sec)[root@mariadb ~] # mysql -umydb2user1 -p111111 #以mydb2user1登陆mysql> INSERT INTO mydb2.tb1 ( id ,name) VALUES (5, ‘Lucky‘ ); #无法插入数据，insert权限已被回收ERROR 1142 (42000): INSERT command denied to user ‘mydb2user1‘ @ ‘localhost‘ for table ‘tb1‘ |
5、事务相关语句
mysql> START TRANSACTION; #开始事务
mysql> SAVEPOINT point_name; #保存一个事务的位置,以方便撤销事务
mysql> ROLLBACK TO point_name; #回滚到一个点
mysql> ROLLBACK; #回滚到开始事务时的状态
mysql> COMMIT; #提交事务
举例：
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mysql> START TRANSACTION; #开始事务Query OK, 0 rows affected (0.02 sec)mysql> SELECT * FROM tb1;+------+------+| id | name |+------+------+| 1 | Zcj || 2 | Tom || 3 | Jack || 4 | Cora |+------+------+4 rows in set (0.00 sec)mysql> INSERT INTO tb1 ( id ,name) VALUES (5, ‘Lucky‘ ); #插入一行数据Query OK, 1 row affected (0.00 sec)mysql> SELECT * FROM tb1;+------+-------+| id | name |+------+-------+| 1 | Zcj || 2 | Tom || 3 | Jack || 4 | Cora || 5 | Lucky |+------+-------+5 rows in set (0.00 sec)mysql> SAVEPOINT p1; #在有id为5这行数据时创建一个保存点Query OK, 0 rows affected (0.01 sec)mysql> DELETE FROM tb1 WHERE id = 2; #删除一行数据Query OK, 1 row affected (0.00 sec)mysql> SELECT * FROM tb1;+------+-------+| id | name |+------+-------+| 1 | Zcj || 3 | Jack || 4 | Cora || 5 | Lucky |+------+-------+4 rows in set (0.00 sec)mysql> ROLLBACK TO p1; #回滚到保存点p1的状态Query OK, 0 rows affected (0.00 sec)mysql> SELECT * FROM tb1;+------+-------+| id | name |+------+-------+| 1 | Zcj || 2 | Tom || 3 | Jack || 4 | Cora || 5 | Lucky |+------+-------+5 rows in set (0.00 sec)mysql> ROLLBACK; #回滚到事务开始时的状态Query OK, 0 rows affected (0.00 sec)mysql> SELECT * FROM tb1;+------+------+| id | name |+------+------+| 1 | Zcj || 2 | Tom || 3 | Jack || 4 | Cora |+------+------+4 rows in set (0.00 sec)mysql> COMMIT; #提交事务Query OK, 0 rows affected (0.00 sec) |
6、mysql查询
为演示各种SELECT语句，建立以下几个表：
一)、表名为“students_tb”，字段为：StudentID，Name，Age，Gender，ClassID，分别存放学生的名字、年龄、性别、有班级的ID号，具体的班级存放在另一张表中
二)、表名为“classes_tb”，字段为：ClassID，Class，TeacherID，分别存放班级的ID号，具体的班级名，这个班级是哪个老师负责的ID号，具体的负责的老师存放在另一张表中
三)、表名为“teacher_tb”，字段为：TeacheID，Name，Age，Gender，分别存放老师的ID号，老师的名字，年龄，性别
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mysql> USE mydb1;mysql> CREATE TABLE IF NOT EXISTS students_tb (StudentID SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,Name CHAR(30) NOT NULL,Age TINYINT UNSIGNED,Gender ENUM( ‘M‘ , ‘F‘ ),ClassID TINYINT UNSIGNED NOT NULL);mysql> INSERT INTO students_tb (Name,Age,Gender,ClassID) VALUES ( ‘Tom‘ ,17, ‘M‘ ,1),( ‘Jack‘ ,18, ‘M‘ ,3),( ‘Lucy‘ ,21, ‘F‘,6),( ‘Jimima‘ ,15, ‘F‘ ,4),( ‘Jimmy‘ ,30, ‘M‘ ,9),( ‘Jim‘ ,26, ‘M‘ ,7);mysql> SELECT * FROM students_tb;+-----------+--------+------+--------+---------+| StudentID | Name | Age | Gender | ClassID |+-----------+--------+------+--------+---------+| 1 | Tom | 17 | M | 1 || 2 | Jack | 18 | M | 3 || 3 | Lucy | 21 | F | 6 || 4 | Jimima | 15 | F | 4 || 5 | Jimmy | 30 | M | 9 || 6 | Jim | 26 | M | 7 |+-----------+--------+------+--------+---------+mysql> CREATE TABLE IF NOT EXISTS classes_tb (ClassID TINYINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,Class CHAR(20) NOT NULL,TeacherID TINYINT UNSIGNED NOT NULL);mysql> ALTER TABLE classes_tb ADD UNIQUE KEY (Class); #这个表中的班别应该是唯一的，所以用此sql语句来修改Query OK, 0 rows affected (0.08 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> DESC classes_tb;+-----------+---------------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |+-----------+---------------------+------+-----+---------+----------------+| ClassID | tinyint(3) unsigned | NO | PRI | NULL | auto_increment || Class | char(20) | NO | UNI | NULL | || TeacherID | tinyint(3) unsigned | NO | | NULL | |+-----------+---------------------+------+-----+---------+----------------+3 rows in set (0.00 sec)mysql> INSERT INTO classes_tb (Class,TeacherID) VALUES ( ‘class1‘ ,5),( ‘class2‘ ,2),( ‘class3‘ ,5),( ‘class4‘ ,2),( ‘class5‘ ,4),( ‘class6‘ ,1);mysql> SELECT * FROM classes_tb;+---------+--------+-----------+| ClassID | Class | TeacherID |+---------+--------+-----------+| 1 | class1 | 5 || 2 | class2 | 2 || 3 | class3 | 5 || 4 | class4 | 2 || 5 | class5 | 4 || 6 | class6 | 1 |+---------+--------+-----------+mysql> CREATE TABLE IF NOT EXISTS teacher_tb (TeacherID TINYINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,Name CHAR(30) NOT NULL,Age TINYINT UNSIGNED,Gender ENUM( ‘M‘ , ‘F‘ ));mysql> INSERT INTO teacher_tb (Name,Age,Gender) VALUES ( ‘Wang baoqiang‘ ,30, ‘M‘ ),( ‘Zhang shanfeng‘ ,32, ‘F‘ ),( ‘Zhao qiang‘ ,40, ‘M‘ ),( ‘Ying hui‘ ,50, ‘M‘ ),( ‘Feng bing‘ ,46, ‘M‘ ),( ‘Qian qiang‘ ,37, ‘M‘ ),( ‘Shun bin‘ ,68, ‘M‘ );mysql> SELECT * FROM teacher_tb;+-----------+----------------+------+--------+| TeacherID | Name | Age | Gender |+-----------+----------------+------+--------+| 1 | Wang baoqiang | 30 | M || 2 | Zhang shanfeng | 32 | F || 3 | Zhao qiang | 40 | M || 4 | Ying hui | 50 | M || 5 | Feng bing | 46 | M || 6 | Qian qiang | 37 | M || 7 | Shun bin | 68 | M |+-----------+----------------+------+--------+三个表创建及数据插入完成。 |
6.1、单表简单查询
语法：
SELECT 字段，字段，... FROM 表名 WHERE 子句;
举例：
查询students_tb表中前5个学生的姓名和年龄
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mysql> SELECT Name,Age FROM students_tb LIMIT 5;+--------+------+| Name | Age |+--------+------+| Tom | 17 || Jack | 18 || Lucy | 21 || Jimima | 15 || Jimmy | 30 |+--------+------+ |
a)、比较运算：>,<,>=,<=,!=,<>,<=>
在students_tb表中查询年龄大于20的学生有哪些：
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mysql> SELECT Name,Age FROM students_tb WHERE Age>20;+-------+------+| Name | Age |+-------+------+| Lucy | 21 || Jimmy | 30 || Jim | 26 |+-------+------+ |
在students_tb表中查询年龄不等于30的学生有哪些：
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mysql> SELECT Name,Age FROM students_tb WHERE Age!=30;+--------+------+| Name | Age |+--------+------+| Tom | 17 || Jack | 18 || Lucy | 21 || Jimima | 15 || Jim | 26 |+--------+------+ |
在students_tb表中查询年龄不等于30和不等于15的学生有哪些：
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mysql> SELECT Name,Age FROM students_tb WHERE Age!=30 and Age!=15;+------+------+| Name | Age |+------+------+| Tom | 17 || Jack | 18 || Lucy | 21 || Jim | 26 |+------+------+ |
b)、BETWEEN...AND..表示在一个范围内的数据
在students_tb表中查询年龄在20到30之间的学生：
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mysql> SELECT Name,Age FROM students_tb WHERE Age BETWEEN 20 AND 30;+-------+------+| Name | Age |+-------+------+| Lucy | 21 || Jimmy | 30 || Jim | 26 |+-------+------+ |
c)、IN (元素，...)，表示在一个范围内匹配
在students_tb表中查询年龄是18或26或30的学生：
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mysql> SELECT Name,Age FROM students_tb WHERE Age IN (18,26,30); #表示查询一个集合内的数据+-------+------+| Name | Age |+-------+------+| Jack | 18 || Jimmy | 30 || Jim | 26 |+-------+------+ |
d)、LIKE子句与RLIKE子句
在students_tb表中查询姓名中有字母“J”，且在后边跟了任意个字符的用户：
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mysql> SELECT Name,Age FROM students_tb WHERE Name LIKE ‘J%‘ ; +--------+------+| Name | Age |+--------+------+| Jack | 18 || Jimima | 15 || Jimmy | 30 || Jim | 26 |+--------+------+#通配符匹配有“%”，“_” ，“%”表示匹配任意个任意字符，“_”表示匹配任意单个字符 |
在students_tb表中查询姓名以“J”开头，后接任意字符,再接有一个m或多个m，再后接任意个字符，并且以y结尾的学生：
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mysql> SELECT Name,Age FROM students_tb WHERE Name RLIKE ‘^J.*m+.*y$‘ ; #正则匹配+-------+------+| Name | Age |+-------+------+| Jimmy | 30 |+-------+------+ |
e)、逻辑运算符（NOT,AND,OR）,优先级依次降低
在students_tb表中查询学生姓名以“J”开头，并且年龄大于20的信息：
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mysql> SELECT Name,Age FROM students_tb WHERE Name RLIKE ‘^J‘ && Age>20; #“&&”=“AND”+-------+------+| Name | Age |+-------+------+| Jimmy | 30 || Jim | 26 |+-------+------+ |
在students_tb表中查询年龄是30或者是15的学生：
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mysql> SELECT Name,Age FROM students_tb WHERE Age=30 OR Age=15; #“OR”="||"+--------+------+| Name | Age |+--------+------+| Jimima | 15 || Jimmy | 30 |+--------+------+ |
在students_tb表中查询性别不是“F”的学生：
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mysql> SELECT Name,Gender FROM students_tb WHERE NOT Gender= ‘F‘ ;+-------+--------+| Name | Gender |+-------+--------+| Tom | M || Jack | M || Jimmy | M || Jim | M |+-------+--------+ |
在students_tb表中查询年龄在10到26之间，姓名以“J”或“L”开头的女生：
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mysql> SELECT Name,Age,Gender FROM students_tb WHERE Age>=10 AND Age<=26 AND (Name LIKE ‘J%‘ OR Name LIKE ‘%L‘ ) AND Gender= ‘F‘ ;+--------+------+--------+| Name | Age | Gender |+--------+------+--------+| Jimima | 15 | F |+--------+------+--------+注：逻辑运算是有优先级的，如果不用括号那得到的结果与预想的不一样。 |
f)、聚合函数：MAX(),MIN(),AVG(),SUM(),COUNT()
在students_tb表中查询年龄最大的学生是谁：
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mysql> SELECT Name,Age FROM students_tb WHERE Age = (SELECT MAX(Age) FROM students_tb);+-------+------+| Name | Age |+-------+------+| Jimmy | 30 |+-------+------+ |
在students_tb表中查询年龄最小的学生是谁：
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mysql> SELECT Name,Age FROM students_tb WHERE Age = (SELECT MIN(Age) FROM students_tb);+--------+------+| Name | Age |+--------+------+| Jimima | 15 |+--------+------+ |
在students_tb表中求所有学生年龄的平均值
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mysql> SELECT AVG(Age) FROM students_tb;+----------+| AVG(Age) |+----------+| 21.1667 |+----------+ |
g)、GROUP BY 分组，及HAVING子句
在students_tb表中求男生、女生年龄分别的平均值：
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mysql> SELECT Gender,AVG(Age) FROM students_tb GROUP BY Gender;+--------+----------+| Gender | AVG(Age) |+--------+----------+| M | 22.7500 || F | 18.0000 |+--------+----------+ |
显示students_tb表中分别显示男生，女生的最大年龄：
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mysql> SELECT Gender,MAX(Age) FROM students_tb GROUP BY Gender;+--------+----------+| Gender | MAX(Age) |+--------+----------+| M | 30 || F | 21 |+--------+----------+ |
为了演示HAVING子句，现在加入以下数据：
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mysql> INSERT INTO students_tb (Name,Age,Gender,ClassID) VALUES ( ‘Cora‘ ,25, ‘F‘ ,6),( ‘Echo‘ ,58, ‘F‘ ,7),( ‘张三‘ ,47, ‘M‘,3);mysql> SELECT * FROM students_tb;+-----------+--------+------+--------+---------+| StudentID | Name | Age | Gender | ClassID |+-----------+--------+------+--------+---------+| 1 | Tom | 17 | M | 1 || 2 | Jack | 18 | M | 3 || 3 | Lucy | 21 | F | 6 || 4 | Jimima | 15 | F | 4 || 5 | Jimmy | 30 | M | 9 || 6 | Jim | 26 | M | 7 || 7 | Cora | 25 | F | 6 || 8 | Echo | 58 | F | 7 || 9 | 张三 | 47 | M | 3 |+-----------+--------+------+--------+---------+ |
以班级排序，显示students_tb表中各个班级中年龄最小的同学，只显示年龄小于20的的班级：
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mysql> SELECT ClassID,Name,MIN(Age) FROM students_tb GROUP BY ClassID;+---------+--------+----------+| ClassID | Name | MIN(Age) |+---------+--------+----------+| 1 | Tom | 17 || 3 | Jack | 18 || 4 | Jimima | 15 || 6 | Lucy | 21 || 7 | Jim | 26 || 9 | Jimmy | 30 |+---------+--------+----------+mysql> SELECT ClassID,Name,MIN(Age) FROM students_tb GROUP BY ClassID HAVING MIN(Age)<20;+---------+--------+----------+| ClassID | Name | MIN(Age) |+---------+--------+----------+| 1 | Tom | 17 || 3 | Jack | 18 || 4 | Jimima | 15 |+---------+--------+----------+ |
h)、ORDER BY排序
以性别分组，分别计算男女生的年龄之和，并逆序排列：
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mysql> SELECT Gender,SUM(Age) FROM students_tb GROUP BY Gender ORDER BY SUM(Age) DESC;+--------+----------+| Gender | SUM(Age) |+--------+----------+| M | 138 || F | 119 |+--------+----------+ |
查看students_tb表中男女生各是多少：
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mysql> SELECT Gender,COUNT(Name) FROM students_tb GROUP BY Gender;+--------+-------------+| Gender | COUNT(Name) |+--------+-------------+| M | 5 || F | 4 |+--------+-------------+ |
6.2、多表组合查询
6.2.1、联结查询（交叉联结，内联结，外联结（左外联结、右外联结））
a)、交叉联结（返回笛卡尔集）
关键字：CROSS JOIN
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mysql> SELECT * FROM students_tb CROSS JOIN classes_tb; #结果略，类似数学里的多项式相乘，这种对服务器的开销特别大，极少使用。 |
b)、自然联结：让两张表的某个相同字段进行等值关系联结，是左右外联结的交集
关键字：NATURAL...JOIN
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mysql> SELECT * FROM students_tb NATURAL JOIN classes_tb;+---------+-----------+--------+------+--------+--------+-----------+| ClassID | StudentID | Name | Age | Gender | Class | TeacherID |+---------+-----------+--------+------+--------+--------+-----------+| 1 | 1 | Tom | 17 | M | class1 | 5 || 3 | 2 | Jack | 18 | M | class3 | 5 || 3 | 12 | 张三 | 47 | M | class3 | 5 || 4 | 4 | Jimima | 15 | F | class4 | 2 || 6 | 3 | Lucy | 21 | F | class6 | 1 || 6 | 10 | Cora | 25 | F | class6 | 1 |+---------+-----------+--------+------+--------+--------+-----------+注意：在表students_tb中有些有的ClassID，而在classed_tb中没有相对应的值，采用内联结里是不显示出来的。 |
显示学生的信息，所在的班级也要显示出来：
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mysql> SELECT * FROM students_tb,classes_tb WHERE students_tb.ClassID=classes_tb.ClassID; #其实也是交叉联结过虑后的结果+-----------+--------+------+--------+---------+---------+--------+-----------+| StudentID | Name | Age | Gender | ClassID | ClassID | Class | TeacherID |+-----------+--------+------+--------+---------+---------+--------+-----------+| 1 | Tom | 17 | M | 1 | 1 | class1 | 5 || 2 | Jack | 18 | M | 3 | 3 | class3 | 5 || 9 | 张三 | 47 | M | 3 | 3 | class3 | 5 || 4 | Jimima | 15 | F | 4 | 4 | class4 | 2 || 3 | Lucy | 21 | F | 6 | 6 | class6 | 1 || 7 | Cora | 25 | F | 6 | 6 | class6 | 1 |+-----------+--------+------+--------+---------+---------+--------+-----------+ |
c)、外联结
左外联结（语法：左表 LEFT JOIN 右表 ON 条件）
显示各个同学是哪个班级的，如果此同学还没有给定班级，则留空：
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mysql> SELECT * FROM students_tb LEFT JOIN classes_tb ON students_tb.ClassID=classes_tb.ClassID;+-----------+--------+------+--------+---------+---------+--------+-----------+| StudentID | Name | Age | Gender | ClassID | ClassID | Class | TeacherID |+-----------+--------+------+--------+---------+---------+--------+-----------+| 1 | Tom | 17 | M | 1 | 1 | class1 | 5 || 2 | Jack | 18 | M | 3 | 3 | class3 | 5 || 3 | Lucy | 21 | F | 6 | 6 | class6 | 1 || 4 | Jimima | 15 | F | 4 | 4 | class4 | 2 || 5 | Jimmy | 30 | M | 9 | NULL | NULL | NULL || 6 | Jim | 26 | M | 7 | NULL | NULL | NULL || 7 | Cora | 25 | F | 6 | 6 | class6 | 1 || 8 | Echo | 58 | F | 7 | NULL | NULL | NULL || 9 | 张三 | 47 | M | 3 | 3 | class3 | 5 |+-----------+--------+------+--------+---------+---------+--------+-----------+ |
右外联结（语法：左表 RIGHT JION 右表 ON 条件）
显示各个班级有哪些同学，如果这个班级没有同学就留空：
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mysql> SELECT * FROM students_tb RIGHT JOIN classes_tb ON students_tb.ClassID=classes_tb.ClassID;+-----------+--------+------+--------+---------+---------+--------+-----------+| StudentID | Name | Age | Gender | ClassID | ClassID | Class | TeacherID |+-----------+--------+------+--------+---------+---------+--------+-----------+| 1 | Tom | 17 | M | 1 | 1 | class1 | 5 || NULL | NULL | NULL | NULL | NULL | 2 | class2 | 2 || 2 | Jack | 18 | M | 3 | 3 | class3 | 5 || 9 | 张三 | 47 | M | 3 | 3 | class3 | 5 || 4 | Jimima | 15 | F | 4 | 4 | class4 | 2 || NULL | NULL | NULL | NULL | NULL | 5 | class5 | 4 || 3 | Lucy | 21 | F | 6 | 6 | class6 | 1 || 7 | Cora | 25 | F | 6 | 6 | class6 | 1 |+-----------+--------+------+--------+---------+---------+--------+-----------+ |
全外联结：
mysql无全外联结
6.2.2、联合查询：UNION
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mysql> SELECT Name,Age FROM teacher_tb WHERE Age > 40 UNION SELECT Name,Age FROM students_tb WHERE Age > 30;+-----------+------+| Name | Age |+-----------+------+| Ying hui | 50 || Feng bing | 46 || Shun bin | 68 || Echo | 58 || 张三 | 47 |+-----------+------+ |
查询同学所对应的负责老师：
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mysql> SELECT students_tb.Name AS student_name,teacher_tb.Name AS teacher_name FROM students_tb,classes_tb,teacher_tb WHERE students_tb.ClassID=classes_tb.ClassID AND classes_tb.TeacherID=teacher_tb.TeacherID;+--------------+----------------+| student_name | teacher_name |+--------------+----------------+| Tom | Feng bing || Jack | Feng bing || 张三 | Feng bing || Jimima | Zhang shanfeng || Lucy | Wang baoqiang || Cora | Wang baoqiang |+--------------+----------------+ |
6.2.3、内联结：INNER JON...ON
语法：
表1 AS 别名1 INNER JOIN 表1 AS 别名2 ON 别名1.字段=别名2.字段
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mysql> SELECT * FROM students_tb AS s INNER JOIN classes_tb AS c ON s.ClassID = c.ClassID;+-----------+--------+------+--------+---------+---------+--------+-----------+| StudentID | Name | Age | Gender | ClassID | ClassID | Class | TeacherID |+-----------+--------+------+--------+---------+---------+--------+-----------+| 1 | Tom | 17 | M | 1 | 1 | class1 | 5 || 2 | Jack | 18 | M | 3 | 3 | class3 | 5 || 12 | 张三 | 47 | M | 3 | 3 | class3 | 5 || 4 | Jimima | 15 | F | 4 | 4 | class4 | 2 || 3 | Lucy | 21 | F | 6 | 6 | class6 | 1 || 10 | Cora | 25 | F | 6 | 6 | class6 | 1 |+-----------+--------+------+--------+---------+---------+--------+-----------+ |
6.3、子查询
6.3.1、WHERE子查询
显示年龄大于平均年龄的学生：
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mysql> SELECT Name,Age FROM students_tb WHERE Age > (SELECT AVG(Age) FROM students_tb);+--------+------+| Name | Age |+--------+------+| Jimmy | 30 || Echo | 58 || 张三 | 47 |+--------+------+ |
查询学生表中给定来存在的班级的学生信息：
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mysql> SELECT * FROM classes_tb;+---------+--------+-----------+| ClassID | Class | TeacherID |+---------+--------+-----------+| 1 | class1 | 5 || 2 | class2 | 2 || 3 | class3 | 5 || 4 | class4 | 2 || 5 | class5 | 4 || 6 | class6 | 1 |+---------+--------+-----------+#只有6个班级mysql> SELECT Name,ClassID FROM students_tb WHERE ClassID NOT IN (SELECT ClassID FROM classes_tb);+-------+---------+| Name | ClassID |+-------+---------+| Jimmy | 9 || Jim | 7 || Echo | 7 |+-------+---------+#7和9这两个班级是不存在的 |
查询各个班级中同学年龄大于全校平均年龄的同学的个数：
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mysql> SELECT ClassID,COUNT(Name) FROM students_tb WHERE Age > (SELECT AVG(Age) FROM students_tb) GROUP BY ClassID;+---------+-------------+| ClassID | COUNT(Name) |+---------+-------------+| 3 | 1 || 7 | 1 || 9 | 1 |+---------+-------------+mysql> SELECT Name,Age,ClassID FROM students_tb WHERE Age > (SELECT AVG(Age) FROM students_tb); #验证上边的结果+--------+------+---------+| Name | Age | ClassID |+--------+------+---------+| Jimmy | 30 | 9 || Echo | 58 | 7 || 张三 | 47 | 3 |+--------+------+---------+ |
6.3.2、FROM子查询：
查询表中男性同学中年龄大于20的：
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mysql> SELECT * FROM (SELECT Name,Age,Gender FROM students_tb WHERE Gender= ‘M‘ ) AS S WHERE Age > 20;+--------+------+--------+| Name | Age | Gender |+--------+------+--------+| Jimmy | 30 | M || Jim | 26 | M || 张三 | 47 | M |+--------+------+--------+ |
mysql中对子查询优化很有限，建议不要使用子查询，可改为其他的简单查询或联合查询。
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原文地址：http://www.cnblogs.com/quyanan/p/4446982.html
