一、介绍
在MySQL管理软件中,可以通过SQL语句中的DML语言来实现数据的操作,包括
- 使用INSERT实现数据的插入
- UPDATE实现数据的更新
- 使用DELETE实现数据的删除
- 使用SELECT查询数据以及。
二、插入数据
1. 插入完整数据(顺序插入) 语法一: INSERT INTO 表名(字段1,字段2,字段3…字段n) VALUES(值1,值2,值3…值n); 语法二: INSERT INTO 表名 VALUES (值1,值2,值3…值n); 2. 指定字段插入数据 语法: INSERT INTO 表名(字段1,字段2,字段3…) VALUES (值1,值2,值3…); 3. 插入多条记录 语法: INSERT INTO 表名 VALUES (值1,值2,值3…值n), (值1,值2,值3…值n), (值1,值2,值3…值n); 4. 插入查询结果 语法: INSERT INTO 表名(字段1,字段2,字段3…字段n) SELECT (字段1,字段2,字段3…字段n) FROM 表2 WHERE …;
三、更新数据
语法: UPDATE 表名 SET 字段1=值1, 字段2=值2, WHERE CONDITION;
四、删除数据
语法: DELETE FROM 表名 WHERE CONITION;
五、查询数据
单表查询语法: SELECT 字段1,字段2... FROM 表名 WHERE 条件 GROUP BY field HAVING 筛选 ORDER BY field LIMIT 限制条数 多表查询语法: SELECT 字段列表 FROM 表1 INNER|LEFT|RIGHT JOIN 表2 ON 表1.字段 = 表2.字段;
select关键字的定义顺序:
SELECT DISTINCT <select_list> FROM <left_table> <join_type> JOIN <right_table> ON <join_condition> WHERE <where_condition> GROUP BY <group_by_list> HAVING <having_condition> ORDER BY <order_by_condition> LIMIT <limit_number>
select关键字的执行顺序:
(7) SELECT (8) DISTINCT <select_list> (1) FROM <left_table> (3) <join_type> JOIN <right_table> (2) ON <join_condition> (4) WHERE <where_condition> (5) GROUP BY <group_by_list> (6) HAVING <having_condition> (9) ORDER BY <order_by_condition> (10) LIMIT <limit_number>
(一)、单表查询
company.employee 员工id id int 姓名 emp_name varchar 性别 sex enum 年龄 age int 入职日期 hire_date date 岗位 post varchar 职位描述 post_comment varchar 薪水 salary double 办公室 office int 部门编号 depart_id int #创建表 create table employee( id int not null unique auto_increment, name varchar(20) not null, sex enum('male','female') not null default 'male', #大部分是男的 age int(3) unsigned not null default 28, hire_date date not null, post varchar(50), post_comment varchar(100), salary double(15,2), office int, #一个部门一个屋子 depart_id int ); #插入记录 #三个部门:教学,销售,运营 insert into employee(name,sex,age,hire_date,post,salary,office,depart_id) values ('egon','male',18,'20170301','老男孩驻沙河办事处外交大使',7300.33,401,1), #以下是教学部 ('alex','male',78,'20150302','teacher',1000000.31,401,1), ('wupeiqi','male',81,'20130305','teacher',8300,401,1), ('yuanhao','male',73,'20140701','teacher',3500,401,1), ('liwenzhou','male',28,'20121101','teacher',2100,401,1), ('jingliyang','female',18,'20110211','teacher',9000,401,1), ('jinxin','male',18,'19000301','teacher',30000,401,1), ('成龙','male',48,'20101111','teacher',10000,401,1), ('歪歪','female',48,'20150311','sale',3000.13,402,2),#以下是销售部门 ('丫丫','female',38,'20101101','sale',2000.35,402,2), ('丁丁','female',18,'20110312','sale',1000.37,402,2), ('星星','female',18,'20160513','sale',3000.29,402,2), ('格格','female',28,'20170127','sale',4000.33,402,2), ('张野','male',28,'20160311','operation',10000.13,403,3), #以下是运营部门 ('程咬金','male',18,'19970312','operation',20000,403,3), ('程咬银','female',18,'20130311','operation',19000,403,3), ('程咬铜','male',18,'20150411','operation',18000,403,3), ('程咬铁','female',18,'20140512','operation',17000,403,3) ; #ps:如果在windows系统中,插入中文字符,select的结果为空白,可以将所有字符编码统一设置成gbk
简单查询:
#简单查询 SELECT id,name,sex,age,hire_date,post,post_comment,salary,office,depart_id FROM employee; SELECT * FROM employee; SELECT name,salary FROM employee; #避免重复DISTINCT SELECT DISTINCT post FROM employee; #通过四则运算查询 SELECT name, salary*12 FROM employee; SELECT name, salary*12 AS Annual_salary FROM employee; SELECT name, salary*12 Annual_salary FROM employee; #定义显示格式 CONCAT() 函数用于连接字符串 SELECT CONCAT('姓名: ',name,' 年薪: ', salary*12) AS Annual_salary FROM employee; CONCAT_WS() 第一个参数为分隔符 SELECT CONCAT_WS(':',name,salary*12) AS Annual_salary FROM employee; 结合CASE语句: SELECT ( CASE WHEN NAME = 'egon' THEN NAME WHEN NAME = 'alex' THEN CONCAT(name,'_BIGSB') ELSE concat(NAME, 'SB') END ) as new_name FROM emp;
1.where约束:
where字句中可以使用:
1. 比较运算符:> < >= <= <> !=
2. between 80 and 100 值在10到20之间
3. in(10,20,30) 值是10或20或30
4. like 'abc%'
%表示任意多字符
_表示一个字符
5. 逻辑运算符:在多个条件直接可以使用逻辑运算符 not and or
#1:单条件查询 SELECT name FROM employee WHERE post='sale'; #2:多条件查询 SELECT name,salary FROM employee WHERE post='teacher' AND salary>10000; #3:关键字BETWEEN AND SELECT name,salary FROM employee WHERE salary BETWEEN 10000 AND 20000; SELECT name,salary FROM employee WHERE salary NOT BETWEEN 10000 AND 20000; #4:关键字IS NULL(判断某个字段是否为NULL不能用等号,需要用IS) SELECT name,post_comment FROM employee WHERE post_comment IS NULL; SELECT name,post_comment FROM employee WHERE post_comment IS NOT NULL; SELECT name,post_comment FROM employee WHERE post_comment=''; 注意''是空字符串,不是null ps: 执行 update employee set post_comment='' where id=2; 再用上条查看,就会有结果了 #5:关键字IN集合查询 SELECT name,salary FROM employee WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000 ; SELECT name,salary FROM employee WHERE salary IN (3000,3500,4000,9000) ; SELECT name,salary FROM employee WHERE salary NOT IN (3000,3500,4000,9000) ; #6:关键字LIKE模糊查询 通配符’%’ SELECT * FROM employee WHERE name LIKE 'eg%'; 通配符’_’ SELECT * FROM employee WHERE name LIKE 'al__';
2.正则表达式查询:
SELECT * FROM employee WHERE name REGEXP 'on$'; 除了模糊查询 还可以使用正则表达式查询 小结:对字符串匹配的方式 WHERE name = 'onclose'; WHERE name LIKE 'on%'; WHERE name REGEXP 'on$';
3.group by 分组:
#查看MySQL 5.7默认的sql_mode如下: mysql> select @@global.sql_mode; ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION #!!!注意 ONLY_FULL_GROUP_BY的语义就是确定select target list中的所有列的值都是明确语义,简单的说来,在ONLY_FULL_GROUP_BY模式下,target list中的值要么是来自于聚集函数的结果,要么是来自于group by list中的表达式的值。 #设置sql_mole如下操作(我们可以去掉ONLY_FULL_GROUP_BY模式): mysql> set global sql_mode='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION';
语法:
单独使用GROUP BY关键字分组 SELECT post FROM employee GROUP BY post; 注意:我们按照post字段分组,那么select查询的字段只能是post,想要获取组内的其他相关信息,需要借助函数 GROUP BY关键字和GROUP_CONCAT()函数一起使用 SELECT post,GROUP_CONCAT(name) FROM employee GROUP BY post;#按照岗位分组,并查看组内成员名 SELECT post,GROUP_CONCAT(name) as emp_members FROM employee GROUP BY post; GROUP BY与聚合函数一起使用 select post,count(id) as count from employee group by post;#按照岗位分组,并查看每个组有多少人
#如果没有设置ONLY_FULL_GROUP_BY,也可以有结果,默认都是组内的第一条记录,但其实这是没有意义的 mysql> set global sql_mode='ONLY_FULL_GROUP_BY'; Query OK, 0 rows affected (0.00 sec) mysql> quit #设置成功后,一定要退出,然后重新登录方可生效 Bye mysql> use db1; Database changed mysql> select * from emp group by post; #报错 ERROR 1055 (42000): 'db1.emp.id' isn't in GROUP BY mysql> select post,count(id) from emp group by post; #只能查看分组依据和使用聚合函数
4.聚合函数:
#强调:聚合函数聚合的是组的内容,若是没有分组,则默认一组 示例: SELECT COUNT(*) FROM employee; SELECT COUNT(*) FROM employee WHERE depart_id=1; SELECT MAX(salary) FROM employee; SELECT MIN(salary) FROM employee; SELECT AVG(salary) FROM employee; SELECT SUM(salary) FROM employee; SELECT SUM(salary) FROM employee WHERE depart_id=3;
5.having过滤:
“Where” 是一个约束声明,使用Where来约束来自数据库的数据,Where是在结果返回之前起作用的,且Where中不能使用聚合函数。
“Having”是一个过滤声明,是在查询返回结果集以后对查询结果进行的过滤操作,在Having中可以使用聚合函数。
执行优先级从高到低:where > group by > having
注:用having就一定要用group by, 用group by不一定要有having。只要条件里面的字段, 不是表里面原先有的字段就需要用having。
6.order by 排序:
按单列排序 SELECT * FROM employee ORDER BY salary;#默认ASC升序 SELECT * FROM employee ORDER BY salary ASC; SELECT * FROM employee ORDER BY salary DESC;#降序 按多列排序:先按照age排序,如果年纪相同,则按照薪资排序 SELECT * from employee ORDER BY age, salary DESC;
7.limit 限制查询记录数:
示例: SELECT * FROM employee ORDER BY salary DESC LIMIT 3; #默认初始位置为0 ,查询3条数据 SELECT * FROM employee ORDER BY salary DESC LIMIT 0,5; #从第0开始,即先查询出第一条,然后包含这一条在内往后查5条 SELECT * FROM employee ORDER BY salary DESC LIMIT 5,5; #从第5开始,即先查询出第6条,然后包含这一条在内往后查5条
(二)、多表查询
SELECT 字段列表 FROM 表1 INNER|LEFT|RIGHT JOIN 表2 ON 表1.字段 = 表2.字段;
1.交叉连接(笛卡尔积):
交叉连接返回左表中的所有行,左表中的每一行与右表中的所有行组合,结果集的行数是两个表的行数的乘积。(效率最低)
mysql> select * from employee,department; +----+------------+--------+------+--------+------+--------------+ | id | name | sex | age | dep_id | id | name | +----+------------+--------+------+--------+------+--------------+ | 1 | A | male | 18 | 200 | 200 | 技术 | | 1 | A | male | 18 | 200 | 201 | 人力资源 | | 1 | A | male | 18 | 200 | 202 | 销售 | | 1 | A | male | 18 | 200 | 203 | 运营 | | 2 | B | female | 48 | 201 | 200 | 技术 | | 2 | B | female | 48 | 201 | 201 | 人力资源 | | 2 | B | female | 48 | 201 | 202 | 销售 | | 2 | B | female | 48 | 201 | 203 | 运营 | | 3 | C | male | 38 | 201 | 200 | 技术 | | 3 | C | male | 38 | 201 | 201 | 人力资源 | | 3 | C | male | 38 | 201 | 202 | 销售 | | 3 | C | male | 38 | 201 | 203 | 运营 | +----+------------+--------+------+--------+------+--------------+
2.内连接:只连接匹配的行
INNER JOIN(内连接),也成为自然连接,找两张表共有的部分,相当于利用条件从笛卡尔积结果中筛选出了正确的结果,内连接是从结果中删除其他被连接表中没有匹配行的所有行,所以内连接可能会丢失信息。
mysql> select employee.id,employee.name,employee.age,employee.sex,department.name from employee inner join department on employee.dep_id=department.id; +----+-----------+------+--------+--------------+ | id | name | age | sex | name | +----+-----------+------+--------+--------------+ | 1 | A | 18 | male | 技术 | | 2 | B | 48 | female | 人力资源 | | 3 | C | 38 | male | 人力资源 | +----+-----------+------+--------+--------------+ #上述sql等同于 mysql> select employee.id,employee.name,employee.age,employee.sex,department.name from employee,department where employee.dep_id=department.id;
3.外连接之左连接:
返回左表中的所有行,如果左表中行在右表中没有匹配行,则结果中右表中的列返回空值。
select employee.id,employee.name,department.name as depart_name from employee left join department on employee.dep_id=department.id;
4.外连接之右连接:
与左连接正好相反,返回右表中的所有行,如果右表中行在左表中没有匹配行,则结果中左表中的列返回空值。
select employee.id,employee.name,department.name as depart_name from employee right join department on employee.dep_id=department.id;
5.全外连接:显示左右两个表全部记录
在内连接的基础上增加左边有右边没有的,右边有左边没有的。是左外连接和右外连接的并集。
注:mysql不支持全外连接full join 但是可以用下面的方式实现(union与union all的区别:union会去掉相同的纪录)
select * from employee left join department on employee.dep_id = department.id union select * from employee right join department on employee.dep_id = department.id ;
(三)、子查询
#1:子查询是将一个查询语句嵌套在另一个查询语句中。 #2:内层查询语句的查询结果,可以为外层查询语句提供查询条件。 #3:子查询中可以包含:IN、NOT IN、ANY、ALL、EXISTS 和 NOT EXISTS等关键字 #4:还可以包含比较运算符:= 、 !=、> 、<等
1.带in关键字的子查询
#查询平均年龄在25岁以上的部门名 select id,name from department where id in (select dep_id from employee group by dep_id having avg(age) > 25); #查看技术部员工姓名 select name from employee where dep_id in (select id from department where name='技术'); #查看不足1人的部门名(子查询得到的是有人的部门id) select name from department where id not in (select distinct dep_id from employee);
2.带比较运算符的子查询
#查询大于部门内平均年龄的员工名、年龄 select t1.name,t1.age from emp t1 inner join (select dep_id,avg(age) avg_age from emp group by dep_id) t2 on t1.dep_id = t2.dep_id where t1.age > t2.avg_age;
3.带exists关键字的子查询
#department表中存在dept_id=203,Ture mysql> select * from employee -> where exists -> (select id from department where id=200); #department表中存在dept_id=205,False mysql> select * from employee -> where exists -> (select id from department where id=204); Empty set (0.00 sec)
六、权限管理
#授权表 user #该表放行的权限,针对:所有数据,所有库下所有表,以及表下的所有字段 db #该表放行的权限,针对:某一数据库,该数据库下的所有表,以及表下的所有字段 tables_priv #该表放行的权限。针对:某一张表,以及该表下的所有字段 columns_priv #该表放行的权限,针对:某一个字段
#查看自己的权限
show grants; #创建用户 create user 用户名@"主机地址" identified by "密码"; create user 'A'@'1127.0.0.1' identified by '123'; create user 'B'@'192.168.1.%' identified by '123';#指定ip create user 'C'@'%' identified by '123';#任意用户 #授权:对文件夹,对文件,对文件某一字段的权限 查看帮助:help grant 常用权限有:select,update,alter,delete all可以代表除了grant之外的所有权限 语法: grant [权限的名称 select insert.... | all ] on 数据库.表名 to 用户名@主机地址; 特点: 如果授权时,用户不存在则直接自动创建用户 #针对所有库的授权:*.* grant select on *.* to 'A'@'localhost' identified by '123'; #只在user表中可以查到A用户的select权限被设置为Y
没有 Grant_priv(授权)的权限 #针对某一数据库:db1.* grant select on db1.* to 'B'@'%' identified by '123'; #只在db表中可以查到B用户的select权限被设置为Y #针对某一个表:db1.t1 grant select on db1.t1 to 'C'@'%' identified by '123'; #只在tables_priv表中可以查到C用户的select权限 #针对某一个字段: grant select (id,name),update (age) on db1.t3 to 'D'@'localhost' identified by '123'; #可以在tables_priv和columns_priv中看到相应的权限 #删除权限 revoke 权限的名称 on 数据库.表名 from 用户名@"主机名" ; revoke select on db1.* from 'A'@'%'; #删除用户 drop user 用户名@"主机地址";
注:添加权限之后,要记得刷新权限
flush privileges;
如果要让用户拥有所有权限,可以执行下面的命令:
grant [权限的名称 select insert.... | all ] on 数据库.表名 to 用户名@主机地址 with grant option; with grant option 这个用户可以将他有的权限授予别的账户
焚膏油以继晷,恒兀兀以穷年。