标签：简单 这一 大于 四则运算 初始 group ext 定义 closed
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 …;
语法： UPDATE 表名 SET 字段1=值1, 字段2=值2 WHERE CONDITION; 示例： UPDATE mysql.user SET password=password(‘123’) where user=’root’ and host=’localhost’;
语法：
DELETE FROM 表名 WHERE CONITION;
示例：
DELETE FROM mysql.user WHERE password=’密码’;
#查询的语法 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 #关键字的执行优先级(重点) from #查找到表 where #使用where指定约束条件，去文件或表中取出记录 group by #使用group by 讲取出的记录进行分组，若没有group by 则整体作为一组 having #使用having 对分组的结果进行整体的过滤 select #执行select语句 distinct #使用distinct 去掉重复的记录 order by #使用order by将结果按条件进行分类 limit #限制结果的显示条数
#定义示例表 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‘, 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, depart_id int ); #查看表结构 mysql> desc employee; +--------------+-----------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +--------------+-----------------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(20) | NO | | NULL | | | sex | enum(‘male‘,‘female‘) | NO | | male | | | age | int(3) unsigned | NO | | 28 | | | hire_date | date | NO | | NULL | | | post | varchar(50) | YES | | NULL | | | post_comment | varchar(100) | YES | | NULL | | | salary | double(15,2) | YES | | NULL | | | office | int(11) | YES | | NULL | | | depart_id | int(11) | YES | | NULL | | +--------------+-----------------------+------+-----+---------+----------------+ #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 (‘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), (‘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), (‘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) ; #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;
#约束条件
比较运算符：> < >= <= <> != between 80 and 100 值在10到20之间 in(80,90,100) 值是10或20或30 ike ‘egon%‘ pattern可以是%或_， %表示任意多字符 _表示一个字符 逻辑运算符：在多个条件直接可以使用逻辑运算符 and or not
简单示例
#单条件查询 SELECT name FROM employee WHERE post=‘sale‘; #多条件查询 SELECT name,salary FROM employee WHERE post=‘teacher‘ AND salary>10000; #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; #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 #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) ; #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__‘;
分组发生在where之后，即分组是基于where之后得到的记录而进行的
分组指的是：将所有记录按照某个相同字段进行归类，比如针对员工信息表的职位分组，或者按照性别进行分组等
ps：可以按照任意字段分组，但是分组完毕后，比如group by post，只能查看post字段，如果想查看组内信息，需要借助于聚合函数
简单示例
#单独使用GROUP BY关键字分组 SELECT post FROM employee GROUP BY post; ps: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
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;
#HAVING与WHERE区别 执行优先级从高到低：where > group by > having Where 发生在分组group by之前，因而Where中可以有任意字段，但是绝对不能使用聚合函数。 Having发生在分组group by之后，因而Having中可以使用分组的字段，无法直接取到其他字段,可以使用聚合函数
简单示例
#查询各岗位内包含的员工个数小于2的岗位名、岗位内包含员工名字、个数 select post,group_concat(name),count(id) from employee group by post having count(id) < 2; #查询各岗位平均薪资大于10000的岗位名、平均工资 select post,avg(salary) from employee group by post having avg(salary) > 10000; #查询各岗位平均薪资大于10000且小于20000的岗位名、平均工资 select post,avg(salary) from employee group by post having avg(salary) > 10000 and avg(salary) <20000;
#按单列排序 SELECT * FROM employee ORDER BY salary; SELECT * FROM employee ORDER BY salary ASC; SELECT * FROM employee ORDER BY salary DESC; #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;
简单示例
#查询所有员工信息，先按照age升序排序，如果age相同则按照hire_date降序排序 select * from employee ORDER BY age asc,hire_date desc; #查询各岗位平均薪资大于10000的岗位名、平均工资,结果按平均薪资升序排列 select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) asc; #查询各岗位平均薪资大于10000的岗位名、平均工资,结果按平均薪资降序排列、 select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) desc;
SELECT * FROM employee ORDER BY salary DESC LIMIT 3; #默认初始位置为0 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
简单示例
#分页显示，每页五条 select * from employee limit 0,5; select * from employee limit 5,5; select * from employee limit 10,5;
SELECT * FROM employee WHERE name REGEXP ‘^ale‘; SELECT * FROM employee WHERE name REGEXP ‘on$‘; SELECT * FROM employee WHERE name REGEXP ‘m{2}‘; #字符串匹配的方式 WHERE name = ‘egon‘; WHERE name LIKE ‘yua%‘; WHERE name REGEXP ‘on$‘;
简单示例
#查看所有员工中名字是jin开头，n或者g结果的员工信息 select * from employee where name regexp ‘^jin.*[gn]$‘;
标签：简单 这一 大于 四则运算 初始 group ext 定义 closed
原文地址：https://www.cnblogs.com/dragon-123/p/10383725.html
