MySQL进行查询结果求和的五种方法详解

SELECT SUM(amount) AS total_sales FROM sales;

SELECT MONTH(date), SUM(amount) AS monthly_sales 
FROM sales 
GROUP BY MONTH(date);

SELECT SUM(amount) AS total_sales FROM sales WHERE salesman_id = 101;

SELECT 
    IFNULL(MONTH(date), 'Total') AS Month, 
    SUM(amount) AS monthly_sales 
FROM 
    sales 
GROUP BY 
    MONTH(date) WITH ROLLUP;

SELECT 
    customers.name, 
    SUM(orders.amount) AS total_order_amount 
FROM 
    customers 
JOIN 
    orders ON customers.id = orders.customer_id 
GROUP BY 
    customers.name;

select * from Info --查所有数据
select Code,Name from Info --查指定列的数据
select Code as '代号',Name as '姓名' from Info --给列指定别名

select * from Info where Code='p001'
select * from Info where Sex='true' and Nation='n001' --多条件并的关系
select * from Info where Sex='true' or Nation='n001' --多条件或的关系

select * from Car where Price>40 and Price<50
select * from Car where Price between 40 and 50

select * from Car where Code in ('c001','c005','c010','c015')
select * from Car where Code not in ('c001','c005','c010','c015')

select * from Car where Name like '%宝马%' --查包含宝马的
select * from Car where Name like '宝马%' --查以宝马开头的
select * from Car where Name like '%宝马' --查以宝马结尾的
select * from Car where Name like '宝马' --查等于宝马的
select * from Car where Name like '__E%' --查第三个字符是E的

select * from Car order by Price asc --以价格升序排列
select * from Car order by Price desc --以价格降序排列
select * from Car order by Oil desc,Price asc --以两个字段排序，前面的是主条件后面的是次要条件

select top 5 * from Car
select top 5 * from Car where Code not in (select top 5 Code from Car)

select top row * from Car where Code not in (select top (page-1)*row Code from Car)

select distinct Brand from Car

select Brand from Car group by Brand having count(*)>2

select count(*) from Car --查询所有数据条数
select count(Code) from Car --查询所有数据条数
select sum(Price) from Car --求和
select avg(Price) from Car --求平均
select max(Price) from Car --求最大值
select min(Price) from Car --求最小值

select * from Info,Nation --形成笛卡尔积
select * from Info,Nation where Info.Nation = Nation.Code
select Info.Code,Info.Name,Sex,Nation.Name,Birthday from Info,Nation where Info.Nation = Nation.Code
select * from Info join Nation on Info.Nation = Nation.Code --join on 的形式

select Code,Name from Info
union
select Code,Name from Nation

--查询民族为汉族的所有人员信息
select * from Info where Nation = (select Code from Nation where Name = '汉族')

--查询系列是宝马5系的所有汽车信息
select * from Car where Brand =(select Brand_Code from Brand where Brand_Name = '宝马5系')

--查找油耗低于该系列平均油耗的汽车
select * from Car where Oil
select avg(Oil) from Car where Brand = (该系列)
select * from Car a where Oil