MYSQL中的多类型查询及高级查询操作

Posted 2020-10-02 WORSHIP亚萨

　　离散查询
select * from car where price=30 or price=40 or price=50 or price=60;
select * from car where price in(30,40,50,60)取出数据
select * from car where price not in(30,40,50,60)去掉数据

　　聚合函数（统计查询）
select count(*) from car
select count(code) from car #取所有的数据条数
select sum(price) from car #求价格总和
select avg(price) from car #求价格的平均值
select max(price) from car #求最大值
select min(price) from car #求最小值

　　分页查询
select * from car limit 0,10  #分页查询，跳过几条数据(0)取几条(10)
规定一个每页显示的条数：m
当前页数：n]
select * from car limit (n-1)*m,m

　　去重查询
select distinct brand from car

　　分组查询
查询汽车表中，每个系列下汽车的数量
select brand,count(*) from car group by brand
分组之后，只能查询该列或聚合函数

取该系列价格平均值大于40的系列代号
select brand from car group by brand having（加条件） avg(price)>40

取该系列油耗最大值大于8的系列代号
select brand from car group by brand having max(oil)>8

高级查询

（1）连接查询
SELECT t1.`Name`,t2.Brand_Name FROM brand t2,car t1 -- 笛卡尔乘积
WHERE t2.Brand = t1.Brand
-- 多表连接查询
SELECT t1.`Name`,t2.Brand_Name,t3.prod_name  

FROM car t1
LEFT JOIN brand t2
ON t1.Brand = t2.Brand

LEFT JOIN productor t3 ON t2.Prod = t3.Prod
（2） 联合查询 字段数必须一样
SELECT `Name`,Price FROM car
UNION
SELECT Brand_Name,Brand_Memo FROM brand
（3）子查询
SELECT * FROM car
WHERE car.brand in
(SELECT Brand FROM brand WHERE Prod = ‘p001‘)