MySql各種查詢

1.簡單查詢

　　select * from info;

　　select Code as '代號',name as '姓名' from info;

2.條件查詢

　　select * from car where code = 'c002';

　　select * from car where brand ='b001' and power = 130; #或用or

3.模糊查詢

　　select * from car where name like '%奧迪%';  %代表任意多個字符包括0個 _代表一個字符

4.排序查詢

　　select * from car order by brand, powers desc; asc升序默認可以不寫

5。范圍查詢

　　select * from car where price between 40 and 60;

6.離散查詢

　　select * from car where code in('coo1','c003','c005','c007');

　　select * from car where code not in('coo1','c003','c005','c007');

7.統計查詢（聚合函數）

　　select count(code) from car;　　查詢數據條數也可以count(*)這么寫，性能低

　　select sum(price) from car;　　求和

　　select max(code) from car;　　最大　　

　　select min(brand) from car;　　最小

　　select avg(price) from car;　　平均

　　select year(brithday) from dtudent; # 取出生年月的年

8.分頁查詢

　　select * from Car limit (n-1)*5,5  #第n頁，每頁顯示五條數據

9.去重查詢

　　select distinct Brand from Car

10.分組查詢　

　　select brand,count(*),Brand from Car group by Brand 　　#把brand列的相同值組合起來，並這一條數據對該列或或其他列進行操作例如求平均值
　　select Brand from Car group by Brand having count(*)>3 #分組之后根據條件查詢使用having 不使用where

 

高級查詢

1.連接查詢，對列的擴展

select * from Info,Nation #形成笛卡爾積
select Info.Code,Info.Name,Info.Sex,Nation.Name,Info.Birthday from Info,Nation where Info.Nation = Nation.Code

select * from Info join Nation
select * from Info join Nation on Info.Nation = Nation.Code

2.聯合查詢，對行的擴展

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

3.子查詢

(1)無關子查詢

外層查詢 (里層查詢)
子查詢的結果當做父查詢的條件

子查詢：select Code from Nation where Name='漢族'
父查詢：select * from Info where Nation = ''

select * from Info where Nation = (select Code from Nation where Name='漢族')

(2)相關子查詢
查詢汽車表中油耗低於該系列平均油耗的所有汽車信息

父查詢：select * from Car where Oil<(該系列平均油耗)
子查詢：select avg(Oil) from Car where Brand = '某個系列'

select * from Car a where Oil<(select avg(Oil) from Car b where b.Brand = a.Brand )