数据库基本查询与高级查询

一、基本查询：

select * from Fruit --查所有
select Name,Source from Fruit --查特定列

select Ids ‘代号‘,Name ‘名称‘,Price ‘价格‘,Source ‘产地‘ from Fruit -- 修改列名

select * from Fruit where Ids=‘K006‘
select * from Fruit where Price=2.4 and Source=‘烟台‘ -- 查指定行按条件查

select * from Fruit where Price between 2.0 and 4.0 --查指定行按范围查

select * from Fruit where Numbers in (90,80,70)--查指定行，离散查

select distinct Numbers from Fruit --去重查询

select * from News

select * from News where title like ‘%户口‘ --模糊查询，查以户口结尾的
select * from News where title like ‘路飞%‘ --模糊查询，查以路飞开头的
select * from News where title like ‘%路飞%‘ --模糊查询，查以包含路飞的
select * from News where title like ‘%外币货_‘--模糊查询，查外币货之后只有一个字符的

select * from Fruit order by Numbers asc --按照Numbers列升序排，如果不加asc默认以升序排
select * from Fruit order by Numbers desc --按照Numbers列降序排
select * from Fruit order by Numbers,Price --先按照Numbers排，然后再按照Price排

select COUNT(*) from Fruit --返回Fruit表里面有多少条数据
select AVG(Numbers)from Fruit --返回某一列的平均值
select SUM(Numbers) from Fruit --返回某一列的所有数据和
select MAX(Numbers) from Fruit --返回某一列中的最大值
select MIN(Numbers) from Fruit --返回某一列中的最小值

select *,(Price*0.8) as ‘折后价格‘ from Fruit --加一列数据库中没有的列，这里是加了8折后的价格列

select Numbers, COUNT(*) from Fruit group by Numbers --根据某一列分组，求出该组内成员的个数
select Numbers, COUNT(*) from Fruit group by Numbers having COUNT(*)>1--根据某一列分组，求出该组内成员的个数,返回成员个数大于1的

二、高级查询：

--连接查询
select * from Info,Nation -- 形成笛卡尔积
select * from Info,Nation where Nation.Code=Info.Nation  

--join on 内连接
select * from Info join Nation on Info.Nation = Nation.Code

--查哪位学生的哪一门课考了多少分
select student.sname,course.cname,score.degree from student join score on score.sno=student.sno join course on course.cno = score.cno

--右连接,右边表必须显示全,如果在左边表没有与之对应的信息,则补空值
select * from Info right join Nation on Info.Nation=Nation.Code
--左连接,左边表必须显示全,如果在右边表没有与之对应的信息,则补空值
select * from Info left join Nation on Info.Nation=Nation.Code
--全连接，左右两边的表都显示完全
select * from Info full join Nation on Info.Nation=Nation.Code

--联合查询,对于查出的两个或多个结构相同的表联合显示
select Code,Name from Info
union
select InfoCode,Name from Family

--------子查询------------------
--子查询的结果当做父查询的条件
select * from Info
--无关子查询，子查询执行是独立的，和父查询是没有关系的（没有用到父查询的东西）
select * from Info where year(Birthday)=(
select YEAR(Birthday) from info where Code=‘p005‘)

--相关子查询
select * from teacher
--求计算机系和电子工程系不同职称的老师信息
select * from teacher t1 where depart=‘计算机系‘ and not exists(
select * from teacher t2 where depart=‘电子工程系‘ and t1.prof = t2.prof)
union
select * from teacher t1 where depart=‘电子工程系‘
and not exists(
select * from teacher t2 where depart=‘计算机系‘ and t1.prof = t2.prof
)

--查询除了每门课最高分之外的其他学生信息。
select * from score

select * from score where degree not in(select MAX(degree) from score group by cno)--错误

select * from score s1 where degree not in(
select MAX(degree) from score s2 group by cno having s1.cno = s2.cno
)

--select * from score where degree not in(86,75)

--分页
select * from Car

select top 5 * from Car -- 前5条数据，第一页
select top 5 * from Car where Code not in(
select top 5 Code from Car
) -- 第二页的数据

select top 5 * from Car where Code not in(
select top 10 Code from Car
) --第三页的数据

select top 5 * from Car where Code not in(
select top (5*2) Code from Car
) 

select ceiling(COUNT(*)/5) from Car --求总页数

select * from Car where 条件 limit 跳过几条数据，取几条数据 --mysql里面的分页