select * from TblPerson
select * from PhoneNum
select * from PhoneType
select pid,pname,pcellPhone,ptname,ptid from PhoneNum pn inner join PhoneType as pt on pn.pTypeId=pt.ptid
select * from [user]
create table [user]
(
uId int identity(1,1) primary key,
name varchar(50),
level int --1骨灰 2大虾 3菜鸟
)
insert into [user] (name,level) values('犀利哥',1)
insert into [user] (name,level) values('小月月',2)
insert into [user] (name,level) values('芙蓉姐姐',3)
select
*,
头衔='菜鸟'
from [user]
--相当于是c#中的if-else
--要求 then 后面的数据类型必须一致
select
*,
头衔=case
when [level]=1 then '菜鸟'
when [level]=2 then '老鸟'
when [level]=3 then '大师'
else '骨灰级大师'
end
from [user]
--相当于C#中的switch
select
*,
头衔=case [level]
when 1 then '菜鸟'
when 2 then '老鸟'
when 3 then '大师'
else '骨灰级大师'
end
from [user]
select * from TblScore
select
tscoreId,
tsid,
tenglish,
等级=case
when tenglish>=95 then '优'
when tenglish>=80 then '良'
when tenglish>=70 then '中'
else '差'
end
from TblScore
>=95 优
>=80 良
>=70 中
小于70 差
select
*,
是否及格=case
when tEnglish>=60 and tMath>=60 then '及格'
else '不及格'
end
from TblScore
--------------
select * from TestA
create table TestA
(
A int,
B int,
C int
)insert into TestA values(10,20,30)
insert into TestA values(20,30,10)
insert into TestA values(30,10,20)
insert into TestA values(10,20,30)select * from TestA
--表中有A B C三列,用SQL语句实现：
--当A列大于B列时选择A列否则选择B列，当B列大于C列时选择B列否则选择C列。
select
X=case
when A>B then A
else B
end,
Y=case
when B>C then B
else C
end
from TestA
--在订单表中，统计每个销售员的总销售金额，列出销售员名、总销售金额、称号（>6000金牌，>5500银牌,>4500铜牌，否则普通）
select * from MyOrders
select
销售员,
总金额=sum(销售价格*销售数量),
称号=case
when sum(销售价格*销售数量)>6000 then '金牌'
when sum(销售价格*销售数量)>5500 then '银牌'
when sum(销售价格*销售数量)>4500 then '铜牌'
else '普通'
end
from MyOrders
group by 销售员------------------------------
select * from testcreate table test
(
number varchar(10),
amount int
)
insert into test(number,amount) values('RK1',10)
insert into test(number,amount) values('RK2',20)
insert into test(number,amount) values('RK3',-30)
insert into test(number,amount) values('RK4',-10)单号 收入 支出
Rk1 10 0
Rk2 20 0
Rk3 0 30
Rk4 0 10
select
单号=number,
收入=case
when amount>=0 then amount
else 0
end,
支出=case
when amount>=0 then 0
else abs(amount)
end
from test--------------------------------------------------------------------
select *from Teamscoreselect
球队名称=teamName,
胜=case
when gameResult='胜' then 1
else 0
end,
负=case
when gameResult='负' then 1
else 0
end
from TeamScore
--------------
select
球队名称=teamName,
胜=sum(case
when gameResult='胜' then 1
else 0
end),
负=sum(case
when gameResult='负' then 1
else 0
end)
from TeamScore
group by teamName---------------------------------------------------------
select
球队名称=teamName,
胜=case
when gameResult='胜' then '胜'
else null
end,
负=case
when gameResult='负' then '负'
else null
end
from TeamScoreselect
球队名称=teamName,
胜=count(case
when gameResult='胜' then '胜'
else null
end),
负=count(case
when gameResult='负' then '负'
else null
end)
from TeamScore
group by teamName
-----------------------
select * from NBAScore
select
teamName,
第1赛季=max(case
when seasonName='第1赛季' then score
else null
end),
第2赛季=max(case
when seasonName='第2赛季' then score
else null
end),
第3赛季=max(case
when seasonName='第3赛季' then score
else null
end)
from NBAScore
group by teamName
select * from StudentScoreselect
studentId,
语文=max(case
when courseName='语文' then score
else null
end),
数学=max(case
when courseName='数学' then score
else null
end),
英语=max(case
when courseName='英语' then score
else null
end)
from StudentScore
group by studentIdselect * from MyOrders
--------------索引--------------
--1.索引的目的：提高查询效率
--2.索引分两种：
--2.1聚集索引（物理）,一个表中只能有一个聚集索引。
--2.2非聚集索引（逻辑），一个表中可以有多个非聚集索引。--3.增加索引后，会增加额外的存储空间。同时降低了增加新纪录，修改，删除的效率。
啊
吧
a
aa
b一
--------------------索引---------------------------
select c3,c4 from TestIndex1002
where c4>800 and c4<1000 order by c4 asc
create clustered index IXc4 on TestIndex1002(c4)drop index TestIndex1002.IXc4
------------------------
--3.将where条件变为c3='backuplsnparamorhinttext'，再测试select c3,c4 from TestIndex1002 where c3='backuplsnparamorhinttext'，虽然有一个聚集索引但是这个查询的where条件并没有充分利用该索引的优点，索引性能提升并不大。select c3,c4 from TestIndex1002
where c3 in('backuplsnparamorhinttext','AddresscellPhone')
order by c3 desccreate nonclustered index IXc3 on TestIndex1002(c3)
drop index TestIndex1002.IXc3
CREATE CLUSTERED INDEX [_dta_index_TestIndex1002_c_5_821577965__K3] ON [dbo].[TestIndex1002]
(
[c3] ASC
)WITH (SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF) ON [PRIMARY]
CREATE NONCLUSTERED INDEX [_dta_index_TestIndex1002_5_821577965__K4_3] ON [dbo].[TestIndex1002]
(
[c4] ASC
)
INCLUDE ( [c3]) WITH (SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF) ON [PRIMARY]
----------------------子查询-----------------------------
--查询'高二二班'的所有学生
select * from TblClass
select * from TblStudent where tSClassId=5
select * from TblStudent where tSClassId=
(select tClassId from TblClass where tClassName='高二二班')select *
from TblStudent as ts
where
exists(
select * from TblClass as tc
where ts.tSClassId=tc.tClassId and tc.tClassName='高二二班'
)
exists('fdsfsdf')
SELECT * FROM (SELECT * FROM student where sAge<30) as t
select
(select max(tenglish) from tblscore),
(select min(tenglish) from tblscore),
(select avg(tenglish) from tblscore)
SELECT
1 AS f1,
2 as f2,
(SELECT tenglish FROM tblscore) as f3
select * from TblStudent
select * from TblStudent where tsclassid in (select tclassid from TblClass)select * from student
where sClassId in
(select cId from class where cName='高一一班' or cName='高二一班')Select * from student
where exists(
select * from class where (cName='高一一班' or cName='高二二班') and class.cid=student.sclassid
)select studentId,english from score where studentId in
(select sId from student where sName='刘备' or sName = '关羽' or sName='张飞')delete from student where sId in
(select sId from student where sName='刘备' or sName = '关羽' or sName='张飞')
----------------分页查询---------------------------------
----------使用top实现分页-----------------------------------
--要分页查询，或者分页显示，首先要确定按照什么排序，然后才能确定哪些记录应该在第一页，哪些记录应该在第二页。
select * from Customers
--每页显示7条数--第1页
select top 7 * from Customers order by CustomerID asc--请查询出前2页的数据
select top (7*2) * from Customers order by CustomerID asc--第2页,思路：
--2.1先查询出（2-1）页的数据的CustomerIDselect top 7 * from Customers where CustomerID not in
(select top (7*(2-1)) CustomerID from Customers order by CustomerID asc)
order by CustomerID asc--第5页
--查询出前4也的数据的Id
select top 7 * from Customers where CustomerID not in
(select top (7*(5-1)) CustomerID from Customers order by CustomerID asc)
order by CustomerID asc
select top 7 * from Customers order by CustomerID asc
--------------使用row_number()实现分页---------------------------------------
--1.为数据排序，然后编号。
select *,Rn=row_number() over(order by CustomerID asc) from Customers
--2.根据用户要查看的每页记录条数，以及要查看第几页。确定应该查询第几条到第几条
--每页显示7条，要查看第8页
--从 (8-1)*7+1 ... 8*7select *
from (select *,Rn=row_number() over(order by CustomerID asc) from Customers) as t
where t.Rn between (8-1)*7+1 and 8*7
---作业：查询MyStudent表
select * from MyStudentselect * from TblStudent
select * from Tblclass--案例1：查询所有学生的姓名、年龄及所在班级
--TblStudent,TblClass
select
t1.tsname,
t1.tsage,
t2.tclassName
from TblStudent as t1
inner join TblClass as t2 on t1.tsclassid=t2.tclassId--案例2：查询年龄超过20岁的学生的姓名、年龄及所在班级
--TblStudent,TblClass
select
t1.tsname,
t1.tsage,
t2.tclassName
from TblStudent as t1
inner join TblClass as t2 on t1.tsclassid=t2.tclassId
where t1.tsage>20--案例3：查询学生姓名、年龄、班级及成绩
--TblStudent,TblClass,TblScore
select
t1.tsname,
t1.tsage,
t2.tclassName,
t3.tEnglish,
t3.tMath
from TblStudent as t1
inner join TblClass as t2 on t1.tsclassid=t2.tclassId
inner join TblScore as t3 on t1.tsid=t3.tsid
select * from TblScore本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。
