sql 語句 select

--select * from Tbclass
--select clsName,clsNumber,clsTeacher into TbClassBak from Tbclass
--只能網不存在的表中存數據
--insert into 舊錶名 (字段列表) select 字段列表 for 舊錶名
--stlect * from biaoming ziduan in()
insert  into Tbstudent values('天明','154830843',0,'安陽',60,'13290826437',1)
insert  into Tbstudent values('天華','164855283',0,'安陽',20,'13290826437',1)
insert  into Tbstudent values('天山','172705183',0,'安陽',16,'13290826437',1)
select * from Tbstudent
--給列其別名
select * from  Tbstudent

select stuName as '姓名',
stuNumber '學號',
性別 = stuGender
from Tbstudent
select * from Tbstudent where stuGender !=1
select top(5)* from Tbstudent-- where stuClassId in(1,3,5)
--top 查詢前幾條
select top 30 percent * from Tbstudent
--distinct 去除重複記錄 
select distinct stuAddress from Tbstudent
-- %__ %,%__,__%,   [ , , ]% 要麼三選一名字開頭 每一個必須是單個字符
select * from Tbstudent where stuName like '小%'
select * from Tbstudent where stuName  like '小%' or stuName like 'xia%'
--查詢15-18級的學生的所有信息  ^必須放在[]裏面
select * from Tbstudent where stuNumber like '1[2-6]%'
--不是
select * from Tbstudent where stuNumber not like '18%'
select * from Tbstudent where stuName  not like '%xia%'
--count  計數  sum max avg min   len求字符串的 長度 聚合函數
select count (*) from Tbstudent
--判斷字段爲NULL 要用is
--SELECT * FROM Tbstudent where stuName  is null
alter table Tbstudent add stuMath int 
alter table Tbstudent add stuEnglish int 
select * from Tbstudent where stuMath is null
select stuName,stuMath,stuEnglish  from Tbstudent
select stuName,stuNumber,stuMath+10 as '數學'  from Tbstudent
--替換 轉換類型 一個字段只能是一個數據類型
select stuName,stuNumber, ISNULL(CAST(stuMath as varchar(4)),'缺考') ,
ISNULL(CAST (stuEnglish as varchar(4)),'缺考') from Tbstudent