数学函数
select ABS(-9)
select CEILING(9.00001)
select FLOOR(9.9)
select PI()
select POWER(2,3)
select SORT(9)
select SIGN(0)
select ROUND(892.35,1,7)
select ROUND(892.35,1,0)
select 1+FLOOR(LOG10(48901))
select FLOOR(RAND()*10)
字符串函?br /> select LEFT('aaaaaa',2)
select RIGHT('123456',2)
select LEN('1')
select LOWER('aaBN')
select UPPER('aaBN')
select rtrim(LTRIM('aaa'))+'**'-trim().Itrim()
select SUBSTRING('abcdefg',2,3)
select REPLACE('aba','a','ccc')
select STUFF('aaaaa',1,2,'bbbbbb')
日期旉
select GETDATE()
select YEAR(GETDATE())
select MONTH(GETDATE())
select DAY(GETDATE())
select DATEADD(mm,100,'1990-10-10')
select DATEDIFF(yy,'1988-8-8',getdate())
查询老师的年?br /> select teacher_name , DATEDIFF(yy,出生日期Qgetdate())
from dbo.teacher
转换函数
select cast('666' as int )+100
select convert(varchar(13),999)+'***'
insert into用法
1.向教师表中加入一个记录，字段的顺序与数目和表中的一?br /> insert into teacher values()
2.字段的数目与序自己指定
insert into teacher(name , sex_id) values('张三',1)
3.从select索中插入成批记录
insert into dbo.student
select teacher
from dbo.teacher
delete from dbo.student ming like'?'
update用法
1.更新一个字D?br /> Update teacher
set teacher_name='里斯'
where teacher_id=2
2.教师的基本工资上?%
Update teacjer
set 基本工资=基本工资*(1.05)
3.多字D|斎ͼ每一个用Q隔开
Update teacher
set teacher_name='李四' ,
teacjer_id = 1
where teacher_id=3
]]>
1.group by通常与集合函?avg,sum,count,max,min)配合使用
查询教师表中男女教师的h?br /> select count(*) as renshu
from dbo.teacher
group by sex_id
2.针对多字D늚分组
每个pȝ男女生的人数
select count(*) as renshu
from dbo.student
group by sex_id , p_id
3.多表查询中的分组应用
select count(*) as rs
from dbo.student xs inner join dbo.p?xi
on xs.p_id = xi.p_id
group by pd
4.对于计算字段的分l应?br /> 查询机pd生数和其他系的学生数
select count(*)
(
case
when p_id =1 then 'jsjx'
else 'qt'
end
)
from dbo.student
group by
(
case
when p_id =1 then 'jsjx'
else 'qt'
end
)
5.分组条ghaving的用?br /> pMh数在10Z上的p?br /> select count(*) as shu p_id
from dbo.student
group by p_id
having count(*) > 10
或写?br /> select *
from (
select count(*) as shu,p_id
from dbo.student
group by p_id
)linshi
where linshi.shu > 10
order by 集锦
1.对单个字D늚排序(asc升序可省?desc降序)
select teacher_id
from dbo.teacher
order by teacher_name
2.多字D|?先按W一个字D|序，如果相同再按W二个排?
select *
from dbo.teacher
order by 性别_id , p_id
3.按笔L?br /> select teacher_id
from dbo.teacher
order by teacher_name Collate Chinese_PRC_Stroke_ci_as desc
4.order by 可按l定的表辑ּ计算l果排序
按教师年龄大降序排?br /> select teacher_name
from dbo.teacher
order by DATEDIFF(yy,出生日期,getdate()) desc
本q入学的新生排在前面老生排在后面
select student_id,?br /> (
case
when ?2006 then 1
else 0
end
)
from dbo.student
order by
(
case
when ?= 2006 then 1
else 0
end
) desc
其他Q?br /> union合ƈQ?br /> 本校学生和老师的名字全部查询出来（L重复Q?br /> select teacher_name
from dbo.teacher
union
select student_name
from dbo.student
本校学生和老师的名字全部查询出来（不去掉重复）
select teacher_name
from dbo.teacher
union all
select student_name
from dbo.student
]]>
1.从一个表中检?br /> select *
from dbo.teacher
2.从一个检索结果中再检索即从时表中检?br /> select *
from (
select teacher_id , teacher_name
from dbo.teacher
) te
where te.teacher_id <4
3.从多表中索，构成W卡积(效率?
select dbo.teacher.* , pd
from dbo.teacher , dbo.p?br /> where dbo.teacher.p_id = dbo.p?p_id
4.多表的链接查询（重左表Q?br /> select *
from dbo.p?left join dbo.teacher
on dbo.p?p_id = dbo.teacher.pid
(重双)
select *
from dbo.p?right join dbo.teacher
on dbo.p?p_id = dbo.teacher.p_id
(内连?都不重)
select *
from dbo.p?/span> inner join dbo.教师
on dbo.p?/span>.p?/span>_ID=dbo.教师.p?/span>_ID inner join dbo.教师认课
on dbo.教师.教师_ID=dbo.教师认课.教师_ID
(全链?都尊?
select *
from dbo.p?all join dbo.teacher
on dbo.p?p_id = dbo.teacher.p_id
5.l被索表起别?nbsp; 注意Qv了别名就一定要用别名来引用字段
错误?br /> select dbo.teacher.teacher_id
from dbo.teacher js
正确?br /> select js.teacher_id
from dbo.teacher js
where 集锦
1.常规关系q算W?strong> >?/span> >=?/span> <?/span> <=?/span> !=?/span> <>?/span> =
select 教师_ID
from dbo.教师
where 教师_ID<>1
2.常规逻辑q算W?not , and ,or
select teacher_id
from dbo.teacher
where not (teacher_id>=1 and teacher_id<=8)
3.区间
teacher_id >=1 q且 teacher_id<=8
select teacher_id
from dbo.teacher
where teacher_id between 1 and 8
4.索null?br />
select teacher_id
from dbo.teacher
where teacher_date is null
5.关于字符的模p查?br />
(1)姓张的所有老师
select teacher_id
from dbo.teacher
where teacher_name like '?'
(2)姓张的但是名字只有两个字的老师
select teacher_id
from dbo.teacher
where teacher_name like '?'
(3)名字含有国字的所有老师
select teacher_id
from dbo.teacher
where teacher_name like '%?'
(4)老师的第一个名字在a-m之间的老师
select teacher_id
from dbo.teacher
where teacher_name like '[a-m]%'
(5)老师名字的第一个字母不在a-m之间的老师
select teacher_id
from dbo.teacher
where teacher_name like '[^a-m]%'
(6)老师的名字第一个字母是a或者b或者m的老师
select teacher_id
from dbo.teacher
where teacher_name like '[a,b,m]%'
(7)教师名字W一个字母在a到k之间或o到x之间的老师
select teacher_id
from dbo.teacher
where teacher_name like '[a-k,o-x]%'
6.关于in的用?br />
(1)枚D?br />
select *
from dbo.teacher
where teacher_id in (1,3,5)
select*
from dbo.teacher
where teacher_id not in(1,3,5)
(2)嵌套子查?br />
有课上的老师
select *
from dbo.teacher
where teahcer_id in (
select teacherid
from dbo.教师任课
)
7.exists判断子查询是否有l果Q强调有无，不关心具体是什么）
select *
from dbo.教师
where exists --存在
(
select *
from dbo.教师认课
where dbo.教师认课.教师_ID=dbo.教师.教师_ID
)
8.any其中一?br />
教师ID大于所有教师ID中Q意一个的教师Q相当于大于最ID的教师）
select *
from dbo.teahcer
where teahcer_id > any
( select teacher_id
from dbo.teacher
)
9.all全部
相当于大于最大max
select *
from dbo.teacher
where teacher_id > all(
select teacher_id
from dbo.teacher\
)
]]>
数据库拆表原则：
1.单字D中的复合字Dc解x案：向上打通或者拆成两表?br /> 2.完全依赖Q知道aq道bQ反q来׃一定。实玎ͼ同一个主题东西放在一P主题可以是一个实体、名词、概c?br /> 3.无传递依赖。将传递依赖{为直接依赖。原因：减少插入冗余Q减增删异常?br /> 4.当出C对多的时候不能横拆，一定拆成两个表Q特别的固定范围可以横拆Q签到管理）?br /> 5.多对多必有中间表?br /> 6.代码表，大量重复或枚丄可以q用代码表?br /> 7.能计的字段不要?br /> 数据定义语句DDL
create alter drop
数据控制语句DCL
grant deny revoke
数据操作语句DML
select update insert delete
SQL语句应用集锦
Select变化集锦Q?br /> 1.查询所有的字段Q效率低Q?br /> 查询所有的老师
select *
from dbo.teacher
2.字段枚D
查询老师的id 及姓名两?br /> select teacher_id , teacher_name
from dbo.teacher
3.字段取别名方法有两种使用asQas可以省略Q和不?br /> (1)select teacher_name as tN
from dbo.teacher
(2)select teacher_name = tN
from dbo.teacher
4.字段的可计算?br /> (1)单字D늚计算
教师工资?0%
select salary*0.1
from dbo.teacher
(2)把一个检索结果作为字D?br /> 本校学生和老师的比?br /> (select count(*)
from dbo.teacher)/0.1/
(select count(*)
from dbo.student)
5.索结果的前几个用top
select top 3 teacher_id
from dbo.teacher
6.取检索结果L的百分比
select top 30 percent teacher_id
from dbo.teacher
7.L重复的记?br /> select distinct sex_id
from dbo.teacher
8.在聚合统计函Cl计Z重复指定字段
select count(distinct p_id)
from dbo.teacher
9.case when then else end ?select 中的应用
从教师表中查询，性别id?的显C成P?的显C成?br /> select(
case
when sex_id = 1 then '?
when sex_id = 2 then '?
end
)
from dbo.teacher
横向查询男女?br /> select sum(
case
when sex_id = 1 then 1
else 0
end
)as 'man' ,
sum(
case
when sex_id = 2 then 1
else 0
end
)as 'wmen'
from dbo.teacher
10.可以重复列出表的字段
select *,*,*
from dbo.teacher
11.索结果放帔R
select teacher_name , '出生? , teacher_date
from dbo.teacher
]]>