随机函数
select rand()
declare @age int
set @age = rand()*100
select @age
数据类型转换
declare @birthday datatime
set @birthday = getdate()
select convert (varchar,@birthday)
时间函数
select getdate()
select convert(varchar(4),Year(getdate()))
select dateadd(dd,2(getdate())) 日
select dateadd(mm,2(getdate())) 月
select dateadd(yy,2(getdate())) 年
select datediff(day,'2005-3-4',(getdate())) 计算给定日期和现在日期相差天数
流程控制语句
判断语句
if 条件…… else……
case 条件 when 5 then ……
when 6 then……
else …… end
case when @scroe<60 then ....
循环 while (条件）
begin
……
end
实例：
declare @time int, @a varchar(100) set @time=0 set @a='*' while (@time<20) begin print @a set @a+='*' set @time+=1 end
动态构造SQL语句
declare @tableName nvarchar(20)
set @tableName='T'+convert(varchar(4),Year(getdate()))+'年'+convert(varchar(2),Month(getdate()))+'月'+convert(varchar(2),day(getdate()))+'日'
execute (' create table ' +@tablename+' (studentid int, studentName nvarchar(10)) ')
过滤数据
使用比较操作符 = > < >= <= <>
使用字符比较符 like
% 0个或多个字符串
—任何单个的字符
【】在指定区域或集合内的任何单个字符
【^】不在指定区域或集合内的任何单个字符
select * from tsudent where sname like '高%'
select * from tstudent where sname like '_[明,宇]_'
查询未知的值
select * from tstudent where class is null --查找班级为空的学生
select * from tstudent where class is not null --查找班级不为空的学生
格式化结果集
排序
asc 升序 desc降序
实例： select * from tscore order by mark desc
去重 distinct
select distinct class from tstudent
多表查询
内连接 select a.*,b.* from student a join score b on a.studentid=b.studentid
左右连接 select a.*,b.* from student a left （right）join score b on a.studentid=b.studentid
数据分组和汇总
TOP n 列出前n行记录
select top 5 * from tstudent order by Birthday
使用聚集函数
count(*) count(列） sum min max avg
select count(*) from tstudent
统计表中class列不为空的记录数量 select count(class) from tstudent
select avg(mark) from tscore where subjectid=1
group by 使用例子
select Class,count(*) from tstudent group by Class
select sname,avg(mark) from tscore a join tstudent b on a.studentid=b.studentid group by sname having avg(mark)>77 --having 相当于条件
多列汇总
select subjectname,class,sum(mark) from tstudent a join tscore b on a.studentid=b.studentid join tsubject c on b.subjectid=c.subjectid group by subjectname,class with rollup -- 联合使用group by 子句和操作符rollup，将两列的详细信息和分组汇总
联合使用cube，将对列出subject那么，class两列进行汇总
select subjectname,class,sum(mark) from tstudent a join tscore b on a.studentid=b.studentid join tsubject c on b.subjectid=c.subjectid group by subjectname,class with cube
查找网络管理课程的学生成绩
select studentid,subjectname, mark from tscore a join tsubject b on a.subjectid=b.subjectid where subjectname='网络管理'
另一种写法
select studentid, sname from tstudent where studentid in (select studentid from
(select studentid,avg(mark) trt from tscore group by studentid having avg(mark)<60) as t1)
数据增删改查
插入
insert tstudent values('0000001902','hanligang','男','1414121548554236565','1984-5-12','[email protected]','网络班',getdate())
insert tstudent (studentid,sex,name) values ('454514545','man','jkjdkf') -- 插入部分数据
insert tnetwork select * from tstudent where class='网络班' --将查询的数据插入现有表中
select studentid,sname,sex,email into TDev from tstudent where calss='网络班' --将查询的记录创建新的表
删除
delete tstudent where studentid='24234234'
delete tstudent where birthday <'1982-1-1'
delete tstudent where studentid in (select distinct studentid from tscore where mark<60)
delete tstudent where studentid in (select distinct a.tstudentid from tstudent a join tscore b on a.studentid=b.studentid where mark<60)
等价于