帮忙！写几个简单的SQL语句

convert(char(10),dateadd(day,-3,getdate()),120)



dateadd(minute,-20,getdate())



--3天前0点以前创建的记录 

select * from test

where convert(char(10),createtime,120)<convert(char(10),dateadd(day,-3,getdate()),120)



--20分钟前创建的记录

select * from test

where createtime<dateadd(minute,-20,getdate())



--查询有3门功课不及格的学生

select [name] from test

where score<60

group by [name]

having count(*)>=3



--将及格的成绩更新为1，不及格的更新为0

update test

set score=(case when score>=60 then 1 else 0 end)



/*

5.删除重复姓名的记录。如 

    1     A 

    2     B 

    3     A 

    4     A 

删除后只剩A和B两条记录。

*/

declare @t table([id] int,[name] varchar(2))

insert @t select 1,'A'

union all select 2,'B'

union all select 3,'A'

union all select 4,'A'



delete @t

where [id] not in(

                  select [id] from @t t

                  where [id]=(select min([id]) from @t where [name]=t.[name])

                 )



select * from @t





/*

id          name 

----------- ---- 

1           A

2           B

*/