datediff的问题
SELECT *
FROM table where (datediff(ValidPeriodUnit, CheckTime, getdate())> ValidPeriod)
ValidPeriodUnit是nvarchar
ValidPeriod是int
CheckTime是datetime
这个语句就是运行不了,但是把ValidPeriodUnit换成d就可以了，但是数据库里面是动态的,可能是d,yy,mm等,我怎么样用一条sql语句实现以上功能呢，
[解决办法]
declare @ValidPeriodUnit as varchar(10)
set @ValidPeriodUnit = 'day ' -- 'year ', 'month '
declare @sql as varchar(100)
set @sql = 'SELECT * FROM table where (datediff( ' ' ' + @ValidPeriodUnit + ' ' ', CheckTime, getdate())> ValidPeriod)
exec @sql
[解决办法]
动态sql语句基本语法
1 :普通SQL语句可以用Exec执行
eg: Select * from tableName
Exec( 'select * from tableName ')
Exec sp_executesql N 'select * from tableName ' -- 请注意字符串前一定要加N
2:字段名，表名，数据库名之类作为变量时，必须用动态SQL
eg:
declare @fname varchar(20)
set @fname = 'FiledName '
Select @fname from tableName -- 错误,不会提示错误，但结果为固定值FiledName,并非所要。
Exec( 'select ' + @fname + ' from tableName ') -- 请注意 加号前后的 单引号的边上加空格
当然将字符串改成变量的形式也可
declare @fname varchar(20)
set @fname = 'FiledName ' --设置字段名
declare @s varchar(1000)
set @s = 'select ' + @fname + ' from tableName '
Exec(@s) -- 成功
exec sp_executesql @s -- 此句会报错
declare @s Nvarchar(1000) -- 注意此处改为nvarchar(1000)
set @s = 'select ' + @fname + ' from tableName '
Exec(@s) -- 成功
exec sp_executesql @s -- 此句正确
3. 输出参数
declare @num int,
@sqls nvarchar(4000)
set @sqls= 'select count(*) from tableName '
exec(@sqls)
--如何将exec执行结果放入变量中？
declare @num int,
@sqls nvarchar(4000)
set @sqls= 'select @a=count(*) from tableName '
exec sp_executesql @sqls,N '@a int output ',@num output
select @num
[解决办法]
if ValidPeriodUnit = 'day '
SELECT * FROM table where (datediff(day, CheckTime, getdate())> ValidPeriod)
else
if ValidPeriodUnit = 'year '
SELECT * FROM table where (datediff(year, CheckTime, getdate())> ValidPeriod)
else
SELECT * FROM table where (datediff(month, CheckTime, getdate())> ValidPeriod)
[解决办法]
declare @sql VARCHAR(3000)
declare @ValidPeriodUnit varchar(4)
declare @ValidPeriod varchar(100)
create table tab1(id varchar(3),checktime datetime)
select * from tab1
insert tab1
select '001 ',cast( '2007-8-28 ' as datetime)
union all
select '002 ',cast( '2007-8-2 ' as datetime)
select * from tab1
set @ValidPeriodUnit= 'day '
set @ValidPeriod=2
set @sql= '
SELECT *
FROM tab1 where (datediff( '+@ValidPeriodUnit+ ', CheckTime, getdate())> '+@ValidPeriod+ ') '
print @sql
exec(@sql)
drop table tab1
[解决办法]
SELECT *
FROM table
where
(case
when ValidPeriodUnit in ( 'year ', 'yy ', 'yyyy ') then datediff(year, CheckTime, getdate())
when ValidPeriodUnit in ( 'quarter ', 'qq ', 'q ') then datediff(quarter, CheckTime, getdate())
when ValidPeriodUnit in ( 'month ', 'mm ', 'm ') then datediff(month, CheckTime, getdate())
when ValidPeriodUnit in ( 'dayofyear ', 'dy ', 'y ') then datediff(dayofyear, CheckTime, getdate())
when ValidPeriodUnit in ( 'day ', 'dd ', 'd ') then datediff(day, CheckTime, getdate())
when ValidPeriodUnit in ( 'week ', 'wk ', 'ww ') then datediff(week, CheckTime, getdate())
when ValidPeriodUnit in ( 'hour ', 'hh ') then datediff(hour, CheckTime, getdate())
when ValidPeriodUnit in ( 'minute ', 'mi ', 'n ') then datediff(minute, CheckTime, getdate())
when ValidPeriodUnit in ( 'second ', 'ss ', 's ') then datediff(second, CheckTime, getdate())
when ValidPeriodUnit in ( 'millisecond ', 'ms ') then datediff(millisecond, CheckTime, getdate())
end)
> ValidPeriod
