说的不够详细...我再来一次!!在线等~~~~~~~~

declare @v varchar(10)

select @v = '40'

select * from (

select 1 id,'字符串比较40<5' sm,case when @v>  '5' then @v else 5   end as v union

select 2,'数字比较40>5'        ,case when @v>   5  then @v else 5   end      union

select 3,'字符串比较40>300'    ,case when @v>'300' then @v else 300 end      union

select 4,'数字比较40 <300'     ,case when @v> 300  then @v else 300 end 

) a order by id

/*

id          sm               v           

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

1           字符串比较40<5        5

2           数字比较40>5         40

3           字符串比较40>300      40

4           数字比较40 <300      300

*/

declare @v varchar(10)

select @v = '40'

select case when @v>5 then @v else 5 end 

union select case when @v> 300 then @v else 300 end 

/*

----------- 

40

300

*/

select * from tb_register a where 

exists (select 1 from tb_content where a.rid = rid 

and pname ='面积' and ptype >=100)--sql会自动类型转换。

and 

exists (select 1 from tb_content where a.rid = rid 

and pname ='朝向' and ptype = '南')

select * from tb_register a where 

exists (select 1 from tb_content where a.rid = rid 

and (pname ='面积' and ptype >=100)--sql会自动类型转换。

and (pname ='朝向' and ptype = '南'))