SQL语句有关问题，如何查结果都一样

SQL语句问题，怎么查结果都一样
select *
from DQ_Rp_Plan_Houseitem
where datediff(dd,cast('2012-04-12' as datetime),cast('2012-04-15' as datetime)) between 1 and 5

和


select *
from DQ_Rp_Plan_Houseitem
where datediff(dd,cast('2012-04-12' as datetime),cast('2012-04-19' as datetime)) between 1 and 5

和

select *
from DQ_Rp_Plan_Houseitem
where datediff(dd,cast('2012-04-12' as datetime),cast('2012-04-15' as datetime)) between 1 and 10


怎么查结果都一样 结果都是数据表里的全部数据 没有 按指定时间显示

哪里的问题？

数据库的 日期字段 为字符串型的 vchar



[解决办法]

SQL code

select *from DQ_Rp_Plan_Houseitemwhere datediff(dd,cast('2012-04-12' as datetime),cast('2012-04-15' as datetime)) between 1 and 5--datediff(dd,cast('2012-04-12' as datetime),cast('2012-04-15' as datetime))=3,3在1和5之间，条件为真，但会所有结果和select *from DQ_Rp_Plan_Houseitemwhere datediff(dd,cast('2012-04-12' as datetime),cast('2012-04-19' as datetime)) between 1 and 5 --datediff(dd,cast('2012-04-12' as datetime),cast('2012-04-19' as datetime))=7，不在1和5之间，返回空集和select *from DQ_Rp_Plan_Houseitemwhere datediff(dd,cast('2012-04-12' as datetime),cast('2012-04-15' as datetime)) between 1 and 10--datediff(dd,cast('2012-04-12' as datetime),cast('2012-04-15' as datetime))=3，条件成立，返回所有结果
[解决办法]
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如果用
SQL code



select *
from DQ_Rp_Plan_Houseitem
where datediff(dd,cast('2012-04-12' as datetime),getdate()) between 1 and 5




不提示错误 但会没有结果

[解决办法]
SQL code
select *from DQ_Rp_Plan_Houseitemwhere datediff(dd,cast('2012-04-12' as datetime),getdate()) between 1 and 5--datediff(dd,cast('2012-04-12' as datetime),getdate())值为17--不在1到5的范围内，条件不成立，所以表里面的内容查不出来
[解决办法]
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select *
from DQ_Rp_Plan_Houseitem
where datediff(dd,cast('2012-04-12' as datetime),cast('2012-04-15' as datetime)) between 1 and 5

和


select *
from DQ_Rp_Plan_Houseitem
where datediff(dd,c……