sql查询中对DATEDIFF的约束

Question

我正在进行sql赋值并且在DATEDIFF上应用约束时遇到困难。 我的查询就像..

select   *,DATEDIFF('$add_date_start',submitted_date) as d1,DATEDIFF('$add_date_end',submitted_date) as d2 from table where DATEDIFF('$add_date_start',submitted_date)<=0

我也试过

select   *,DATEDIFF('$add_date_start',submitted_date) as d1,DATEDIFF('$add_date_end',submitted_date) as d2 from table where 'conditions 'HAVING d1<=0

两个查询显示0结果.. 我所要做的就是在DATEDIFF上设置约束，以便在此基础上进行选择。

当我使用mysqli_fetch_array将条件置于php中时，结果很好...，

while($row = mysqli_fetch_array($result){ if($row['d1'] <=0){ ///code } }

任何帮助都会很棒..谢谢