MySQL comparing dates doesn't return results

Question

I need one help. I am unable to fetch value from table as per some condition using PHP and MySQL. I am explaining my table below.

db_subcat:

id    subcat_id   sub_name      from_date       to_date
------------------------------------------------------------
1       60          Ram         2016-10-25       2016-10-28
2       60          Ram                                    
3       61          Raj                                 

Here some row has no from_date and to_date value.I am explaining my query below.

$date="2016-10-23";
$sql="select * from db_subcat 
    where from_date <='".$date."' and to_date >= '".$date."' and from_date !='' and to_date !='' 
    group by subcat_id 
    union all select * from db_basic 
    where from_date ='' and to_date ='' 
    group by sucat_id";

Here My problem is i can not get value while table has no entry for (from_date ='' and to_date ='') or (from_date !='' and to_date !='') .Here i need to fetch value using the all following conditions.

1- if from_date and to_date has value and if value exist then it will match.

2- If from_date and to_date has value or blank for both condition value should fetch.

3- if table has no entry for (from_date ='' and to_date ='') or (from_date !='' and to_date !='') .

Please help me to resolve this issue.

Answer 1

If I understood you correctly, you probably need to use ISNULL and you can combine the two queries :

select * from db_subcat
where ((from_date IS NULL OR from_date ='') AND (to_date IS NULL OR to_date =''))
   OR (from_date <='".$date."' and to_date >= '".$date."') 
group by subcat_id

Note that this GROUP BY clause is invalid in all DBMS except MySQL. You shouldn't do that with a SELECT * statement, always specify the columns and each column should be either in the GROUP BY clause or with an aggregation function wrapped around it.