Question

I have the following query which is working:

$query = "SELECT 
   a.student_name, 
   city, 
   state, 
   request_date, 
   lat, 
   lng, 
   (3959 * acos( 
      cos( radians('".mysql_real_escape_string($center_lat)."') ) 
      * cos( radians( lat ) ) 
      * cos( radians( lng ) - radians('".mysql_real_escape_string($center_lng)."') ) 
      + sin( radians('".mysql_real_escape_string($center_lat)."') ) 
      * sin( radians( lat ) ) 
      ) 
   ) AS distance 
   FROM lesson_requests a
   INNER JOIN (
      SELECT student_name, MAX(request_date) AS MaxRequestDate
      FROM lesson_requests
      WHERE ( 
        3959 * acos( 
          cos( radians('".mysql_real_escape_string($center_lat)."') ) 
          * cos( radians( lat ) ) 
          * cos( radians( lng ) 
          - radians('".mysql_real_escape_string($center_lng)."') ) 
          + sin( radians('".mysql_real_escape_string($center_lat)."') ) 
          * sin( radians( lat ) ) ) 
      ) < ".mysql_real_escape_string($radius)." 
      GROUP BY student_name
   ) b
   ON a.student_name = b.student_name
   AND a.request_date = b.MaxRequestDate
   HAVING distance < ".mysql_real_escape_string($radius)." 
   ORDER BY distance 
   LIMIT 0 , 10";

What i am trying to do is join in another table to the query called ‘vendor’. That table has a value called ‘user_purchased’ and as one of the filters at the end of the complete query I have to make sure that ‘user_purchased’ from the table named ‘vendor’ does not contain the words ‘abc_company’. using MATCH like this

...AND NOT MATCH(user_purchased) AGAINST ('abc_company')

Could someone help me with the join of this additional table?

Thanks in advance!

Answer 1

There’s a lot going on there…

First, HAVING should only be used with a corresponding GROUP BY. Your GROUP BY applies to the sub query (think of it as a table). I think you want a WHERE clause there.

The self-join (*lesson_requests INNER JOIN (SELECT stuff from lesson_requests*) is kinda confusing too though I can see what you’re trying to do (namely, get the record per student with the max request date).

Finally, a varchar like “name” usually makes for a bad Primary Key. Consider creating some sort of integer student ID surrogate key and using that instead.

Regardless, I think you want something like:

SELECT student_name, 
       city, 
       state, 
       request_date, 
       lat, 
       lng, 
       <<DISTANCE COLUMN>> AS distance, 
       vendor.user_purchased
FROM lesson_requests 
INNER JOIN 
   (
    SELECT student_id, MAX(request_date) AS max_request_date
    FROM lesson_requests
    WHERE <<COMPLEX CONDITION>>
    GROUP BY student_name
   ) AS recent_student_lesson_request
   ON  lesson_requests.student_name = recent_student_lesson_request.student_name
       AND lesson_requests.request_date = recent_student_lesson_request.max_request_date
LEFT JOIN vendor ON v.user_purchased = lesson_requests.student_name
WHERE vendor.user_purchased <> 'abs_company'
    AND distance < BLAH;

This joins in the vendor table as an OPTIONAL table and assumes that user_purchased in the vendor table corresponds to the student_name. If that assumption doesn’t apply, you need to figure out how vendor and lesson_requests is related and do the join using those columns.

This will still print out a record if a given student_name never appears in the vendor table (because, obviously a student that IS NOT a vendor CAN NOT be the vendor ‘abc_company’)