Question

To create a table, I am retrieving the data with the following query:

SELECT cId,cProductId,cDate,cInfo FROM tProduct ORDER BY cProductId ASC,cDate ASC;

Naturally I simplified the query a lot, but you get the notably, there might be many record for a same product, and the only one that interest me in the newest, thus how I order my query: I only store the information for the last row I encounter in my while loop.

while (($row = $result->fetch()) !== FALSE)
{
      if(!empty($row[0])){
          if(($table_row[1]!=$row[1])&&(!empty($table_row[0]))){
              //Display the last row saved
          }
          $table_row= array($row[0],$row[1],$row[2],$row[3]);
      }
}

Now I want to implement some sorting options for the html table which is generated. I’ll store the sorting information in a session variable. Amongst the sorting option, I want to be able to sort by date. How can I be sure to retrieve only the newest row for each product while ordering my query by date?

Answer 1

You didn’t include FROM clause in your query. However, assuming you want the newest row per product ID, you can do something like this:

SELECT cId,cProductId,cDate,cInfo
FROM tProduct t1
WHERE cDate = (SELECT max(cDate) FROM tProduct t2 where t1.cProductID = t2.cProductId)
ORDER BY cProductId ASC,cDate ASC;