Question

The following code is used in a query for fetching records. It uses the electors.ID to find the corresponding voting_intention.elector from a second table.

$criteria = "FROM voting_intention,electors WHERE voting_intention.elector = electors.ID AND voting_intention.pledge IN ('C','P') AND electors.postal_vote = 1 AND electors.telephone > 0"

The problem is that some electors will have more than one pledge in the voting_intentions table.

I need it to match only on the latest voting_intention.pledge based on the field votin_intention.date for each elector.

What is the simplest way of implementing that.

The rest of the code:

function get_elector_phone($criteria){
    $the_elector = mysql_query("SELECT * $criteria ORDER BY electors.ID ASC"); while($row = mysql_fetch_array($the_elector)) { 
    echo $row['ID'].','; }  
}

Answer 1

You could use a sub-select with the MAX() function. Add the following into your WHERE clause.

AND voting_intention.date = (select MAX(date) 
                         from voting_intention vote2 
                         where voting_intention.elector = vote2.elector)

Here is a SQLFiddle of the results.