Help tuning a very poor SQL query

[eluser]Leon Stafford[/eluser]
[quote author="jedd" date="1245278442"]Errors ...? Go on .. share them. [/quote]

Hi jedd, thanks again.

The errors were from the JOIN ?? ON ?? line, basically the errors were as descriptive as me...

I used the ammendment for the shuffle here:

Code:

$query_string = "            
        SELECT *
        FROM kg_compounds
        WHERE NOT
        EXISTS (
            SELECT compound
            FROM kg_progress
            WHERE kg_progress.compound = kg_compounds.id AND
            (
            kg_progress.compound_progress =1 AND kg_progress.user = '$user'
            )
        
        )
        AND grade = '$level'
        
        
        
        ";

        if ($isShuffled)
        {
            $query_string .= " ORDER BY RAND()";
        }    
        $query_string .= " LIMIT 20";
            
        $query = $this->db->query($query_string);

I know I should implement the better random code as I've noticed that a lot on the forums.

And jedd, thanks for the LEFT JOIN sample, I think I should aim to migrate from the current solution to a JOIN for performance, right?