Buying Sum Custom Field For Current User Only - Wordpress

What I'm trying to do is query and sum a custom field in Wordpress for the current logged in user.

I have a website for my writing company that lets writers log in and claim work that they want to do. For each assignment, there is a field called "Word Count" where I input the word count for the article that needs to be done. To calculate how much each writer is owed for an assignment, I use the word count field (with the meta key "assignment_word_count" ) and multiply it by a flat rate that each writer is paid per word.

So far the closest script I've put together that does what I want it do is an SQL script. Unfortunately, it sums ALL of the word count fields instead of just the ones that belong to the current user. If I try to add anything to the code to limit it to the current user, the total drops to zero.

<?php
$now = current_time('mysql');
                $sql = "SELECT ";
                $sql .= "meta_value FROM $wpdb->posts AS posts, $wpdb->postmeta AS postmeta ";
                $sql .= "WHERE posts.ID = postmeta.post_id AND postmeta.meta_key =     'assignment_word_count' ";
                $sql .= "AND posts.post_status = 'paid' ";
                $sql .= "AND posts.post_date < '$now' ";
                $sql .= "AND postmeta.meta_value != '' ";
                $results = array(); $values = array();
                $results = $wpdb->get_results($sql);
                $totalpay = 0;
                if (!empty($results)){
                    foreach ($results as $result) {
                        $totalpay += $result->meta_value;
                    }
                }
                echo  'Total Paid: $' . $totalpay * money_format('0.0040=(#10.2n', $number);
?>

PHP:

There's also another script I found that is supposed to do exactly what I'm looking for, but it tells me that the implode line is an invalid argument.

 <?php
        //get current user
        global $current_user;
        get_currentuserinfo();
        // build query of ids by user
        $userPosts = get_posts(array('author' => $current_user->ID, 'post_type'=> 'assignments')); //change this

        // loop to create array of ids by user
        foreach ($userPosts as $post) {
            setup_postdata($post);
            $ids[] = get_the_ID();
        }
        $idList = implode(",", $ids); //tun this crap into a list

        $meta_key = 'assignment_word_count';//set this to your custom field meta key
        $totalpay = $wpdb->get_col($wpdb->prepare("
                                          SELECT meta_value
                                          FROM $wpdb->postmeta
                                          WHERE meta_key = %s
                                          AND post_id in (" . $idList . ")", $meta_key));
        echo 'Total pay: $ ' . array_sum( $totalpay);   ?>

PHP:

I've been working on this for days and I really need to get this done soon. Can someone help me? Either script will work fine. I don't care which one as long as it works. I need a script that can sum the word count field for the "Paid" post status for only the current user.

First person to give me a working solution for the cheapest rate gets the job.

 

I do not see where you are specifying in the query that you only want the sum of one user. You should add

$sql .= "WHERE posts.ID = postmeta.post_id AND postmeta.meta_key = 'assignment_word_count' AND postmeta.user_id";

from the way it looks to me

 

Ok try AND postmeta.post_author instead

 

No luck. It still makes the total drop to zero for some reason. What about that second script I posted? That one's suppose to do exactly what I'm looking for, according to the person who originally posted it. I get an error saying the implode part is an invalid argument, though.