使用php循环加速大sql查询

Question

我试图让这些SQL查询更快。我已尝试过索引等等，但我不确定如何让它更快。欢迎任何提示或要点。它是旧程序员制作的旧代码，试图修复它。它是一个MySQL数据库。

我有两个表格：

wp_l（550 000并且每天都在增长）和wp_lP（540 000,000并且不断增长）

结构：

wp_l:
id - int(9)
epost - (varchar255)
userID - int(9)
date - timestamp
and a few more fields containing info thats not used in this case.

wp_lP:
id - int(9)
lID - int(9) [is the id it belongs to in wp_l, nothing is done in "mysql" to make them relate]
pID - int(9)
quantity - int(9)

我的PHP代码：

<?php
    $years = $wpdb->get_results($wpdb->prepare("SELECT YEAR(date) AS year FROM wp_l WHERE userID = %d OR epost = %s GROUP BY year DESC", $current_user->ID, $current_user->user_email));
    if(count($years) == 0) {
        //No result
    } else {
    foreach ( $years as $year ) {

    echo $year->year;

        $myOrders2 = $wpdb->get_results($wpdb->prepare("SELECT * FROM wp_l WHERE YEAR(date) = %s AND (userID = %d OR epost = %s) ORDER by id DESC", $year->year, $current_user->ID, $current_user->user_email), ARRAY_N);
        for($i=0; $i<count($myOrders2); $i++) {

        $ar = substr($myOrders2[$i][3], 0, 4);

            $ordersProducts2[$i] = $wpdb->get_results($wpdb->prepare("SELECT * FROM wp_lP WHERE lID = %d ORDER by id", $myOrders2[$i][0]), ARRAY_N);

            for($j=0; $j<count($ordersProducts2[$i]); $j++) {
                $loopProductID = $ordersProducts2[$i][$j][2];
                $quantity = $ordersProducts2[$i][$j][3];
                $tid = $myOrders2[$i][3];
                include(locate_template('loopfile.php'));
            } 
        } 
    }
    }
?>

提前致谢！