product-sku-search.php

/* paste this into your functions.php of the theme */

/ * Join posts and postmeta tables */
function product_search_join( $join ) {
    if( ! is_search() || ! is_woocommerce() ) {
        return $join;
    }
 
    global $wpdb;
 
    $join .= " LEFT JOIN {$wpdb->postmeta} wp_post_meta ON {$wpdb->posts}.ID = wp_post_meta.post_id ";
 
    return $join;
}
 
add_filter('posts_join', 'product_search_join' );
 
/* Modify the search query with posts_where*/

function product_search_where( $where ) {
    if( ! is_search() || ! is_woocommerce() ) {
        return $where;
    }
 
    global $wpdb;
 
    $where = preg_replace(
        "/\(\s*{$wpdb->posts}.post_title\s+LIKE\s*(\'[^\']+\')\s*\)/",
        "({$wpdb->posts}.post_title LIKE $1) OR (wp_post_meta.meta_key = '_sku' AND wp_post_meta.meta_value LIKE $1)", $where );
 
    return $where;
}
 
add_filter( 'posts_where', 'product_search_where' );