There are several issues in your function. Do not use backticks in the sql. Don't put quotes around field names. You use `get_results` with `LIMIT 1` when you only need the value from a single column in a single row. And you use `$meme_sku` instead of... `$post_sku` ? Just guessing with this example, it might work... function update_custom_post_meta_data() { global $wpdb; $args = array( 'posts_per_page' => -1, 'post_type' => 'product', 'suppress_filters' => true, 'meta_key' => '_sku' ); $posts_array = get_posts( $args ); $customTable = $wpdb->prefix.'custom_table'; foreach($posts_array as $post) { $post_id = $post->ID; $post_sku = get_post_meta($post_id,'_sku',true); $result = $wpdb->get_var( "SELECT custom_column1 FROM $customTable WHERE custom_key_id = $post_sku"); if ( $result != NULL ) { update_post_meta($post_id, 'custom_meta_key', $result); } } }