How to directly update WooCommerce product stock quantity by its sku

A have a ton of variable products. I’m using cron to run the script every X minutes for fetching stock level from an external source. If I use wc_get_product_id_by_sku and update_post_meta it takes too long so I’m trying to find the way to use a custom prepared query. If I know product_id query would be like that:

$conn->prepare( "UPDATE wp_postmeta SET meta_value=? WHERE post_id=? AND meta_key=`_stock`" );

But I only know a product SKU. So how to modify this query to update _stock based on a product SKU?

post_id	meta_key	meta_value
10	_sku	ABCD
10	_stock	25

Answer

$wpdb and JOIN works too slow, so the fastest way is to use four separate prepared queries:

$conn = mysqli_init();
mysqli_real_connect( $conn, DB_HOST, DB_USER, DB_PASSWORD, DB_NAME );

// Get product ID by SKU
$stmt1 = $conn->prepare( "SELECT post_id FROM {$wpdb->prefix}postmeta WHERE meta_key = '_sku' AND meta_value = ?");

// Update stock level on postmeta table
$stmt2 = $conn->prepare( "UPDATE {$wpdb->prefix}postmeta SET meta_value = ? WHERE meta_key = '_stock' AND post_id = ?");

// Update stock data on wc_product_meta_lookup table
$stmt3 = $conn->prepare( "UPDATE {$wpdb->prefix}wc_product_meta_lookup SET stock_quantity = ?, stock_status = ? WHERE product_id = ?");

// Update stock status on postmeta table
$stmt4 = $conn->prepare( "UPDATE {$wpdb->prefix}postmeta SET meta_value = ? WHERE meta_key = '_stock_status' AND post_id = ?");

foreach ( $products as $product ) {
    $qty        = $product['ON_HAND'];
    $sku        = $product['PRODUCT_SKU'];
    $status     = $qty ? 'instock' : 'onbackorder';

    // Get product ID by SKU
    $stmt1->bind_param( "s", $sku );
    $stmt1->execute();

    $res = $stmt1->get_result();
            
    while ( $row = $res->fetch_assoc() ) {

        $id = $row['post_id'];

        // Update stock level on postmeta table
        $stmt2->bind_param( "dd", $qty, $id );
        $stmt2->execute();

        // Update stock data on wc_product_meta_lookup table
        $stmt3->bind_param( "dsd", $qty, $status, $id );
        $stmt3->execute();

        // Update stock status on postmeta table
        $stmt4->bind_param( "sd", $status, $id );
        $stmt4->execute();
   }
}