Добавил свое поле. Как сделать проверку на уникальность? - [VM1] Управление товарами, атрибутами, типами, ценами

#1062 - Duplicate entry '' for key 'product_sku_dx'
ALTER TABLE  `jos_vm_product` ADD UNIQUE (
`product_sku_dx`
);

/administrator/components/com_virtuemart/html/product.product_list.php

$search_sql = " (#__{vm}_product.product_name LIKE '%$keyword%' OR \n";
$search_sql .= "#__{vm}_product.product_sku LIKE '%$keyword%' OR \n";
$search_sql .= "#__{vm}_product.product_s_desc LIKE '%$keyword%' OR \n";
$search_sql .= "#__{vm}_product.product_desc LIKE '%$keyword%'";
$search_sql .= ") \n";

$search_sql = " (#__{vm}_product.product_name LIKE '%$keyword%' OR \n";
$search_sql .= "#__{vm}_product.product_sku LIKE '%$keyword%' OR \n";
/*##my17052011224824 { Added to use my field
It was:
It became:*/
$search_sql .= "#__{vm}_product.product_sku2 LIKE '%$keyword%' OR \n";
/*##my17052011224824 } */
$search_sql .= "#__{vm}_product.product_s_desc LIKE '%$keyword%' OR \n";
$search_sql .= "#__{vm}_product.product_desc LIKE '%$keyword%'";
$search_sql .= ") \n";