Remove CURRENT_TIMESTAMP default on the stock table (#2590)

* Remove the default timestamp value which requires mysql 5.6.5

* Change REPLACE INTO with INSERT INTO .. ON DUPLICATE KEY UPDATE

This will allow us to set the timestamp value on first insert only.

Author: mikejolley

src/Installer.php

@@ -58,8 +58,8 @@ public function maybe_create_tables() {
 				`order_id` bigint(20) NOT NULL,
 				`product_id` bigint(20) NOT NULL,
 				`stock_quantity` double NOT NULL DEFAULT 0,
-				`timestamp` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
-				`expires` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
+				`timestamp` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
+				`expires` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
 				PRIMARY KEY  (`order_id`, `product_id`)
 			) $collate;
 			"

src/StoreApi/Utilities/ReserveStock.php

@@ -162,9 +162,10 @@ private function reserve_stock_for_product( $product_id, $stock_quantity, \WC_Or
 		$result = $wpdb->query(
 			$wpdb->prepare(
 				"
-				REPLACE INTO {$wpdb->wc_reserved_stock} ( order_id, product_id, stock_quantity, expires )
-				SELECT %d, %d, %d, ( NOW() + INTERVAL %d MINUTE ) from DUAL
+				INSERT INTO {$wpdb->wc_reserved_stock} ( `order_id`, `product_id`, `stock_quantity`, `timestamp`, `expires` )
+				SELECT %d, %d, %d, NOW(), ( NOW() + INTERVAL %d MINUTE ) FROM DUAL
 				WHERE ( $query_for_stock FOR UPDATE ) - ( $query_for_reserved_stock FOR UPDATE ) >= %d
+				ON DUPLICATE KEY UPDATE `expires` = VALUES( `expires` )
 				",
 				$order->get_id(),
 				$product_id,