inventory_held_by_customer 函數會傳回租借指定庫存項目的客戶的 customer_id。

參數

傳回值

此函數會傳回目前租借該項目的客戶的 customer_id，如果該項目有庫存則傳回 NULL。

使用範例

mysql> SELECT inventory_held_by_customer(8);
+-------------------------------+
| inventory_held_by_customer(8) |
+-------------------------------+
|                          NULL |
+-------------------------------+
1 row in set (0.00 sec)

mysql> SELECT inventory_held_by_customer(9);
+-------------------------------+
| inventory_held_by_customer(9) |
+-------------------------------+
|                           366 |
+-------------------------------+
1 row in set (0.00 sec)