如果记录得到这样的话，如何取小于0的值？

Question

我的查询：

 select c.location_id as id_gudang, c.location_name as nama_gudang, a.item_code as id_barang, a.item_name as nama_barang, sum(b.item_qty) as qty
    from t_inventory as a
    join t_inventory_transaction as b on a.item_id = b.item_id
    join t_site_location as c on b.whse_id = c.location_id
    group by a.item_code

来自查询的数据

Answer 1

假设您希望qty < 0想要null个值（那些不存在于该表中的值），那么您需要使用outer join代替：

select c.location_id as id_gudang, c.location_name as nama_gudang, 
       a.item_code as id_barang, a.item_name as nama_barang, 
       sum(b.item_qty) as qty
from t_inventory as a
    left join t_inventory_transaction as b on a.item_id = b.item_id
    left join t_site_location as c on b.whse_id = c.location_id
group by a.item_code

• A Visual Explanation of SQL Joins

这将返回t_inventory表中的所有记录，无论它们是否存在于其他表中。

Answer 2

如果需要，可以将sql包装到子查询中，如：

WarrantyMailer.send_warranty_email(@contact, current_user.email)

或者只使用select * from ( select c.location_id as id_gudang, c.location_name as nama_gudang, a.item_code as id_barang, a.item_name as nama_barang, sum(b.item_qty) as qty from t_inventory as a join t_inventory_transaction as b on a.item_id = b.item_id join t_site_location as c on b.whse_id = c.location_id group by a.item_code) t where qty < 0 ：

HAVING