mysql union all 區分表名稱

背景：

最近在做報表統計，因爲查不同的訂單分佈在不同的表裏面，不同的表訂單狀態也不一樣，所以用union all 做連接的時候要區分數據是來自那張表的。

(SELECT EMAIL,sum(BESTELLWERT) as user_amount,count(*) as user_order_count,
'order' as order_table  from `order`.`order` WHERE `status` = 4 AND STAMP 
BETWEEN '2016-01-01' AND '2019-05-31' GROUP BY EMAIL HAVING SUM(BESTELLWERT) 
between 4000 and 5000)
union all
(SELECT EMAIL,sum(BESTELLWERT) as user_amount,count(*) as user_order_count,
'cdkey_order' as order_table  from `order`.`cdkey_order` WHERE `status` = 2 AND 
STAMP BETWEEN '2016-01-01' AND '2019-05-31' GROUP BY EMAIL HAVING SUM(BESTELLWERT) 
between 4000 and 5000)
union all
(SELECT EMAIL,sum(BESTELLWERT) as user_amount,count(*) as user_order_count,
'lvlguide_order' as order_table  from `order`.`lvlguide_order` WHERE `status` = 4
 AND STAMP BETWEEN '2016-01-01' AND '2019-05-31' GROUP BY EMAIL HAVING 
SUM(BESTELLWERT) between 4000 and 5000)

例子：union all 數據表來源order表則在select 字段時候增加：'order' as order_table from xxxx 那麼這個字段就可以標記來源那張表

同理：union all數據表來自cdk表，則在select時候增加:'cdkey' as order_table from xxxx

再來個例子：

（select name,uid,'user' as table_name from user）

   union all

（select name,uid,'customer' as table_name from customer）