如何在其他表中檢查聯接值是否為空和查找

Question

如果accomm_bk和type_bk的連接值為Null，則如何在表中查找值表示lookup_accomm_bk和lookup_type_bk 。

任何幫助將不勝感激。

select accomm_bk,type_bk
from 
staging.contract a 
left join dim.accomm_dim b on (a.accomm_id)= b.accomm_hash
left join dim.type_dim c on (a.accomm_id)= c.type_hash

如果結果為null，那么如何查找staging.contract a有桌子lookup_accomm_bk列accomm_bk和lookup_type_bk列type_bk和獲取值。

例

accomm_bk | type_bk
--------------------
NULL      | NULL

Answer 1

如果Result為NULL，則如何查找staging。使用表lookup_accomm_bk的accomm_bk列和表lookup_type_bk的type_bk列來契約a並獲取值。

您將需要在查詢中再添加兩個LEFT JOIN ，以將contract表鏈接到表lookup_accomm_bk和lookup_type_bk 。

如果在accomm_dim和type_dim找不到查找的值，則使用COALESCE函數顯示查找的值。

這是查詢的框架（您需要為其他LEFT JOIN定義適當的ON子句）：

select 
    COALESCE(b.accomm_bk, lb.accomm_bk),
    COALESCE(c.type_bk, lc.type_bk)
from 
    staging.contract a 
    left join dim.accomm_dim b on (a.accomm_id)= b.accomm_hash
    left join dim.type_dim c on (a.accomm_id)= c.type_hash
    left join dim.lookup_accomm_bk lb on ...
    left join dim.lookup_type_bk lc on ...