動態傳遞列凝聚

Question

我需要一些幫助COALESCE。

語法：COALESCE(Col1,Col2,Col3...)這意味着每一次我將不得不寫裏面列名作爲參數的時間。

我的問題是我們可以動態傳遞的列名這個功能呢？因爲列中的列數不斷變化。

感謝， 希德

Answer 1

銥聽起來像是你有一堆列，並且要值到左側，NULL s移動到右側。

您可以通過每個值前計數的非NULL值的數目，然後使用case語句來賦值做到這一點。以下顯示了四列的代碼：

select (case when col1_n = 1 then col1 
      when col2_n = 1 then col2 
      when col3_n = 1 then col3 
      when col4_n = 1 then col4 
     end) as col1, 
     (case when col2_n = 2 then col2 
      when col3_n = 2 then col3 
      when col4_n = 2 then col4 
     end) as col2, 
     (case when col3_n = 3 then col3 
      when col4_n = 3 then col4 
     end) as col3, 
     (case when col4_n = 4 then col4 
     end) as col4 
from (select t.*, 
      (case when col1 is not null then 1 end) as col1_n, 
      ((case when col1 is not not null then 1 else 0 end) + 
       (case when col2 is not null then 1 end) 
      ) as col2_n, 
      ((case when col1 is not not null then 1 else 0 end) + 
       (case when col2 is not null then 1 else 0 end) + 
       (case when col3 is not null then 1 end) 
      ) as col3_n, 
      ((case when col1 is not not null then 1 else 0 end) + 
       (case when col2 is not null then 1 else 0 end) + 
       (case when col3 is not null then 1 else 0 end) + 
       (case when col4 is not null then 1 end) 
      ) as col4_n    
     from t 
    ) t; 

您可以在SQL小提琴（here）上看到此作品。

如果您有一個獨特的id for each，您還可以取消轉發數據，使用row_number()並重新傳輸數據。