SQL如何使用計數和分組WXY和Z

Question

假設我想要計算W，X，Y和Z中元素的數量。我不關心WXY內的具體數字，關心Z.有沒有辦法可以讓這樣的事情：

column | count 
--------------- 
WXY | 10 
    Z | 5 

代替

column | count 
--------------- 
    W | 2 
    X | 3 
    Y | 5 
    Z | 5 

Answer 1

SELECT [column] = CASE 
    WHEN [column] IN ('W','X','Y') THEN 'WXY' ELSE 'Z' END, 
    [count] = COUNT(*) 
FROM dbo.[table] 
WHERE [column] IN ('W','X','Y','Z') 
    GROUP BY CASE 
    WHEN [column] IN ('W','X','Y') THEN 'WXY' ELSE 'Z' END 
ORDER BY [column]; 

Answer 2

SQL Fiddle

select case 
    when c in ('W', 'X', 'Y') then 'XYZ' 
    else 'Z' end as c, 
    count(*) 
from t 
group by 1 

Answer 3

您可以使用公用表表達式（CTE）輕鬆完成此操作，並在嘗試獲取記錄計數之前彙總數據。

它適用於PostgreSQL和SQL Server（但如果您命名列「列」則會出現問題）。

的PostgreSQL：SQL Fiddle SQL服務器：SQL Fiddle

;with aggData as 
(
    select case 
      when c = 'Z' then 'Z' 
      else 'WXY' 
      end as col 
    from t 
) 
select col, count(*) 
from aggData 
group by col 

下面是使用CTEs with SQL Server和CTEs with PostGreSQL文檔。