GROUP BY

Question

我有以下方式的數據....

 
ColumnA ColumnB 
7675 22838 
7675 24907 
7675 NULL 

我想在下面的方式，結果.....

 
ColumnA ColumnB 
7675 2 (need total count for Not Null value) 
7675 0 (need count 0 for NULL value) 

Answer 1

select columnA, 
     count(columnB) as non_null_count, 
     sum(columnB is null) as null_count 
from your_table 
group by ColumnA 

Answer 2

SELECT ColumnA, COUNT(ColumnB) ColumnB 
FROM YourTable 
GROUP BY ColumnA 
UNION ALL 
SELECT ColumnA, 0 
FROM YourTable 
WHERE ColumnB IS NULL 
GROUP BY ColumnA 

Answer 3

你可以很容易地做一個計數和總和，這可能會更快，如果有很多的行，而不是選擇所有的行兩次與UNION

SELECT columna, columnb, SUM(mycount) 
FROM 
( SELECT *, COUNT(columnb) as mycount 
    FROM test 
    GROUP BY columnb 
)t 
GROUP BY mycount 
ORDER BY CASE WHEN mycount = 0 THEN 1 ELSE 2 END DESC; 

Fiddle Demo

Answer 4

你可以引入一個計算列表示ColumnB是否爲空或不與ColumnA一起使用它作爲一個分組標準：

SELECT 
    t.ColumnA, 
    ColumnB = COUNT(t.ColumnB) 
FROM 
    dbo.YourTable AS t 
CROSS APPLY 
    (SELECT CASE WHEN t.ColumnB IS NULL THEN 1 ELSE 0 END) AS x (SubGroup) 
GROUP BY 
    t.ColumnA, 
    x.SubGroup 
ORDER BY 
    t.ColumnA, 
    x.SubGroup 
; 

的COUNT(t.ColumnB)表達式將始終爲NULL的空子組，並且對於相應的非空子組，它將返回非空條目的數量。