在一個查詢中獲取不同子句的計數

Question

獲得計數的效率還是比我在下面做的更好？

select 
    i.org_id, 
    o.Org_Name_1, 
    count(*) as 'Total Users', 
    SUM(CASE WHEN i.email is NULL THEN 1 ELSE 0 END) as 'No Email' 
from 
    individu i, 
    organiz o 
where 
    i.org_id = o.org_id 
group by 
    i.org_id, o.Org_Name_1 
order by 
    count(*) desc 

Answer 1

SUM(CASE WHEN i.email is NULL THEN 1 ELSE 0 END) as 'No Email' 

可以與因更換...從MSDN Count(Transact SQL)

COUNT（ALL表達）引評估表達的一組中的每一行，並返回非空值的數量。

當一個表達式放在COUNT語句的括號中時，它將只評估和計算該字段中的非空值。因此，如果您使用Count（*） - Count（field），您將獲得所有空字段的總數。

COUNT(*) - COUNT(i.email) AS 'No Email' 

您的查詢會再看看這樣的：

SELECT 
    i.org_id, 
    o.Org_Name_1, 
    COUNT(*) AS 'Total Users', 
    COUNT(*) - COUNT(i.email) AS 'No Email' 
FROM 
    individu i, 
    organiz o 
WHERE 
    i.org_id = o.org_id 
GROUP BY 
    i.org_id, o.Org_Name_1 
ORDER BY 
    COUNT(*) DESC