如何對兩個SUM SQL求和？

Question

使用此查詢，我嘗試對兩個SUM函數的結果求和：

select 
DAY(created_at) AS day, 
SUM(if(status = '1', 1, 0)) AS result, 
SUM(if(status = '2', 1, 0)) AS noresult,
SUM(result + noresult)
from `clients` where `doctor_id` = 2 and MONTH(created_at) = MONTH(CURRENT_TIMESTAMP) group by `day`

我嘗試在這一行中這樣做：

SUM(result + noresult)

Answer 1

嘗試這個：

select 
    DAY(created_at) AS day, 
    SUM(if(status = '1', 1, 0)) AS result, 
    SUM(if(status = '2', 1, 0)) AS noresult,
    SUM(if(status in ('1', '2'), 1, 0)) 
from `clients` 
where `doctor_id` = 2 and MONTH(created_at) = MONTH(CURRENT_TIMESTAMP) 
group by `day`

Answer 2

您不能在選擇列名稱中使用別名，而必須重復代碼

select 
DAY(created_at) AS day, 
SUM(if(status = '1', 1, 0)) AS result, 
SUM(if(status = '2', 1, 0)) AS noresult,
SUM(if(status = '1', 1, 0)) + SUM(if(status = '2', 1, 0)) AS all_result

from `clients` where `doctor_id` = 2 and MONTH(created_at) = MONTH(CURRENT_TIMESTAMP) group by `day`

您必須重復代碼，因為不同的SQL子句是按照特定的順序處理的（首先是從那里開始，然后是select和group by ....等。），因此在select解析時別名不能用於sql引擎

Answer 3

正如其他幾個人所述，您不能在select語句中使用別名。 但是，為了使其更整潔，您可以合並兩個條件，而不是對兩個SUM字段求和。

select 
DAY(created_at) AS day, 
SUM(if(status = '1', 1, 0)) AS result, 
SUM(if(status = '2', 1, 0)) AS noresult,
SUM(if(status = '1' OR status = '2', 1, 0)) AS newcolumn
from `clients` where `doctor_id` = 2 and MONTH(created_at) = MONTH(CURRENT_TIMESTAMP) group by `day`