如何在特定的日期範圍計算在MySQL

Question

我創造了這個mysql代碼只在特定日期範圍來算，我甩的我的MySQL代碼的輸出，在這裏，它是：

SELECT COUNT(
       IF(
         DATE(q.date_emailed) BETWEEN '2014-02-01' AND '2014-02-28', 
         1, 
         0 
        ) 
     ) AS 'Feb', 
     COUNT(
        IF(
         DATE(q.date_emailed) BETWEEN '2014-03-01' AND '2014-03-31', 
         1, 
         0 
        ) 
     ) AS 'March', 
     COUNT(
        IF(
         DATE(q.date_emailed) BETWEEN '2014-01-01' AND '2014-01-31', 
         1, 
         0 
        ) 
     ) AS 'Jan' 
     FROM 
      database.quotes q 
     WHERE (DATE(q.date_emailed) BETWEEN '2014-01-01' AND '2014-03-31') 

但這輸出相同計算每個月，其中我確認二月和三月有零計數。我在這裏錯過了什麼？

Answer 1

如果要總結0和1

的計數將計算行數，總和將總結值應使用SUM，而不是COUNT。

Answer 2

COUNT()計數非空值。您可以改爲使用sum()來修復您的代碼。您也可以通過刪除if語句簡化一下：

SELECT SUM(DATE(q.date_emailed) BETWEEN '2014-02-01' AND '2014-02-28') AS Feb, 
     SUM(DATE(q.date_emailed) BETWEEN '2014-03-01' AND '2014-03-31') AS March, 
     SUM(DATE(q.date_emailed) BETWEEN '2014-01-01' AND '2014-01-31') AS Jan 
FROM database.quotes q 
WHERE DATE(q.date_emailed) BETWEEN '2014-01-01' AND '2014-03-31'; 

在MySQL中，一個布爾結果被視爲0爲「假」和1爲「真」。這非常方便，並且允許您使用sum()來計算匹配數量。

請注意，我也刪除了列名稱周圍的單引號。單引號應該用於字符串和日期常量，而不是標識符。

編輯：

你可以有這樣的查詢運行通過q.date_emailed使用索引更快。但是，我不認爲該索引將被使用，因爲date()函數。您可以通過更改邏輯來解決此問題：

SELECT SUM(DATE(q.date_emailed) BETWEEN '2014-02-01' AND '2014-02-28') AS Feb, 
     SUM(DATE(q.date_emailed) BETWEEN '2014-03-01' AND '2014-03-31') AS March, 
     SUM(DATE(q.date_emailed) BETWEEN '2014-01-01' AND '2014-01-31') AS Jan 
FROM database.quotes q 
WHERE q.date_emailed >= '2014-01-01' AND 
     q.date_emailed < '2014-04-01';