如何在MySQL中特定日期范围内计数

Question

我创建了此mysql代码以仅在特定日期范围内进行计数，我转储了mysql代码的输出，此处为：

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')

但这每月输出相同的计数，其中我确认2月和3月计数为零。 我在这里想念什么？

Answer 1

COUNT()计算非空值。 您可以改用sum()来修复代码。 您也可以通过删除if语句来简化它：

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，布尔结果对于“ false”被视为0对于“ true”被视为1 。 这是一个极大的方便，它允许您使用sum()来计算匹配数。

请注意，我还删除了列名周围的单引号。 单引号应用于字符串和日期常量，而不用于标识符。

编辑：

通过使用q.date_emailed上的索引，可以使此查询运行更快。 但是，我不认为由于date()函数会使用索引。 您可以通过更改逻辑来解决此问题：

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';

Answer 2

如果要累加0和1，则应使用SUM而不是COUNT。

COUNT将对行数进行计数，SUM将对这些值求和。