Question

我在mySQL上有以下sqlfiddle schema和查询。

基本上我正在尝试在每个日期间隔内获取count个项目。

目前所有内容都按预期工作，但我发现我必须使用多个MySQL查询才能检索所需的数据。

有没有办法将这些查询组合成任意数量的日期间隔？因此，在示例中，我有2个不同的查询来查询2个不同的日期间隔。我想知道是否可以在单个查询中查询3个或4个或更多个日期间隔？

Answer 1

您使用conditional sum作为

select 
sum( 
  case when joined > '2014-01-01' and joined < '2014-06-30'
  then 1 else 0 end
) as count1,
sum( 
  case when joined > '2014-07-01' and joined < '2014-12-31'
  then 1 else 0 end
) as count2
from Users

Answer 2

这很大程度上取决于你所说的“结合”：

一行

您可以使用Abhik's answer或类似的内容：

SELECT firstHalf.count, secondHalf.count
FROM
    (SELECT COUNT(1) as count FROM Users WHERE joined BETWEEN '2014-01-01' AND '2014-06-30') firstHalf,
    (SELECT COUNT(1) as count FROM Users WHERE joined BETWEEN '2014-07-01' AND '2014-12-31') secondHalf;

多行

您可以使用UNION ALL同时运行查询并合并结果：

SELECT * FROM
 (SELECT COUNT(1) as count FROM Users WHERE joined BETWEEN '2014-01-01' AND '2014-06-30') firstHalf
UNION ALL
 (SELECT COUNT(1) as count FROM Users WHERE joined BETWEEN '2014-07-01' AND '2014-12-31') secondHalf;

您没有提出的问题

听起来你想得到半任意日期范围的计数。这就是GROUP BY与MySQL Date Operations相结合的含义。这将检索自2010年初以来加入的所有用户的计数，按年份分组，以及他们注册的年份的一半（0或1）。

SELECT YEAR(joined) as year, MONTH(joined) / 6 AS yearHalf, COUNT(*)
FROM Users
WHERE joined >= '2010-01-01'
GROUP BY YEAR(joined), MONTH(joined) / 6;

使用上面的查询格式，您可以轻松更改计算的细微程度，是否按年份分组等。

如何结合这些MySQL查询？

2 个答案: