按日期分组的循环变量 [英] Loop variable grouping by date

问题描述

我有一些体育比赛的结果，我想遍历这些结果并在表格中的日期下分组.例如;

I have some sporting results that i'd like to loop through and group under dates in a table. For example;

|Sat, 20|
|Game 1 Results|
|Game 2 Results|
|Sun, 21|
|Game 3 Results|
|Sat, 27|
|Game 4 Results|

我的控制器

@matches = Match.group([:matchId, 'DATE(matchDate)']).inject([]) do |results, matches|
           team_names = Match.where(matchId: matches.matchId)
           results << [matches.id, matches.matchDate, team_names.first.team.name, team_names.last.team.name, team_names.first.points, team_names.last.points]
end

目前我正在做一个基本的循环，正在显示.

At the moment i'm doing a basic loop, which is showing.

|Sat, 20|
|Game 1 Results|
|Sat, 20|
|Game 2 Results|
|Sun, 21|
|Game 3 Results|
|Sat, 27|
|Game 4 Results|

推荐答案

SQL GROUP BY 用于聚合值:您可以获得每个日期的匹配次数，或目标总和，等等上.(在此处阅读更多内容.)但如果您想要所有游戏的列表，请按组不太合适.

SQL GROUP BY is for aggregating values: you can get the count of matches per date, or the sum of goals, and so on. (Read more here.) But if you want a list of all games in groups, it's not a good fit.

您看到两次相同的日期，因为您按日期和匹配 ID 分组.

You're seeing the same date twice because you're grouping by the date and the match ID.

如果你没有很多数据，你可以用 Ruby 代码来完成:

If you don't have a lot of data, you could do it all in Ruby code:

Match.all.group_by { |match| match.matchDate.to_date }

这为您提供了一个以日期为键、匹配列表为值的散列.

This gives you a hash with dates as keys and lists of matches as values.

此答案假定 matchDate 是时间，因为您在示例中使用了 DATE(matchDate).如果它已经是日期，则不需要上面的 .to_date 位.

This answer assumes that matchDate is a time, because you used DATE(matchDate) in your example. If it's already a date, you don't need the .to_date bit above.

另请注意，SQL 中的DATE(a_time_column) 将提取数据库时区中的日期.Rails 通常将数据库配置为在内部使用 UTC 时区.因此，如果您确实使用这样的数据库查询，请注意这一点并确保您获得正确的日期.

Also note that DATE(a_time_column) in SQL will extract the date in the database time zone. Rails often has the database configured to use the UTC time zone internally. So if you do go with a database query like that, be aware of this and make sure you get the right date.

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