Ruby-on-rails 如何在rails中按行计算分组？
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How to count group by rows in rails?
提问by user199403
When I use User.count(:all, :group => "name"), I get multiple rows, but it's not what I want. What I want is the count of the rows. How can I get it?
当我使用时User.count(:all, :group => "name")，我得到多行，但这不是我想要的。我想要的是行数。我怎么才能得到它？
回答by nothing-special-here
Currently (18.03.2014- Rails 4.0.3) this is correct syntax:
目前（18.03.2014- Rails 4.0.3）这是正确的语法：
Model.group("field_name").count
It returns hash with counts as values e.g.
它返回带有计数作为值的哈希，例如
SurveyReport.find(30).reports.group("status").count
#=> {
"pdf_generated" => 56
}
回答by hgmnz
User.countwill give you the total number of users and translates to the following SQL:SELECT count(*) AS count_all FROM "users"User.count(:all, :group => 'name')will give you the list of unique names, along with their counts, and translates to this SQL:SELECT count(*) AS count_all, name AS name FROM "users" GROUP BY name
User.count将为您提供用户总数并转换为以下 SQL：SELECT count(*) AS count_all FROM "users"User.count(:all, :group => 'name')将为您提供唯一名称列表及其计数，并转换为以下 SQL：SELECT count(*) AS count_all, name AS name FROM "users" GROUP BY name
I suspect you want option 1 above, but I'm not clear on what exactly you want/need.
我怀疑你想要上面的选项 1，但我不清楚你到底想要/需要什么。
回答by sikachu
Probably you want to count the distinct name of the user?
可能您想计算用户的不同名称？
User.count(:name, :distinct => true)
would return 3 if you have user with name John, John, Jane, Joey (for example) in the database.
如果数据库中有名为 John、John、Jane、Joey（例如）的用户，则将返回 3。
________
| name |
|--------|
| John |
| John |
| Jane |
| Joey |
|________|
回答by sikachu
Try using User.find(:all, :group => "name").count
尝试使用 User.find(:all, :group => "name").count
Good luck!
祝你好运！
回答by CTS_AE
I found an odd way that seems to work. To count the rows returned from the grouping counts.
我发现了一种似乎有效的奇怪方法。对分组计数返回的行进行计数。
User Table Example
用户表示例
________
| name |
|--------|
| Bob |
| Bob |
| Joe |
| Susan |
|________|
Counts in the Groups
分组中的计数
User.group(:name).count
# SELECT COUNT(*) AS count_all
# FROM "users"
# GROUP BY "users"."name"
=> {
"Bob" => 2,
"Joe" => 1,
"Susan" => 1
}
Row Count from the Counts in the Groups
从组中的计数中计算行数
User.group(:name).count.count
=> 5
Something Hacky
一些黑客
Here's something interesting I ran into, but it's quite hacky as it will add the count to every row, and doesn't play too well in active record land. I don't remember if I was able to get this into an Arel / ActiveRecord query.
这是我遇到的一些有趣的事情，但它非常笨拙，因为它会将计数添加到每一行，并且在活动记录领域表现不佳。我不记得我是否能够将其放入 Arel/ActiveRecord 查询中。
SELECT COUNT(*) OVER() AS count, COUNT(*) AS count_all
FROM "users"
GROUP BY "users"."name"
[
{ count: 3, count_all: 2, name: "Bob" },
{ count: 3, count_all: 1, name: "Joe" },
{ count: 3, count_all: 1, name: "Susan" }
]
