关于这一点:
Given a table that looks like this:
name
------
barry
dave
bill
dave
dave
barry
john
This query:
SELECT name, count(*) AS count FROM table GROUP BY name;
Will produce output like this:
name count
-------------
barry 2
dave 3
bill 1
john 1
对于ActiveModel来说，正确的Rails惯例是什么？
Distinct和Group By会给出不同的结果.为了得到你期望的结果，你需要使用
Person.group(:name).count
(1.2ms) SELECT COUNT(*) AS count_all, name AS name FROM "people" GROUP BY "people"."name"
=> {"Dan"=>3, "Dave"=>2, "Vic"=>1}
如上所示，该组将以散列形式返回内容.而distinct只返回总人数，如下所示.
Person.distinct(:name).count
(0.4ms) SELECT DISTINCT COUNT(DISTINCT "people"."id") FROM "people"
=> 6