postgresql - Is it possible to get a function result with columns which are not in the group by (SQL)? -

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I am trying to get the final registration date of a course, but I id Thar Max of the record is a function, so I should use the group from id , which I do not want, because the result is very different (only one record per ID per every record).

What's the way to manage a query like this ?: 

  SELECT id, MAX (registration_date) as a registration form;

Because it returns an error and I have to do this to avoid it: 

  SELECT id, MAX (registration_date) AS in the form of registration Group ID from registration ID;

And I do not want the result of the last one.

You can use the window function for: 

  SELECT id FROM (SELECT id, RANK) (override registration_dated DESC from the course of RCom) WHERE rk = 1

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