Implement COUNT DISTINCT

[gomesfernanda]

I'm running a query and seems to be having a problem

I'm using source{d} CE and I'm trying to see the unique collaborators for a specific repo.

I'm querying the "commits" table, and my query is:

SELECT COUNT(DISTINCT commit_author_name), repository_id
FROM commits
WHERE repository_id = 'data-intelligence'
GROUP BY repository_id

and I get the number 57.

However, when I run the query:

SELECT DISTINCT commit_author_name, repository_id
FROM commits
WHERE repository_id = 'data-intelligence'

I get the distinct names of
Marcelo Novaes
Fernanda Gomes
Máximo Cuadros

So, the unique number of collaborators is 3 but I get 57 if I do COUNT(DISTINCT commit_author_name).
I don't understand why.

The version of source{d} CE I'm using is v0.14.0-beta.3

[erizocosmico]

COUNT(DISTINCT x) is not implemented yet, sadly. It's something we know it's missing, but that has not been implemented yet.

You can work around this limitation using the following query:

SELECT COUNT(commit_author_name), repository_id
FROM (
  SELECT DISTINCT commit_author_name, repository_id
  FROM commits
  WHERE repository_id = 'data-intelligence'
) t
GROUP BY repository_id

[erizocosmico]

We should either:

• Implement count distinct
• Fail when there is an usage of count distinct, which is not supported

/cc @smola @ajnavarro

[ajnavarro]

we can start with the second choice, throw an error.

[ajnavarro]

Reopened because is not fixed on gitbase.

Right now we are going to return an error, but this issue should be kept to remind a future implementation.

[erizocosmico]

Waiting on src-d/go-mysql-server#785