[Tableau] - add support for GROUP BY X

[kuba--]

Tableau spreadsheet sends following requests:

SELECT SUBSTRING(`commits`.`commit_hash`, 1, 1024) AS `commit_hash`
FROM `commits`
  INNER JOIN `files` ON (SUBSTRING(`commits`.`repository_id`, 1, 1024) = SUBSTRING(`files`.`repository_id`, 1, 1024))
  INNER JOIN `repositories` ON (`commits`.`repository_id` = SUBSTRING(`repositories`.`repository_id`, 1, 1024))
GROUP BY 1

what gets an unknown error:

MySQL][ODBC 5.3(w) Driver][mysqld-5.5.10-Vitess]unknown error: GroupBy aggregate expression 'SUBSTRING(commits.commit_hash, 1, 1024) as commit_hash' doesn't appear in the grouping columns

SELECT SUBSTRING(`commits`.`commit_hash`, 1, 1024) AS `commit_hash`
FROM `commits`
  INNER JOIN `files` ON (SUBSTRING(`commits`.`repository_id`, 1, 1024) = SUBSTRING(`files`.`repository_id`, 1, 1024))
  INNER JOIN `repositories` ON (`commits`.`repository_id` = SUBSTRING(`repositories`.`repository_id`, 1, 1024))
GROUP BY 1

[kuba--]

Depends on issue:
#524