BUGFIX: Only set distinct on count clause if explicitely set to improve performance

[Sebobo]

F.e. Postgres has performance issues with large datasets and the DISTINCT clause. In a test this change reduced the query time of a count query for ~900.000 entities by >80%.

In a custom project this affected their Neos Media.UI in which the following results were found:

• Count all assets | 580ms -> 260ms
• Query 20 assets | 690ms -> 350ms
• Query 100 assets | 990ms -> 650ms
• Module load | 1900ms -> 1400ms

Review instructions

Everything should work the same, as #415 already sets the distinct flag where (possibly) necessary.

Checklist

• Code follows the PSR-2 coding style
• Tests have been created, run and adjusted as needed
• The PR is created against the lowest maintained branch
• Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• Reviewer - The first section explains the change briefly for change-logs
• Reviewer - Breaking Changes are marked wit !!! and have upgrade-instructions

[albe]

I guess that's a good solution 👍. Regarding #415 I just noticed that it was actually reverted due to issues: #1293, but that should not have too much influence on this. Implicit joins were returning duplicates before, so counts on them were off. Now they're at least faster at that :D

[albe]

Or wait, I was never checking a $query->count() on implicit join results, but just the count($result)... https://github.com/neos/flow-development-collection/pull/1293/files#diff-b389146f7ff3bedefca76487b8b3421d40ebf42cb4f24e854d129897dacc03a8L269
So maaaaybeee this is indeed a bit more breaky than my last comment suggests. But breaky in the sense it behaves differently than before, though more logical, i.e. ->count() would return 2 now, when there is a duplicate result/2 result rows.

[Sebobo]

Setting a query as distinct should always be explicitly set and not assumed in any case?
Doctrine already does more magic than wished for in some cases.

[Sebobo]

Just got results from my customers production system (Postgres, 850.000 assets) based only on this change:

[kdambekalns]

LGTM