Add/fix support for distinct selects when using pagination

[uzegonemad]

This adds/fixes the ability to use select()->distinct()->paginate(). Previously, the count would be off because the count query disregarded distinct().

Fixes #3191

[taylorotwell]

I need better examples of what was fixed here. Post the incorrect SQL that was generated before and the Eloquent or query builder query used to generate it. Then post the correct SQL that is generated now.

[GrahamCampbell]

Please remove the extra space: if (is_null($columns)).

[uzegonemad]

@taylorotwell Good point - that is admittedly pretty vague.

Eloquent:

Header::select('query_serial_num', 'serial_num', 'motor_model_no')
      ->distinct()
      ->where('query_serial_num', 'like', $serial.'%')
      ->paginate(self::RESULTS_PER_PAGE);

Before fix:

# Count Query
select count(*) as aggregate from `header` where `query_serial_num` like ?

# Results Query
select distinct `query_serial_num`, `serial_num`, `motor_model_no` from `header` where `query_serial_num` like ? limit 50 offset 0

After fix:

# Count Query (changed)
select count(distinct `query_serial_num`, `serial_num`, `motor_model_no`) as aggregate from `header` where `query_serial_num` like ?

# Results Query (unchanged)
select distinct `query_serial_num`, `serial_num`, `motor_model_no` from `header` where `query_serial_num` like ? limit 50 offset 0

[swt83]

I have this issue also.

[myquote-dev]

We would also love to see this problem fixed! A brief test of uzegonemad's changes shows they do indeed seem to fix it.

With the current version of laravel (4.1) we are having to work around this problem by resorting to using DB::raw() queries for accurate pagination results when distinct() is used.

Hopefully a change can make it into 4.2!

[uzegonemad]

@taylorotwell I understand you're busy but do please let me know if there's any other information you need from me. Thanks!

[taylorotwell]

This broke the following situation and had to be reverted.

http://laravel.io/bin/rWexv

[uzegonemad]

Thanks for the heads up, maybe you have a better solution to the problem?

[Lambik]

I know this is very old, but I still seem to have the same issue in laravel 5.1.
Will there ever be a valid fix? The pastebin link is broken so I don't know what broke and caused the revert.