test(query): count a distinct join without a select

MySQL refuses a derived table with two columns of the same name. A
distinct join without a select projects the main table's columns next to
the joined `r._uid`, so the count holds it to keep those names apart on
every adapter.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: abnegate

tests/e2e/Adapter/Scopes/AggregationTests.php

@@ -2845,6 +2845,7 @@ public function testCountMatchesTheRowsOfGroupedDistinctAndAggregateReads(): voi
             'join with groupBy' => [[$join, Query::count('*', 'n'), Query::groupBy(['category'])], 4, 2],
             'distinct over a join' => [[$join, Query::distinct(), Query::select(['category'])], 4, 2],
             'distinct joined attribute' => [[$join, Query::distinct(), Query::select(['r.score'])], 5, 2],
+            'distinct over a join without a select' => [[$join, Query::distinct()], 6, 3],
             'full outer join with groupBy' => [[$fullOuterJoin, Query::count('*', 'n'), Query::groupBy(['r.score'])], null, null],
             'full outer join with distinct' => [[$fullOuterJoin, Query::distinct(), Query::select(['category'])], null, null],
         ];

tests/unit/RowCountTest.php

@@ -81,6 +81,7 @@ public static function shapes(): array
             'join with groupBy' => [[$join, Query::count('*', 'n'), Query::groupBy(['category'])], 4, 2],
             'distinct over a join' => [[$join, Query::distinct(), Query::select(['category'])], 4, 2],
             'distinct joined attribute' => [[$join, Query::distinct(), Query::select(['r.score'])], 5, 2],
+            'distinct over a join without a select' => [[$join, Query::distinct()], 6, 3],
             'emulated full outer join with groupBy' => [[$fullOuterJoin, Query::count('*', 'n'), Query::groupBy(['category'])], 4, 4],
             'emulated full outer join with distinct' => [[$fullOuterJoin, Query::distinct(), Query::select(['r.score'])], 6, 5],
         ];