Oprava počtu řádků při GROUP BY přes více sloupců (Nette Database Table)

[radimvaculik]

Problem

NetteDatabaseTableDataSource::getCount() generated invalid SQL for selections grouped by multiple columns. When a GROUP BY was present it built COUNT(DISTINCT col1, col2, ...), which:

• MySQL — is valid but ignores rows where any of the grouped columns is NULL, so the count is undercounted (returns 0 when every row has a NULL in one of the grouping columns).
• SQLite — is not supported at all and throws wrong number of arguments to function COUNT().

Fixes #991.

Fix

Count the number of groups via a subquery instead of relying on COUNT(DISTINCT ...):

SELECT COUNT(*) FROM (<original grouped query>) AS datagrid_count

This matches the approach already used by NetteDatabaseDataSource::getCount() and returns the correct count regardless of NULL values in the grouping columns. The duplicated GROUP BY handling in both branches of the method was consolidated into a single early check.

Tests

Added testGetCountWithGroupByMultipleColumns() reproducing the issue scenario (grouping by four columns with NULL values, 4 rows → 3 groups). getCount() now returns 3, consistent with getData().

make qa (PHPStan + phpcs) and the full test suite pass.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.95%. Comparing base (d9144ab) to head (c92fc68).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1294      +/-   ##
==========================================
+ Coverage   48.77%   48.95%   +0.17%     
==========================================
  Files          61       62       +1     
  Lines        2901     2905       +4     
==========================================
+ Hits         1415     1422       +7     
+ Misses       1486     1483       -3     

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