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SQLite: implement sum and average aggregation for decimal #33721

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merged 5 commits into from
May 29, 2024

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ranma42
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@ranma42 ranma42 commented May 15, 2024

Contributes to #19635

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        Summary of the changes
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        - Detail 2

        Fixes #bugnumber
  • Tests for the changes have been added (for bug fixes / features)
  • Code follows the same patterns and style as existing code in this repo

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ranma42 commented May 15, 2024

Some notes:

  • I ended up duplicating CombineTerms
    private SqlExpression CombineTerms(EnumerableExpression enumerableExpression, SqlExpression sqlExpression)
    {
    if (enumerableExpression.Predicate != null)
    {
    if (sqlExpression is SqlFragmentExpression)
    {
    sqlExpression = _sqlExpressionFactory.Constant(1);
    }
    sqlExpression = _sqlExpressionFactory.Case(
    new List<CaseWhenClause> { new(enumerableExpression.Predicate, sqlExpression) },
    elseResult: null);
    }
    if (enumerableExpression.IsDistinct)
    {
    sqlExpression = new DistinctExpression(sqlExpression);
    }
    return sqlExpression;
    }
    It looks like most IAggregateMethodCallTranslator implementations are re-implementing this same operation, so it might be ok (even intentional to keep them independent), but I was not expecting it at first
  • I am not 100% confident about the handling of nullability:
    • in LINQ .Sum over an empty decimal enumerable returns a decimal 0
    • in LINQ .Sum over an empty decimal? enumerable returns a decimal? null
    • in LINQ .Sum over an empty decimal? enumerable returns a decimal? 0
    • in LINQ .Sum over a decimal? with some null would return null (I believe)
    • in LINQ .Sum over a decimal? with some nulls would ignore all of them
      being unsure, I replicated the handling of SUM
      if (sqlFunctionExpression.IsBuiltIn
      && string.Equals(sqlFunctionExpression.Name, "SUM", StringComparison.OrdinalIgnoreCase))
      {
      nullable = false;
      return _sqlExpressionFactory.Coalesce(
      sqlFunctionExpression.Update(instance, arguments),
      _sqlExpressionFactory.Constant(0, sqlFunctionExpression.TypeMapping),
      sqlFunctionExpression.TypeMapping);
      }
  • adding/removing the CombineTerms step does not affect any of the existing tests; I plan to add at least a test that checks for that, but I might need some guidance in what is the best place to do so (should it be sqlite-specific or generic?)
  • adding/removing the nullability processing changes the SQL output, hence its effect is tested. OTOH, the results of the evaluation seem to pass regardless of that change, which might point out that additional tests are needed for that as well

EDIT: corrected notes on LINQ .Sum() after testing

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ranma42 commented May 15, 2024

combined sum+avg as suggested in #33720 (comment)
the max/min aggregation is left for a future PR as it might involve additional design around how to handle other types (ulong, TimeSpan, etc)

@ranma42 ranma42 changed the title Implement sum aggregation for decimal in SQLite Implement sum and average aggregation for decimal in SQLite May 15, 2024
@roji roji requested a review from cincuranet May 15, 2024 15:31
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@ranma42 Can you please resolve the conflict and then I can merge. Thanks.

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ranma42 commented May 28, 2024

@cincuranet rebased 👍

@cincuranet cincuranet merged commit d8fc38e into dotnet:main May 29, 2024
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cincuranet commented May 29, 2024

Thanks. Table in #19635 updated.

@ranma42 ranma42 deleted the sqlite-ef_sum branch May 29, 2024 17:29
@roji roji changed the title Implement sum and average aggregation for decimal in SQLite SQLite: implement sum and average aggregation for decimal Sep 23, 2024
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3 participants