Translate string.Join/Concat with ordering on SQLite

[Aykuttonpc]

Translates string.Join/string.Concat over an ordered grouping to SQLite's group_concat with an ORDER BY clause, supported since SQLite 3.44.0. Previously such queries fell back to client evaluation.

-- string.Join("|", g.OrderByDescending(e => e.Id).Select(e => e.String))
COALESCE(group_concat("b"."String", '|' ORDER BY "b"."Id" DESC), '')

Changes

• Add SqliteAggregateFunctionExpression (carries the orderings), mirroring SqlServerAggregateFunctionExpression
• SqliteStringAggregateMethodTranslator: stop refusing translation when an ordering is present; emit the new expression (plain group_concat when there's no ordering — SQL unchanged)
• SqliteQuerySqlGenerator: render group_concat(value, separator ORDER BY ...). Note SQLite places the ordering inside the parentheses, unlike SQL Server's WITHIN GROUP
• SqliteSqlNullabilityProcessor: handle the new expression
• Enable Join_with_ordering in StringTranslationsSqliteTest

Notes

• Scope is group_concat (string aggregation); ORDER BY is meaningless for Min/Max.
• group_concat(DISTINCT x ORDER BY y) is restricted in SQLite (DISTINCT + ORDER BY only when ordering by the distinct column); no base test covers this combination.

Fixes #32201

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[Copilot]

Pull request overview

This PR enables translation of string.Join/string.Concat over an ordered grouping in the SQLite provider by emitting SQLite’s group_concat(... ORDER BY ...) syntax (SQLite >= 3.44.0), avoiding client evaluation for these queries.

Changes:

• Introduces SqliteAggregateFunctionExpression to represent aggregate function invocations that carry ORDER BY information.
• Updates SQLite string-aggregate translation to allow ordered inputs and updates SQL generation to render ORDER BY inside the aggregate function parentheses.
• Enables the Join_with_ordering SQLite functional test to assert server translation.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/EFCore.Sqlite.FunctionalTests/Query/Translations/StringTranslationsSqliteTest.cs	Updates expected SQL for ordered string aggregation using group_concat(... ORDER BY ...).
src/EFCore.Sqlite.Core/Query/Internal/Translators/SqliteStringAggregateMethodTranslator.cs	Emits the new aggregate expression when orderings are present instead of refusing translation.
src/EFCore.Sqlite.Core/Query/Internal/SqliteSqlNullabilityProcessor.cs	Adds nullability-processing support for the new custom SQL expression node.
src/EFCore.Sqlite.Core/Query/Internal/SqliteQuerySqlGenerator.cs	Adds SQL generation for aggregate ORDER BY inside function parentheses.
src/EFCore.Sqlite.Core/Query/Internal/SqlExpressions/SqliteAggregateFunctionExpression.cs	New SQL expression type carrying aggregate function name, arguments, and orderings.

[Aykuttonpc]

Good catches all three addressed in b89fb2b: version-gated to 3.44 (falls back to client eval below that), DISTINCT + ORDER BY now refused, and the test is gated the same way.