Document aggregate queries and built-in function mapping

[Copilot]

EF Core lacked consolidated guidance for aggregate projections, composed aggregate inputs, and provider-specific top-level aggregates. Built-in database function mapping via IsBuiltIn was also undocumented.

• Aggregate queries
  • Document GroupBy projections with filtering, ordering, and distinct inputs.
  • Show the constant-group workaround for provider-specific top-level aggregates.
  • Note that aggregate UDF mapping is unsupported.

var standardDeviation = context.Posts
    .GroupBy(_ => 1)
    .Select(g => EF.Functions.StandardDeviationSample(g.Select(p => p.Rating)))
    .FirstOrDefault();

• Function mapping

  • Document fluent .IsBuiltIn() and [DbFunction(IsBuiltIn = true)] configuration.
  • Add a corresponding sample.

• Provider references

  • Link SQL Server and SQLite aggregate translation tables to the conceptual guidance.

• Fixes Document aggregate functions #4002
• Fixes Document new IsBuiltIn API and property on DbFunctionAttribute #2476

[Copilot]

Pull request overview

Documents aggregate query composition, top-level aggregate workarounds, and built-in database function mapping.

Changes:

• Adds aggregate query guidance and examples.
• Documents IsBuiltIn configuration with a sample.
• Cross-links SQL Server and SQLite provider references.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
samples/core/Querying/UserDefinedFunctionMapping/Model.cs	Adds built-in function mapping sample.
entity-framework/core/querying/user-defined-function-mapping.md	Documents fluent and attribute configuration.
entity-framework/core/querying/complex-query-operators.md	Adds aggregate query guidance.
entity-framework/core/providers/sqlite/functions.md	Links conceptual aggregate guidance.
entity-framework/core/providers/sql-server/functions.md	Links conceptual aggregate guidance.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.