[xperiandri]

Draft, do not merge. SQLProvider 1.5.27 depends on the nested layout this PR removes: a third for over an independent table fails there with "no such column", and two of its own tests fail. EF Core for SQL Server also stops translating two shapes that rely on a lateral join: an in-memory collection as the middle for, and a group read again after a for over it and a join. Kept for discussion of a narrower design for #8459.

Stacked on #20894

Over an IQueryable, a third for, a yield! or a join after two fors now continues one chain of SelectMany, Join and GroupJoin, as C# builds it, so the two left joins spelled groupJoin … into g and for x in g.DefaultIfEmpty() in #8459 become two SQL LEFT JOINs.

Details

• The rest of the query used to be nested in the collection selector of the first SelectMany. EF Core translates that only as a lateral join (APPLY), which SQLite lacks, and not at all when a join is nested there.
• A join whose inner source or inner key uses the variable of an earlier for stays nested, since it differs per outer element.
• What follows a leftOuterJoin is translated as before.

🤖 Generated with Claude Code

[github-actions]

✅ Release notes checked

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✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
`src/FSharp.Core`	docs/release-notes/.FSharp.Core/11.0.200.md

[xperiandri]

Covered cases

EF Core SQLite translates 99 of 138 scenarios, 92 without this change. Now translated: for over two levels of navigation collections, three and four fors, if … then between three fors, join and groupJoin after two fors, and two left joins spelled groupJoin and DefaultIfEmpty.

Not changed: a join whose inner source or inner key uses a variable of an earlier for stays nested, and EF Core needs APPLY for it, as for the equivalent C#. What follows a leftOuterJoin stays as it was.

Why this is a draft

• SQLProvider 1.5.27 on SQLite: a third for over an independent table, or over a navigation for followed by an independent table, fails with "no such column: pair.Id", and its tests simple select cross-join test 3 tables and simple select join and cross-join test fail. Its cross-join branch takes the name of the projection parameter as a table alias; the nested shape never reached it.
• EF Core for SQL Server: for c in db.Customers do for n in ns do for o in c.Orders … with ns an in-memory collection, and a group read again after a for over it and a join, translate on main and no longer do.