SQL: lower ORDER BY on a qualified column after a join (ambiguous names are rejected now) #652

Found in the #539 review.

Problem

SELECT a.k, b.k FROM a JOIN b ON a.id = b.id ORDER BY b.k used to sort by a.k without any error. The SQL lowering emits the Project above the join with qualifier: None, so its output schema loses each column's source table. The resolver then failed to find b.k by (table, name) and fell back to the first column named k.

Status

#539 makes this fallback safe: it now applies only when exactly one column has that name. Otherwise resolution fails. The query above is now rejected instead of being lowered wrongly.

Follow-up

Make such queries lower correctly. The obstacle is that the IR's Project has a single qualifier for all of its output columns (#573 §4.2.2 relies on this), so a pass-through column cannot keep its own source table. Options:

• per-column qualifiers on Project;
• resolving ORDER BY against the pre-projection scope in the frontend.

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https://claude.ai/code/session_01W7qG9aFyPij5uWsyAJCxDW