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task-46 - Specializer-SQL-support-SELECT-star-expansion.md

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id TASK-46
title Specializer SQL support: SELECT * star expansion
status Done
assignee
created_date 2026-07-26 11:42
updated_date 2026-07-26 12:20
labels
milestone m-7
dependencies
TASK-45
documentation
docs/superpowers/specs/2026-07-25-sql-specializer-design.md
type feature
ordinal 40000

Description

The single biggest corpus rung: 128 of 625 clean-unsupported corpus cases have SELECT * (or tbl.*) as their first blocker. Expand the star at bind time in the frontend against DuckDB's measured semantics — column order and naming for the row table alone and under joins (including duplicate-name handling), tbl.* qualified forms, and whatever star modifiers the corpus actually uses (EXCLUDE/REPLACE are measured-first: support only what the corpus needs, reject the rest cleanly by name). Pure frontend work — no IR, backend, or boundary changes. Clearing it also de-masks second blockers currently hidden behind star for the builtins wave (TASK-47).

Acceptance Criteria

  • #1 Star semantics pinned by measurement against DuckDB 1.5.5 (column order, duplicate-name policy, qualified tbl.*, modifier handling) and recorded as duck_check tests
  • #2 Corpus replay: star-first-blocker cases flip to match or to a NAMED deeper blocker; zero FAILs; match count and the new first-blocker tally recorded here
  • #3 Unsupported star forms (if any remain) reject with a clean "unsupported: ..." naming the form
  • #4 mise gate-specializer green

Implementation Plan

Stretch plan (recorded 2026-07-26 after the measurement spike; all facts below are measured on DuckDB 1.5.5). Corpus star census: 156 plain SELECT *, 26 tbl.*, 16 * EXCLUDE, 13 COLUMNS(...), 3 * LIKE, 2 * REPLACE, 2 mixed. Wave scope: plain *, tbl.*, EXCLUDE (~198 mentions); COLUMNS()/REPLACE/LIKE/RENAME/EXCEPT/ILIKE reject by name. All forms already parse under sqlparser 0.62 and funnel to the single rejection at frontend.rs:125 — one expansion site. Measured pins: expansion order is FROM order then declared column order per table; SELECT * FROM a JOIN b ON a.k=b.k emits DUPLICATE column names ('k','x','k','y') — unrepresentable in a pydantic output model, and any star item covering a joined static table necessarily includes its join-key column, whose projection our engine already cleanly rejects; therefore star items that cover a static table reject cleanly naming the key column (covers the duplicate-name shape too). __THIS__.* under a join is fine (row columns only). EXCLUDE: paren and bare forms; case-insensitive; unknown name = binder error mirroring DuckDB ("Column "nope" in EXCLUDE list not found"); duplicate list entry = error ("Duplicate entry"); unqualified EXCLUDE removes every same-named column.

  1. Binder::expand_star(qualifier, options) -> Vec<(name, SExpr)> using the existing SKind::Col / static_lane constructors; wire into the projection loop (mixed *, expr items fall out of item-position expansion); existing duplicate-output-name check stays as the final guard.
  2. duck_check pins for every measured behavior above incl. the EXCLUDE edges (exclude-all, EXCLUDE K case-folding) and clean-unsupported messages for the rejected forms.
  3. Corpus replay re-tally into this ticket (AC #2): flips + newly-surfaced second blockers.
  4. Gate green.

Implementation Notes

Landed in one pass: Binder::expand_star (frontend.rs) expands * and tbl.* at the single projection site using the existing SKind::Col / static_lane constructors — no IR/backend/boundary changes, exactly as scoped. EXCLUDE handles bare + paren forms case-insensitively (sqlparser 0.62 carries entries as ObjectName; single-part idents only, qualified entries reject by name); unknown-column and duplicate-entry EXCLUDE mirror DuckDB's binder errors; exclude-all falls through to the existing empty-SELECT bind error (same shape as DuckDB's "SELECT list is empty after resolving * expressions"). Star items covering a joined static table reject cleanly naming the join-key column (DuckDB includes the key AND emits duplicate output names there — both unrepresentable; __THIS__.* under a join works). ILIKE/EXCEPT/REPLACE/RENAME/COLUMNS() reject by name. CORPUS RESULT (AC #2): 53 -> 172 match of 678 (+119, a 3.2x coverage jump), 0 FAILs, 506 clean-unsupported. New first-blocker head: BETWEEN 31, comma join 30, dynamic-table alias 30, table-function FROM 24, then the builtin catalogue (array_slice 23, contains 18, damerau_levenshtein 17, ...) — the TASK-47 target list confirmed. Gate green: cargo 129 + pytest 627 (13 xfail incl. the pre-existing substr const-fold pin from master).

Final Summary

Merged as PR #30 (2026-07-26). Star expansion at the frontend's single projection site tripled corpus coverage: 53 -> 172 match of 678, zero FAILs. All measured edges pinned (order, EXCLUDE case-folding + binder errors, star-over-join rejection naming the join key, macro forms rejected by name). Gate green cargo 129 / pytest 627. Unblocked TASK-47's target list: post-star first-blocker head is BETWEEN 31, comma join 30, dynamic-table alias 30, then the builtin catalogue.