feat(sql): GROUP BY, aggregates, DISTINCT, LIKE, IN (SQLR-3)

[joaoh82]

Summary

Closes the analytical-SQL gap that was sitting under "Possible extras":

• LIKE / NOT LIKE / ILIKE with %, _, \-escape; case-insensitive ASCII to match SQLite's default
• IN (list) / NOT IN (list); subquery form rejected with NotImplemented
• SELECT DISTINCT (single + multi-column; NULL == NULL for dedupe)
• GROUP BY on bare columns (acts like implicit DISTINCT when no aggregates)
• Aggregates: COUNT(*), COUNT([DISTINCT] col), SUM, AVG, MIN, MAX
• Column aliases (COUNT(*) AS n) and ORDER BY by alias or aggregate display form
• Friendly error when an aggregate name lands in WHERE

SUM stays INTEGER until a REAL input or i64 overflow promotes it once to REAL (SQLite-style). AVG always returns REAL (or NULL on empty / all-NULL groups).

What's not in this PR (filed as follow-ups)

• HAVING
• LIKE … ESCAPE '<char>'
• IN (subquery)
• DISTINCT on SUM/AVG/MIN/MAX
• GROUP BY on expressions
• Window functions, BETWEEN, GROUP_CONCAT, GLOB / REGEXP

Implementation map

• New module src/sql/agg.rs — AggState, DistinctKey, like_match. Pure-functional; no Database / Table coupling.
• src/sql/parser/select.rs — Projection becomes Items(Vec<ProjectionItem>), with ProjectionKind::{Column, Aggregate} and an optional alias. SelectQuery gains distinct: bool and group_by: Vec<String>. Parser validates that bare projection columns appear in GROUP BY.
• src/sql/executor.rs — adds Expr::Like, Expr::ILike, Expr::InList, Expr::InSubquery arms in eval_expr. New aggregation path in execute_select_rows that bypasses the rowid-shape optimizers (HNSW / FTS / bounded-heap) when grouping. DISTINCT post-pass and aggregate-aware ORDER BY by alias / display form.

Docs

• README.md feature table updated; "Possible extras" pruned.
• docs/supported-sql.md — full SELECT semantics rewrite (DISTINCT / GROUP BY / aggregates / LIKE / IN sections, with semantics callouts).
• docs/sql-engine.md — new "Aggregation phase" section under the executor doc.

Verification

• cargo build --workspace --exclude sqlrite-desktop --exclude sqlrite-python --exclude sqlrite-nodejs --all-targets — clean
• cargo fmt --all -- --check — clean
• cargo clippy --workspace --exclude sqlrite-desktop --exclude sqlrite-python --exclude sqlrite-nodejs --all-targets — no new warnings (only pre-existing ones unrelated to this PR)
• cargo test --workspace --exclude sqlrite-desktop --exclude sqlrite-python --exclude sqlrite-nodejs — engine tests went from 411 → 434 (+22 SQLR-3 integration tests + 12 new agg.rs unit tests; some pre-existing tests collapsed into new helpers)
• REPL smoke: CREATE, INSERT, LIKE, IN, DISTINCT, GROUP BY with all 5 aggregates + COUNT(DISTINCT) + ORDER BY n DESC — all render correctly via prettytable.

Test plan

• CI passes (build, fmt, clippy, tests)
• Local REPL smoke still green after rebase to main
• Sanity-check the README "Not yet supported" line still reads cleanly after the trim

🤖 Generated with Claude Code