OBSL-1027: SQL AST window functions + UNION-in-CTE

[mivds]

PR chain (soda-core)

1. OBSL-1013: ship table discovery in soda-core (soda data-source discover) #2773 — ship table/column discovery
2. OBSL-1025: emit metrics[] in scan-results payload when measurements present #2774 — emit metrics[] in scan-results payload
3. OBSL-1027: SQL AST window functions + UNION-in-CTE #2776 — SQL AST window functions + UNION-in-CTE ← this PR
4. OBSL-1019/1007 (soda-core part): raw feature-config passthroughs on the dataset-config DTO + MM/dialect seams #2777 — raw feature-config passthrough (config DTO)
5. All-datasource dialect groundwork: time/interval, percentile, typed timestamp literal, NaN filter #2787 — all-datasource dialect groundwork

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Summary

Adds the SQL-AST primitives the v3 numeric profiler needs, unblocking the profiling SQL port (OBSL-1017). Scope was determined by the OBSL-1014 spike.

• WINDOW_FUNCTION AST node (sql_ast.py) — name, args, optional partition_by: list[COLUMN], optional order_by (reuses ORDER_BY_ASC/ORDER_BY_DESC). Renders NAME(args) OVER ([PARTITION BY ...] [ORDER BY ...]).
• UNION-in-CTE — widened CTE.cte_query to accept UNION (covers UNION_ALL); _build_cte renders it via build_union_sql.
• Rendering reuses existing function-arg + ORDER BY logic; additive dispatch branch in build_expression_sql.

Rendered output examples (asserted in tests): ROW_NUMBER() OVER (ORDER BY "value_" DESC), SUM("amount") OVER (PARTITION BY "category" ORDER BY "id" ASC), CTE bodies containing UNION / UNION ALL.

Stacked on #2774 (OBSL-1025) → #2773 (OBSL-1013). Closes the AST gap from the OBSL-1014 spike.

Test Plan

• 7 new unit tests asserting rendered SQL (window fns w/ partition+order, no-clause, multi-col partition, CTE UNION/UNION ALL)
• Regression: soda-tests/tests/unit → 993 passed, 2 skipped, 0 failures
• pre-commit (isort/black/autoflake) clean

🤖 Generated with Claude Code

[m1n0]

Reviewed. Clean — no findings. The new node follows the existing patterns closely: __post_init__ parent-node wiring matches FUNCTION's, the ASC/DESC rendering is the same isinstance idiom the SELECT-level order-by builder already uses (sql_dialect.py:1152), UNION_ALL subclasses UNION so the CTE branch covers both, and .AS() aliasing works generically via the ALIAS wrapper. Rendering is pinned by tests incl. the OVER () edge case. CI green.

Two passing notes, neither actionable here:

• partition_by is list[COLUMN] rendered via _build_column_sql, so partition-by-expression isn't supported — fine for the profiler port, just flagging the boundary.
• CTE-UNION now leans on build_union_sql, which carries a pre-existing "only tested/verified for Postgres" TODO (sql_dialect.py:683) — the profiling SQL port will inherit that caveat on other dialects.

[mivds]

No code changes — agreed it's clean. The two boundary notes are real but out of scope here: partition-by-expression (partition_by is list[COLUMN]) isn't needed for the profiler port, and build_union_sql's "Postgres-only" TODO is pre-existing and inherited by the profiling SQL port on other dialects. Flagging both for the follow-up rather than expanding this PR.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud