feat(duckdb): Add transpilation support for positoinal column refs over values

[fivetran-amrutabhimsenayachit]

Issue: Snowflake uses $N to reference the Nth column of a VALUES clause (e.g. v1.$2). DuckDB also uses $N but for prepared-statement parameters — so the transpiled SQL would fail at runtime in DuckDB.

Fix: Added column_sql to DuckDB's generator. When it sees a $N column reference whose table alias points to a VALUES source in the same query, it rewrites it to DuckDB's native column name format (col0, col1, ...) — so v1.$2 becomes v1.col1.

[github-actions]

SQLGlot Integration Test Results

✅ All tests passed

Comparing:

• this branch (sqlglot:RD-1205932-transpile-bug-positional-column-ref-over-values @ sqlglot 4c1f7bf)
• baseline (main @ sqlglot 87b1da8)

Overall

main: 192441 total, 153536 passed (pass rate: 79.8%)

sqlglot:RD-1205932-transpile-bug-positional-column-ref-over-values: 186070 total, 148214 passed (pass rate: 79.7%)

Transitions:
No change

Dialect pair changes: 0 previous results not found, 2 current results not found

✅ All tests passed

[georgesittas]

Discussed in Slack/Jira: this is a more general issue with positional column refs which is not easy to transpile to DuckDB without invasive changes with considerable overhead.

Closing for now to avoid the complexity overhead in hot methods such as column_sql.