Quote pushdown identifiers and stabilize MSSQL projection aliases - #18
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apply_polars_io_source_exprs wraps the source query in a subquery and adds the outer projection/predicate for column and predicate pushdown. When the source projection used unquoted reserved words, mixed-case names, or names with special characters, the generated outer references could fail to resolve or bind to the wrong column depending on the target dialect. - Quote outer projection identifiers for dialects SQLGlot recognizes. - Quote the leaf identifiers of pushed-down predicate columns. - For MSSQL, stabilize the output-defining SELECT: quote explicit aliases and give simple columns an explicit quoted alias, following only the leftmost output branch of set operations / parenthesized queries and leaving CTE bodies untouched. Adds _is_known_dialect, _quote_column_leaf_identifier, _leftmost_output_select, and _stabilize_mssql_projection_aliases, plus tests covering the quoting matrix across dialects and the MSSQL stabilization edge cases. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Signed-off-by: Pascal Tomecek <40371786+ptomecek@users.noreply.github.com>
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When
apply_polars_io_source_exprswraps a source query in a subquery and adds the outer projection/predicate for column and predicate pushdown, unquoted identifiers could fail to resolve or bind to the wrong column — reserved words (e.g.group), mixed-case names, or names with special characters, depending on the target dialect.Changes
New helpers:
_is_known_dialect,_quote_column_leaf_identifier,_leftmost_output_select,_stabilize_mssql_projection_aliases.apply_polars_io_source_exprsis shared byscan_dbandscan_clickhouse, so both benefit.Tests: quoting matrix across dialects (postgres/oracle/snowflake), metadata-name round-trips through duckdb, predicate-leaf quoting scope, and MSSQL stabilization edge cases (idempotency, CTE bodies, parenthesized set operations, projection order). Full
test_lazy_sql_reader(108) andtest_lazy_clickhouse_reader(10) pass; ruff clean.