Module transforms 

SQL AST Transforms

This module provides functions to transform SQL ASTs for dialect compatibility. These transforms are used during transpilation to convert dialect-specific features to forms that are supported by the target dialect.

Based on the Python implementation in sqlglot/transforms.py.

Functions

add_auto_table_alias

Add auto-generated table aliases (like _t0) for POSEXPLODE/EXPLODE in FROM clause when the alias has column_aliases but no alias name. This is needed for Spark target: FROM POSEXPLODE(x) AS (a, b) -> FROM POSEXPLODE(x) AS _t0(a, b)

add_recursive_cte_column_names

Add column names to recursive CTE definitions.

eliminate_distinct_on

Eliminate DISTINCT ON clause by converting to a subquery with ROW_NUMBER

eliminate_distinct_on_for_dialect

Eliminate DISTINCT ON with dialect-specific NULL ordering behavior.

eliminate_full_outer_join

Convert FULL OUTER JOIN to a UNION of LEFT and RIGHT OUTER joins.

eliminate_join_marks

Eliminate Oracle-style (+) join marks by converting to standard JOINs.

eliminate_qualify

Eliminate QUALIFY clause by converting to a subquery with WHERE filter

eliminate_semi_and_anti_joins

Convert SEMI and ANTI joins into equivalent forms that use EXISTS instead.

eliminate_window_clause

Inline window definitions from WINDOW clause.

ensure_bools

Ensure boolean values in conditions.

epoch_cast_to_ts

Convert epoch string in CAST to timestamp literal.

expand_between_in_delete

Expand BETWEEN expressions in DELETE statements to >= AND <=

expand_posexplode_duckdb

Expand POSEXPLODE in SELECT expressions for DuckDB.

explode_projection_to_unnest

Convert EXPLODE/POSEXPLODE in SELECT projections into CROSS JOIN UNNEST patterns.

explode_to_unnest

Convert EXPLODE to UNNEST (for standard SQL compatibility)

move_ctes_to_top_level

Move CTEs to the top level of the query.

no_comment_column_constraint

Convert COMMENT ON statements to inline comments.

no_ilike_sql

Convert ILIKE to LOWER(x) LIKE LOWER(y).

no_safe_cast_sql

Convert SafeCast to Cast.

no_trycast_sql

Convert TryCast to Cast.

preprocess

Apply a chain of transforms to an expression

propagate_struct_field_names

Convert BigQuery-style UNNEST aliases to column-alias format for DuckDB/Presto/Spark.

pushdown_cte_column_names

Push down CTE column names into SELECT expressions.

remove_precision_parameterized_types

Remove precision from parameterized types

replace_bool_with_int

Replace boolean literals for dialects that don’t support them

replace_int_with_bool

Replace integer literals for dialects that prefer boolean

simplify_nested_paren_values

Simplify nested parentheses around VALUES in FROM clause. Converts FROM ((VALUES (1))) to FROM (VALUES (1)) by stripping redundant wrapping. Handles various nesting patterns: Subquery(Paren(Values)), Paren(Paren(Values)), etc.

snowflake_flatten_projection_to_unnest

Snowflake-specific rewrite to mirror Python sqlglot’s explode_projection_to_unnest behavior when FLATTEN appears in a nested LATERAL within a SELECT projection.

strip_unnest_column_refs

Strip UNNEST wrapping from column reference arguments for Redshift target. BigQuery UNNEST(column_ref) -> Redshift: just column_ref

unnest_alias_to_column_alias

This walks the entire expression tree to find SELECT statements and converts UNNEST aliases in their FROM clauses and JOINs.

unnest_from_to_cross_join

Move UNNEST items from FROM clause to CROSS JOINs without changing alias format. Used for BigQuery -> BigQuery/Redshift where we want CROSS JOIN but not _t0(col) aliases.

unnest_generate_date_array_using_recursive_cte

Convert UNNEST(GENERATE_DATE_ARRAY(…)) to recursive CTE.

unnest_generate_series

Convert TABLE GENERATE_SERIES to UNNEST(GENERATE_SERIES(…)).

unnest_to_explode

Convert UNNEST to EXPLODE (for Spark/Hive compatibility)

unnest_to_explode_select

Convert CROSS JOIN UNNEST to LATERAL VIEW EXPLODE/INLINE for Spark/Hive/Databricks.

unqualify_columns

Remove table qualifiers from column references.

wrap_duckdb_unnest_struct

Wrap DuckDB UNNEST of struct arrays in (SELECT UNNEST(…, max_depth => 2)) subquery. BigQuery UNNEST of struct arrays needs this wrapping for DuckDB to properly expand struct fields.

wrap_unnest_join_aliases

Wrap UNNEST function aliases in JOIN items from AS name to AS _u(name) Used for PostgreSQL → Presto/Trino transpilation where GENERATE_SERIES is converted to UNNEST(SEQUENCE) and the alias needs the column-alias format.