add null_if_any_null flag

Author: fivetran-felixhuang

sqlglot/dialects/bigquery.py

@@ -164,6 +164,13 @@ def _build_timestamp(args: t.List) -> exp.Timestamp:
     return timestamp
 
 
+def _build_greatest(args: t.List) -> exp.Greatest:
+    """Build GREATEST with BigQuery's null-if-any-null behavior."""
+    greatest = exp.Greatest.from_arg_list(args)
+    greatest.null_if_any_null = True
+    return greatest
+
+
 def _build_date(args: t.List) -> exp.Date | exp.DateFromParts:
     expr_type = exp.DateFromParts if len(args) == 3 else exp.Date
     return expr_type.from_arg_list(args)
@@ -545,6 +552,7 @@ class Parser(parser.Parser):
             "EDIT_DISTANCE": _build_levenshtein,
             "FORMAT_DATE": _build_format_time(exp.TsOrDsToDate),
             "GENERATE_ARRAY": exp.GenerateSeries.from_arg_list,
+            "GREATEST": _build_greatest,
             "JSON_EXTRACT_SCALAR": _build_extract_json_with_default_path(exp.JSONExtractScalar),
             "JSON_EXTRACT_ARRAY": _build_extract_json_with_default_path(exp.JSONExtractArray),
             "JSON_EXTRACT_STRING_ARRAY": _build_extract_json_with_default_path(exp.JSONValueArray),

sqlglot/dialects/duckdb.py

@@ -405,6 +405,37 @@ def _initcap_sql(self: DuckDB.Generator, expression: exp.Initcap) -> str:
     return _build_capitalization_sql(self, this_sql, escaped_delimiters_sql)
 
 
+def _greatest_sql(self: DuckDB.Generator, expression: exp.Greatest) -> str:
+    """
+    Handle GREATEST function with dialect-aware NULL behavior.
+
+    - If null_if_any_null=True (BigQuery-style): return NULL if any argument is NULL
+    - If null_if_any_null=False (DuckDB/PostgreSQL-style): ignore NULLs, return greatest non-NULL value
+    """
+    all_args = [expression.this] + expression.expressions
+    greatest_expr = self.func("GREATEST", *all_args)
+
+    # Check if this GREATEST should return NULL if any arg is NULL (BigQuery behavior)
+    if getattr(expression, 'null_if_any_null', False):
+        # BigQuery behavior: NULL if any argument is NULL
+        null_checks = []
+        for arg in all_args:
+            null_checks.append(exp.Is(this=arg, expression=exp.Null()))
+
+        is_any_null_expr: exp.Expression = null_checks[0]
+        for null_check in null_checks[1:]:
+            is_any_null_expr = exp.Or(this=is_any_null_expr, expression=null_check)
+
+        # Create CASE expression
+        case_expr = exp.Case(
+            ifs=[exp.If(this=is_any_null_expr, true=exp.Null())], default=greatest_expr
+        )
+        return self.sql(case_expr)
+    else:
+        # DuckDB/PostgreSQL behavior: use native GREATEST (ignores NULLs)
+        return self.sql(greatest_expr)
+
+
 class DuckDB(Dialect):
     NULL_ORDERING = "nulls_are_last"
     SUPPORTS_USER_DEFINED_TYPES = True
@@ -866,6 +897,7 @@ class Generator(generator.Generator):
             exp.EuclideanDistance: rename_func("LIST_DISTANCE"),
             exp.GenerateDateArray: _generate_datetime_array_sql,
             exp.GenerateTimestampArray: _generate_datetime_array_sql,
+            exp.Greatest: _greatest_sql,
             exp.GroupConcat: lambda self, e: groupconcat_sql(self, e, within_group=False),
             exp.Explode: rename_func("UNNEST"),
             exp.IntDiv: lambda self, e: self.binary(e, "//"),

sqlglot/expressions.py

@@ -6694,6 +6694,7 @@ class Getbit(Func):
 class Greatest(Func):
     arg_types = {"this": True, "expressions": False}
     is_var_len_args = True
+    null_if_any_null = False  # Set to True for BigQuery-style NULL behavior
 
 
 class GreatestIgnoreNulls(Func):