fix(bigquery): Do not generate null ordering on agg funcs (#4172)

* fix(bigquery): Do not generate NULLS LAST on asc agg funcs

* PR Feedback 1

sqlglot/generator.py

@@ -203,7 +203,8 @@ class Generator(metaclass=_Generator):
     }
 
     # Whether null ordering is supported in order by
-    # True: Full Support, None: No support, False: No support in window specifications
+    # True: Full Support, None: No support, False: No support for certain cases
+    # such as window specifications, aggregate functions etc
     NULL_ORDERING_SUPPORTED: t.Optional[bool] = True
 
     # Whether ignore nulls is inside the agg or outside.
@@ -2345,6 +2346,18 @@ def ordered_sql(self, expression: exp.Ordered) -> str:
                     f"'{nulls_sort_change.strip()}' translation not supported in window functions"
                 )
                 nulls_sort_change = ""
+            elif (
+                self.NULL_ORDERING_SUPPORTED is False
+                and (isinstance(expression.find_ancestor(exp.AggFunc, exp.Select), exp.AggFunc))
+                and (
+                    (asc and nulls_sort_change == " NULLS LAST")
+                    or (desc and nulls_sort_change == " NULLS FIRST")
+                )
+            ):
+                self.unsupported(
+                    f"'{nulls_sort_change.strip()}' translation not supported for aggregate functions with {sort_order} sort order"
+                )
+                nulls_sort_change = ""
             elif self.NULL_ORDERING_SUPPORTED is None:
                 if expression.this.is_int:
                     self.unsupported(

tests/dialects/test_bigquery.py

@@ -1985,3 +1985,17 @@ def test_range_type(self):
         self.validate_identity(
             "SELECT RANGE(CAST('2022-10-01 14:53:27 America/Los_Angeles' AS TIMESTAMP), CAST('2022-10-01 16:00:00 America/Los_Angeles' AS TIMESTAMP))"
         )
+
+    def test_null_ordering(self):
+        # Aggregate functions allow "NULLS FIRST" only with ascending order and
+        # "NULLS LAST" only with descending
+        for sort_order, null_order in (("ASC", "NULLS LAST"), ("DESC", "NULLS FIRST")):
+            self.validate_all(
+                f"SELECT color, ARRAY_AGG(id ORDER BY id {sort_order}) AS ids FROM colors GROUP BY 1",
+                read={
+                    "": f"SELECT color, ARRAY_AGG(id ORDER BY id {sort_order} {null_order}) AS ids FROM colors GROUP BY 1"
+                },
+                write={
+                    "bigquery": f"SELECT color, ARRAY_AGG(id ORDER BY id {sort_order}) AS ids FROM colors GROUP BY 1",
+                },
+            )