Fix: don't change query if no join marks in eliminate_join_marks, fixes #4721

Author: georgesittas

sqlglot/transforms.py

@@ -934,7 +934,8 @@ def eliminate_join_marks(expression: exp.Expression) -> exp.Expression:
             new_from_name = list(only_old_joins)[0]
             query.set("from", exp.From(this=old_joins[new_from_name].this))
 
-        query.set("joins", list(new_joins.values()))
+        if new_joins:
+            query.set("joins", list(new_joins.values()))
 
         if not where.this:
             where.pop()

tests/test_transforms.py

@@ -174,6 +174,13 @@ def test_remove_precision_parameterized_types(self):
 
     def test_eliminate_join_marks(self):
         for dialect in ("oracle", "redshift"):
+            # No join marks => query remains unaffected
+            self.validate(
+                eliminate_join_marks,
+                "SELECT a.f1, b.f2 FROM a JOIN b ON a.id = b.id WHERE a.blabla = 'a'",
+                "SELECT a.f1, b.f2 FROM a JOIN b ON a.id = b.id WHERE a.blabla = 'a'",
+                dialect,
+            )
             self.validate(
                 eliminate_join_marks,
                 "SELECT T1.d, T2.c FROM T1, T2 WHERE T1.x = T2.x (+) and T2.y (+) > 5",