unified string formatting

Author: A-Baji

datajoint/expression.py

@@ -634,10 +634,11 @@ def make_sql(self):
         if not arg1.heading.secondary_attributes and not arg2.heading.secondary_attributes:
             # no secondary attributes: use UNION DISTINCT
             fields = arg1.primary_key
-            return ("SELECT * FROM (({sql1}) UNION ({sql2})) as `_u%x`".format(
+            return ("SELECT * FROM (({sql1}) UNION ({sql2})) as `_u{alias}`".format(
                 sql1=arg1.make_sql() if isinstance(arg1, Union) else arg1.make_sql(fields),
                 sql2=arg2.make_sql() if isinstance(arg2, Union) else arg2.make_sql(fields),
-                )) % next(self.__count)
+                alias=next(self.__count)
+                ))
         # with secondary attributes, use union of left join with antijoin
         fields = self.heading.names
         sql1 = arg1.join(arg2, left=True).make_sql(fields)