Example 1 - Analytics Database - Teradata Vantage

   SELECT x1 
   FROM table_1,
   (SELECT x2 
   FROM table_2
   UNION
   SELECT x3 
   FROM table_3
   ) derived_table;
   SELECT x1,y1 
   FROM table_1,
   (SELECT * 
   FROM table_2) derived_table(column_1, column_2)
   WHERE column_2 = 1 ;