SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 3)
   ExpressionList (children 1)
    Identifier id
   TablesInSelectQuery (children 1)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      TableIdentifier t1
   Function equals (children 1)
    ExpressionList (children 2)
     Function tuple (children 1)
      ExpressionList (children 2)
       Identifier s1
       Literal NULL
     Literal Tuple_(\'a\', NULL)
