SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 1)
    Function concatWithSeparator (children 1)
     ExpressionList (children 2)
      Literal \'a\'
      Literal \'b\'
   ExpressionList (children 1)
    Literal \'a\'
