the result of a singleton select returned more than 1 value

  Explanation:  A singleton select statement  (SELECT...INTO)  may
  only  return  1  row  of  values.   The  result  table  for this
  singleton select contains more than one row.

  User Action:  Either embed the  SELECT  statement  (without  the
  INTO  clause)  in a DECLARE CURSOR statement and process it with
  OPEN and FETCH statements, or modify the SELECT statement so  it
  will return only one row.