message: Issue NTH_VALUE
  Add error coverage tests.
diff: @@ -95,6 +95,22 @@ sales 3 4
  sales 4 4
  # nth_value
  +statement error
  +SELECT depname, empno,
  + nth_value(empno) OVER (
  + PARTITION BY depname ORDER BY empno ASC
  + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
  + ) fv
  +FROM empsalary
  +
  +statement error
  +SELECT depname, empno,
  + nth_value(empno, 2, 3) OVER (
  + PARTITION BY depname ORDER BY empno ASC
  + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
  + ) fv
  +FROM empsalary
  +
  query III
  SELECT depname, empno,
  nth_value(empno, 2) OVER (
  