This documentation is related to an older version of Firebolt. For the most current documentation, see Firebolt documentation.
NTH_VALUE
Returns the value evaluated of the nth row of the specified window frame (starting at the first row). If the specified row does not exist, NTH_VALUE returns NULL.
See also FIRST_VALUE, which returns the first value evaluated in the specified window frame.
Syntax
NTH_VALUE( <expr>, <n> ) OVER ( [ PARTITION BY <expr0> ] ORDER BY <expr1> [ASC|DESC] )
| Parameter | Description |
|---|---|
<expr> | A SQL expression of any type to evaluate. |
<n> | A constant integer in range [1, max of datatype INT] to indicate the row number to evaluate. |
<expr0> | An expression used for the PARTITION clause. |
<expr1> | An expression used for the order by clause. |
The return type of the function will be the same type as the expression to evaluate. This function respects NULL values, and results will be ordered with default null ordering NULLS LAST unless otherwise specified in the ORDER BY clause. If applied without an ORDER BY clause, the order will be undefined.
Example
The example below returns the student with the second highest test score for each grade level. Notice that the function returns NULL for the first row in each partition, unless the value of the expression for first and second rows of the partition are equal.
SELECT
first_name,
grade_level,
test_score,
NTH_VALUE(first_name, 2) OVER (PARTITION BY grade_level ORDER BY test_score DESC) second_highest_score
FROM
class_test;
Returns:
+------------+-------------+------------+----------------------+
| first_name | grade_level | test_score | second_highest_score |
+------------+-------------+------------+----------------------+
| Humphrey | 9 | 90 | null |
| Sammy | 9 | 85 | Sammy |
| Peter | 9 | 80 | Sammy |
| Iris | 9 | 79 | Sammy |
| Jojo | 9 | 78 | Sammy |
| Frank | 9 | 76 | Sammy |
| Shawn | 10 | 89 | null |
| Mary | 10 | 85 | Mary |
| Deborah | 10 | 78 | Mary |
| Albert | 10 | 59 | Mary |
| Yolinda | 10 | 30 | Mary |
| Roseanna | 11 | 94 | null |
| Shangxiu | 11 | 76 | Shangxiu |
| Otis | 11 | 75 | Shangxiu |
| Wanda | 11 | 73 | Shangxiu |
| Larry | 11 | 68 | Shangxiu |
| Carol | 11 | 52 | Shangxiu |
| Charles | 12 | 100 | Charles |
| Gary | 12 | 100 | Charles |
| Franco | 12 | 94 | Charles |
| Brunhilda | 12 | 92 | Charles |
| Jesse | 12 | 89 | Charles |
| Thomas | 12 | 66 | Charles |
+------------+-------------+------------+----------------------+