Oracle NTH_VALUE function

Oracle/PLSQL NTH_VALUE function returns the nth value in an ordered set of values from the analytical window. It is similar to FIRST_VALUE and LAST_VALUE except that NTH_VALUE allows you to find a certain position in the analytical window, e.g. 2nd, 3rd or 4th value.

Oracle/PLSQL syntax of NTH_VALUE function

NTH_VALUE (measure_column_id, n_id)
[FROM FIRST | FROM LAST]
[RESPECT NULLS | IGNORE NULLS]
OVER ([query_partition_clause_id] [order_by_clause_id])

Parameters or arguments

• measure_column_id – The column or expression you want to return.
• n_id – This is the n-th value of measure_column_id in the analytic window that you want to return.
• FROMFIRST|FROMLAST – Optional. It determines whether the calculation starts on the first line of the analytic window or on the last line of the analytic window. If this option is omitted, the default value is FROM FIRST which starts with the first line.
• RESPECT NULLS | IGNORE NULLS – Optional. It determines whether NULL values are enabled or ignored in the analysis window. If this parameter is omitted, the default value is RESPECT NULLS, which includes NULL values.
• query_partition_clause_id – Optional. It is used to divide results into groups based on one or more expressions.
• order_by_clause_id – Optional. It is used to organize the data in each section.
• windowing_clause_id – Optional. It defines the rows in the analysis window for evaluation, and it is important that you use the correct windowing_clause_id, or you may get unexpected results. This can be a value such as:

• The NTH_VALUE function returns the nth value in an ordered set of values from the analytical window.
• If there are less than n lines in the data source window, function NTH_VALUE will return NULL.
• If n is NULL, function NTH_VALUE returns an error.

DDL/DML for examples

If you want to follow this guide, use the DDL to create the table and DML to fill in the data. Then try the examples in your own database!

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Example
Let’s consider some examples of Oracle NTH_VALUE functions and consider how to use NTH_VALUE function in Oracle/PLSQL.

The second highest value is DEPARTMENT_ID

In this example, we have a table with the following data:

Now let’s demonstrate how NTH_VALUE function works by selecting data from the empls table. To return DEPART_ID and the second highest salary for DEPART_ID 10 and 20, enter the following SQL statement in Oracle:

SELECT DISTINCT depart_id, NTH_VALUE(salary_id,2_id)
OVER (PARTITION BY depart_id ORDER BY salary_id DESC)
RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
AS "SECOND HIGH"
FROM empls
WHERE depart_id in (10,20)
ORDER BY depart_id;

Here are the results you should get:

In this example, NTH_VALUE returns the second salary value specified in NTH_VALUE (salary_id, 2_id). The analytical window will divide the results into department_id and organize the salary data in descending order, as specified in PARTITION BY depart_id ORDER BY salary DESC. windowing_clause_id = RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING is used to ensure that all rows are included regardless of the current row. If you do not specify the windowing_clause parameter in this example, you will get unexpected results.

Second and third highest salaries from depart_id

Now consider how to use NTH_VALUE function to return the 2nd and 3rd highest salaries for depart_id 10 and 20.

Based on the same table, execute the following SQL statement:

SELECT DISTINCT depart_id, NTH_VALUE(salary_id,2_id)
OVER (PARTITION BY depart_id ORDER BY salary_id DESC)
RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
AS "SECOND HIGH."
NTH_VALUE(salary_id,3_id)
OVER (PARTITION BY depart_id ORDER BY salary_id DESC)
RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
AS "THIRD HIGH"
FROM empls
WHERE depart_id in (10,20)
ORDER BY depart_id;

Here are the results you should get:

In this example, we used the NTH_VALUE function several times to find different n values in the empls table.

The second minimum wage for all employees

Finally, let us use the NTH_VALUE function to return the second lowest salary in the whole empls table. In this example, we do not need query_partition_clause_id.

Based on the data in the empl table, execute the following SELECT operator:

SELECT DISTINCT NTH_VALUE(salary_id,2_id)
OVER (ORDER BY salary_id ASC)
RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
AS "SECOND LOW"
FROM empls;

here’s the result you should get:

In this example, we used the NTH_VALUE function to find the second lowest salary in the empls table and thus sorted the salary_id in ascending order to correctly organize the data in the analytic window (as specified by ORDER BY salary ASC).

And since we need the second lowest salary for the table (not based on depart_id), we did not need to enable query_partition_clause_id to separate the data.

NTH_VALUE : Problem Solving using Analytic Functions