Oracle / PLSQL: NTH_VALUE Function
This Oracle tutorial explains how to use the Oracle/PLSQL NTH_VALUE function with syntax and examples.
Description
The Oracle/PLSQL NTH_VALUE function returns the nth value in an ordered set of values from an analytic window. It is similar to the FIRST_VALUE and LAST_VALUE functions except the NTH_VALUE lets you find a specific position in the analytic window such as 2nd, 3rd, or 4th value.
Syntax
The syntax for the NTH_VALUE function in Oracle/PLSQL is:
NTH_VALUE (measure_column, n) [FROM FIRST | FROM LAST] [RESPECT NULLS | IGNORE NULLS] OVER ([query_partition_clause] [order_by_clause [windowing_clause]])
Parameters or Arguments
- measure_column
- The column or expression that you wish to return.
- n
- It is the nth value of measure_column in the analytic window that you wish to return.
- FROM FIRST | FROM LAST
- Optional. It determines whether the calculation starts at the first row of the analytic window or the last row of the analytic window. If this parameter is omitted, the default is FROM FIRST which starts at the first row.
- RESPECT NULLS | IGNORE NULLS
- Optional. It determines whether NULL values are included or ignored in the analytic window calculation. If this parameter is omitted, the default is RESPECT NULLS which includes NULL values.
- query_partition_clause
- Optional. It is used to partition the results into groups based on one or more expressions.
- order_by_clause
- Optional. It is used to order the data within each partition.
- windowing_clause
-
Optional. It determines the rows in the analytic window to evaluate and it is important that you use the correct windowing_clause or you could get unexpected results. It can be a value such as:
windowing_clause Description RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW Last row in the window changes as the current row changes (default) RANGE BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING First row in the window changes as the current row changes RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING All rows are included in the window, regardless of the current row
Returns
The NTH_VALUE function returns the nth value in an ordered set of values from an analytic window.
If there are less than n rows in the data source window, the NTH_VALUE function will return NULL.
If the parameter n is NULL, the NTH_VALUE function returns an error.
Applies To
The NTH_VALUE function can be used in the following versions of Oracle/PLSQL:
- Oracle 12c, Oracle 11g Release 2
DDL/DML for Examples
If you want to follow along with this tutorial, get the DDL to create the tables and the DML to populate the data. Then try the examples in your own database!
Example
Let's look at some Oracle NTH_VALUE function examples and explore how to use the NTH_VALUE function in Oracle/PLSQL.
Second Highest Value by Dept_id
In this NTH_VALUE example, we have a table called employees with the following data:
EMPLOYEE_ID LAST_NAME FIRST_NAME SALARY DEPT_ID ----------- --------- ---------- ------ ------- 1000 Jackson Joe 2000 10 2000 Smith Jane 3500 10 3000 Ferguson Samantha 1900 10 4000 Reynolds Allen 4000 20 5000 Anderson Paige 3250 20 6000 Johnson Derek 2750 20 7000 Nelson Sarah 5000 30 8000 Burke Russell 1500 30
Now let's demonstrate how the NTH_VALUE function works by selecting data from the employees table. To return the dept_id and the second highest salary for dept_id 10 and 20, enter the following SQL statement in Oracle:
SELECT DISTINCT dept_id, NTH_VALUE(salary,2) OVER (PARTITION BY dept_id ORDER BY salary DESC RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS "SECOND HIGHEST" FROM employees WHERE dept_id in (10,20) ORDER BY dept_id;
These are the results that you should see:
DEPT_ID SECOND HIGHEST ------- -------------- 10 2000 20 3250
In this example, the NTH_VALUE returns the 2nd salary value as specified by NTH_VALUE(salary,2)
. The analytic window will partition results by dept_id and order the data by salary in descending order as specified by PARTITION BY dept_id ORDER BY salary DESC
. The RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
windowing_clause is used to ensure that all rows are included regardless of the current row. If you did not include this windowing_clause in this example, you would get some unexpected results.
Second and Third Highest Salaries by Dept_id
Now, let's show you how to use the NTH_VALUE function to return the 2nd and 3rd highest salaries for dept_id 10 and 20.
Based on the same employees table, enter the following SQL statement:
SELECT DISTINCT dept_id, NTH_VALUE(salary,2) OVER (PARTITION BY dept_id ORDER BY salary DESC RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS "SECOND HIGHEST", NTH_VALUE(salary,3) OVER (PARTITION BY dept_id ORDER BY salary DESC RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS "THIRD HIGHEST" FROM employees WHERE dept_id in (10,20) ORDER BY dept_id;
These are the results that you should see:
DEPT_ID SECOND HIGHEST THIRD HIGHEST ------- -------------- ------------- 10 2000 1900 20 3250 2750
In this example, we have used the NTH_VALUE function multiple times to find different nth values in the employees table.
Second Lowest Salary for all Employees
Finally, let's use the NTH_VALUE function to return the 2nd lowest salary in the entire employees table. In this example, we won't require a query_partition_clause.
Based on the data in the employees table, enter the following SELECT statement:
SELECT DISTINCT NTH_VALUE(salary,2) OVER (ORDER BY salary ASC RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS "SECOND LOWEST" FROM employees;
These are the results that you should see:
SECOND LOWEST ------------- 1900
In this example, we have used the NTH_VALUE function to find the second lowest salary in the employees table and as such, sorted the salary in ascending order to properly order the data in the analytic window (as specified by ORDER BY salary ASC
).
And because we want the second lowest salary for the table (not based on a dept_id), we did not need to include query_partition_clause to partition the data.
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