ROW_NUMBER
Purpose
Returns the sequential row number, where the first row is number one, of the row within its window partition according to the window ordering of the window.
Type
ANSI SQL:2011 window function.
Syntax
where:
|
Syntax element … |
Specifies … |
|
OVER |
the window partition and ordering. |
|
PARTITION BY |
the column, or columns, according to which the result set is partitioned. PARTITION BY is optional. If there are no PARTITION BY or RESET WHEN clauses, then the entire result set, specified by the ORDER BY clause, constitutes a partition. PARTITION BY clause is also called the window partition clause. |
|
ORDER BY |
in its value_expression the order in which to sort the values in the partition. |
|
ASC |
that the results are to be ordered in ascending sort order. If the sort field is a character string, the system orders it in ascending order according to the definition of the collation sequence for the current session. The default order is ASC. |
|
DESC |
that the results are to be ordered in descending sort order. If the sort field is a character string, the system orders it in descending order according to the definition of the collation sequence for the current session. |
|
NULLS FIRST |
that NULL results are to be listed first. |
|
NULLS LAST |
that NULL results are to be listed last. |
|
RESET WHEN |
the group or partition over which the function operates, depending on the evaluation of the specified condition. If the condition evaluates to TRUE, a new dynamic partition is created inside the specified window partition. RESET WHEN is optional. If there are no RESET WHEN or PARTITION BY clauses, then the entire result set constitutes a single partition. If RESET WHEN is specified, then the ORDER BY clause must be specified also. |
|
condition |
a conditional expression used to determine conditional partitioning. The condition in the RESET WHEN clause is equivalent in scope to the condition in a QUALIFY clause with the additional constraint that nested ordered analytical functions cannot specify a RESET WHEN clause. In addition, you cannot specify SELECT as a nested subquery within the condition. The condition is applied to the rows in all designated window partitions to create sub-partitions within the particular window partitions. For more information, see “RESET WHEN Condition Rules” on page 980 and the “QUALIFY Clause” in SQL Data Manipulation Language. |
ANSI Compliance
This is ANSI SQL:2011 compliant.
The RESET WHEN clause is a Teradata extension to the ANSI SQL standard.
Window Aggregate Equivalent
ROW_NUMBER() OVER (PARTITION BY column ORDER BY value)
is equivalent to
COUNT(*) OVER (PARTITION BY column ORDER BY value
ROWS UNBOUNDED PRECEDING).
For more information on COUNT, see “Window Aggregate Functions” on page 984.
Example
To order salespersons based on sales within a sales region, the following SQL query might yield the following results.
SELECT ROW_NUMBER() OVER (PARTITION BY sales_region
ORDER BY sales_amount DESC),
sales_person, sales_region, sales_amount
FROM sales_table;
Row_Number() sales_person sales_region sales_amount
------------ ------------ ------------ ------------
1 Baker East 100
2 Edwards East 99
3 Davis East 89
4 Adams East 75
1 Garabaldi West 100
2 Connors West 99
3 Fine West 99