ROW_NUMBER in PostgreSQL
ROW_NUMBER is a window function that assigns an unique integer value (which starts with one and increments by one) to each row in a result set.
ROW_NUMBER() OVER( [PARTITION BY column_1, column_2,…] [ORDER BY column_3,column_4,…] )
ROW_NUMBER() operates on a set of rows called a window.
PARTITION BY clause splits this window into smaller subsets (i.e. partitions); if omitted,
ROW_NUMBER() will treat the entire window as a single partition.
ORDER BY inside
OVER determines the order in which the numbers are assigned.
DISTINCT in conjugtion with
ROW_NUMBER, it's important to remember that
ROW_NUMBER() operates on the result set before the
DISTINCT is applied, i.e. instead of this query
SELECT DISTINCT salary, ROW_NUMBER () OVER (ORDER BY salary) FROM employees ORDER BY salary;
use this query
WITH salaries AS ( SELECT DISTINCT salary FROM employees ) SELECT salary, ROW_NUMBER () OVER (ORDER BY salary) FROM salaries;
ROW_NUMBER() can be used for pagination.
SELECT * FROM ( SELECT *, ROW_NUMBER () OVER (ORDER BY name) FROM employees ) x WHERE ROW_NUMBER BETWEEN 7 AND 13;
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