Why Rownum is used?

Question

You can use ROWNUM to limit the number of rows returned by a query, as in this example: SELECT * FROM employees WHERE ROWNUM < 10; If an ORDER BY clause follows ROWNUM in the same query, then the rows will be reordered by the ORDER BY clause. The results can vary depending on the way the rows are accessed.

What is the Rownum?

For each row returned by a query, the ROWNUM pseudocolumn returns a number indicating the order in which Oracle selects the row from a table or set of joined rows. The first row selected has a ROWNUM of 1, the second has 2, and so on.

How is Rownum assigned?

ROWNUM is a pseudocolumn (not a real column) that is available in a query. ROWNUM will be assigned the numbers 1, 2, 3, 4, ... N , where N is the number of rows in the set ROWNUM is used with. A ROWNUM value is not assigned permanently to a row (this is a common misconception).

What is difference between Rownum and ROW_NUMBER?

ROWNUM is a pseudocolumn and has no parameters. ROW_NUMBER is an analytical function which takes parameters. ROWNUM is calculated on all results but before the ORDER BY. ROW_NUMBER is calculated as part of the column calculation.

Why row number is used in SQL?

ROW_NUMBER function is a SQL ranking function that assigns a sequential rank number to each new record in a partition. When the SQL Server ROW NUMBER function detects two identical values in the same partition, it assigns different rank numbers to both.

Expert · Answer