Описание тега rownum

ROWNUM is a pseudocolumn available in Oracle database. A pseudocolumn behaves like a table column, but is not actually stored in the table.

Questions tagged rownum should also be tagged oracle.

ROWNUM returns a number indicating the order in which rows have been returned from a select statement. The first row selected has a ROWNUM of 1, the second of 2 etc.

ROWNUM can be used to restrict the rows returned from a select statement but it's important to note that an ORDER BY is evaluated after the WHERE clause.

This select statement will return a random 10 rows:

select *
  from a_table
 where rownum < 11
 order by id asc

whereas this will return the first 10 IDs (a top-10 query):

select *
  from ( select *
           from a_table
          order by id asc )
 where rownum < 11

Oracle database documentation:

• ROWNUM Pseudocolumn

• Pseudocolumns

• On ROWNUM and Limiting Results by Tom Kyte in Oracle Magazine

Frequently asked Stackru questions:

• Selecting the second row of a table using rownum