what is a rownum in sql
The information in a ROWID gives Oracle everything he needs to find your row, the disk number, the cylinder, block and offset into the block. The ROWNUM is a pseudo-column, a placeholder that you can reference in SQL*Plus. The ROWNUM can be used to write specialized SQL and tune SQL. In sum, the difference between ROWNUM and ROWID is that ROWNUM is temporary while ROWID is permanent.