ROWNUM

ROWNUM is a pseudo-column that returns a row's position in a result set. ROWNUM is evaluated AFTER records are selected from the database and BEFORE the execution of ORDER BY clause.

The following type of queries will ALWAYS return NO DATA:

... WHERE ROWNUM > x
... WHERE ROWNUM BETWEEN x AND y
... WHERE ROWNUM IN (x, y, z, ...)

However, this will work:

... WHERE ROWNUM < x

This query will return ROWNUM values that are out of numerical order:

select ROWNUM, deptno from emp where  ROWNUM < 10
order  by deptno, ROWNUM;

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