How does one select EVERY Nth row from a table?

One can easily select all even, odd, or Nth rows from a table using SQL queries like this:

Method 1: Using a subquery


SELECT *
FROM emp
WHERE (ROWID,0) IN (SELECT ROWID, MOD(ROWNUM,4)
FROM emp);


Method 2: Use dynamic views (available from Oracle7.2):


SELECT *
FROM ( SELECT rownum rn, empno, ename
FROM emp
) temp
WHERE MOD(temp.ROWNUM,4) = 0;


Method 3: Using GROUP BY and HAVING


SELECT rownum, f1 FROM t1
GROUP BY rownum, f1 HAVING MOD(rownum,n) = 0 OR rownum = 2-n;


Please note, there is no explicit row order in a relational database. However, these queries are quite fun and may even help in the odd situation