SQL Number increment

Question

I want a query that increment a number by one after each certain number of records...
example,
after 3 rows it increases a counter by 1
Counter Value
1 A
1 b
1 c
2 d
2 e
2 f
3 d
3 e
3 f

Answer 1

NTILE(3) will split all rows into three equal size (as close as possible) groups while OP asked to divide all rows into groups where each group has 3 rows. All you need for that is ROWNUM. See the difference:
SQL> select ename,NTILE(3) OVER(ORDER BY ename) from emp;
ENAME      NTILE(3)OVER(ORDERBYENAME)
ADAMS                               1
ALLEN                               1
BLAKE                               1
CLARK                               1
FORD                                1
JAMES                               2
JONES                               2
KING                                2
MARTIN                              2
MILLER                              2
SCOTT                               3
ENAME      NTILE(3)OVER(ORDERBYENAME)
SMITH                               3
TURNER                              3
WARD                                3
14 rows selected.
SQL> select ename,ceil(rownum / 3) from emp;
ENAME      CEIL(ROWNUM/3)
MILLER                  1
CLARK                   1
KING                    1
ADAMS                   2
SMITH                   2
JONES                   2
FORD                    3
SCOTT                   3
JAMES                   3
MARTIN                  4
WARD                    4
ENAME      CEIL(ROWNUM/3)
ALLEN                   4
BLAKE                   5
TURNER                  5
14 rows selected.
SQL> SY.