利用SQL查找表中的质数(prime number)和完全数(perfect number)以及几个有趣的SQL语句

之前在某次interview中被老外问到如何用SQL找出列上的质数和完全数的问题；我当时已经多年没有写过这种考算法和SQL技巧(纯粹的技巧)的语句了，乍遇此问题倒是有些棘手。现在录以记之，供人参考.

SQL> create table numbers(NO int) ;

表已创建。

SQL> insert into numbers  select rownum  from dba_objects;

已创建71937行。

SQL> commit;

提交完成。

SELECT X.NO as Primes  /*查找质数(find prime number)*/
FROM Numbers N
CROSS JOIN Numbers X
WHERE mod(X.NO, N.NO) != 0
AND N.NO < X.NO
GROUP BY X.NO
HAVING(X.NO - Count(*)) = 2;

PRIMES
---------
4931
4919
4909
4903
4889
4877
4871
4861
4831
4817
4813 ................

SELECT X.no as Perfect /*查找完全数,find perfect nober*/
FROM numbers N
CROSS JOIN numbers X
WHERE mod(X.no, N.no) = 0
and X.no > 1
AND N.no < X.no
AND N.no > 0
GROUP BY X.no
HAVING SUM(N.no) = X.no;

PERFECT
----------
6
28
496

......................

附:

select ltrim(sys_connect_by_path(rownum || '*' || lv || '=' ||  /* SQL_99乘法口诀表*/
rpad(rownum * lv, 2),
'  '))
from (select level lv from dual connect by level < 10)
where lv = 1
connect by lv + 1 = prior lv;

1*1=1
2*2=4   2*1=2
3*3=9   3*2=6   3*1=3
4*4=16  4*3=12  4*2=8   4*1=4
5*5=25  5*4=20  5*3=15  5*2=10  5*1=5
6*6=36  6*5=30  6*4=24  6*3=18  6*2=12  6*1=6
7*7=49  7*6=42  7*5=35  7*4=28  7*3=21  7*2=14  7*1=7
8*8=64  8*7=56  8*6=48  8*5=40  8*4=32  8*3=24  8*2=16  8*1=8
9*9=81  9*8=72  9*7=63  9*6=54  9*5=45  9*4=36  9*3=27  9*2=18  9*1=9

with a as
(select distinct round(a.x + b.x) x, round(a.y + b.y) y
from (select (sum(x) over(order by n)) x,
round(sum(y) over(order by n)) y
from (select n,
cos(n / 30 * 3.1415926) * 2 x,
sin(n / 30 * 3.1415926) y
from (select rownum - 1 n
from all_objects
where rownum <= 30 + 30))) a,
(select n,
(sum(x) over(order by n)) x,
round(sum(y) over(order by n)) y
from (select n,
cos(m / 3 * 3.1415926) * 2 * 15 x,
sin(m / 3 * 3.1415926) * 15 y
from (select case
when rownum <= 2 then
3
when rownum = 3 then
-2
else
-6
end m,
rownum - 1 n
from all_objects
where rownum <= 5))) b)
select replace (sys_connect_by_path(point, '/'), '/', null) star  /*SQL 绘制奥运五环*/
from (select b.y, b.x, decode(a.x, null, ' ', '*') point
from a,
(select *
from (select rownum - 1 + (select min(x) from a) x
from all_objects
where rownum <= (select max(x) - min(x) + 1 from a)),
(select rownum - 1 + (select min(y) from a) y
from all_objects
where rownum <= (select max(y) - min(y) + 1 from a))) b
where a.x(+) = b.x
and a.y(+) = b.y)
where x = (select max(x) from a)
start with x = (select min(x) from a)
connect by y = prior y and x = prior x + 1;

with a as                                             /*sql 绘制五角星*/
(select distinct round(sum(x) over(order by n)) x,
round(sum(y) over(order by n)) y
from (select n,
cos(trunc(n / 20) * (1 - 1 / 5) * 3.1415926) * 2 x,
sin(trunc(n / 20) * (1 - 1 / 5) * 3.1415926) y
from (select rownum - 1 n from all_objects where rownum <= 20 * 5)))
select replace (sys_connect_by_path(point, '/'), '/', null) star
from (select b.y, b.x, decode(a.x, null, ' ', '*') point
from a,
(select *
from (select rownum - 1 + (select min(x) from a) x
from all_objects
where rownum <= (select max(x) - min(x) + 1 from a)),
(select rownum - 1 + (select min(y) from a) y
from all_objects
where rownum <= (select max(y) - min(y) + 1 from a))) b
where a.x(+) = b.x
and a.y(+) = b.y)
where x = (select max(x) from a)
start with x = (select min(x) from a)
connect by y = prior y and x = prior x + 1;

SELECT LPAD(MONTH, 20 - (20 - LENGTH(MONTH)) / 2) MONTH,      /*sql绘制年历*/
       "Sun",
       "Mon",
       "Tue",
       "Wed",
       "Thu",
       "Fri",
       "Sat"
  FROM (SELECT TO_CHAR(dt, 'fmMonthfm YYYY') MONTH,
               TO_CHAR(dt + 1, 'iw') week,
               MAX(DECODE(TO_CHAR(dt, 'd'),
                          '1',
                          LPAD(TO_CHAR(dt, 'fmdd'), 2))) "Sun",
               MAX(DECODE(TO_CHAR(dt, 'd'),
                          '2',
                          LPAD(TO_CHAR(dt, 'fmdd'), 2))) "Mon",
               MAX(DECODE(TO_CHAR(dt, 'd'),
                          '3',
                          LPAD(TO_CHAR(dt, 'fmdd'), 2))) "Tue",
               MAX(DECODE(TO_CHAR(dt, 'd'),
                          '4',
                          LPAD(TO_CHAR(dt, 'fmdd'), 2))) "Wed",
               MAX(DECODE(TO_CHAR(dt, 'd'),
                          '5',
                          LPAD(TO_CHAR(dt, 'fmdd'), 2))) "Thu",
               MAX(DECODE(TO_CHAR(dt, 'd'),
                          '6',
                          LPAD(TO_CHAR(dt, 'fmdd'), 2))) "Fri",
               MAX(DECODE(TO_CHAR(dt, 'd'),
                          '7',
                          LPAD(TO_CHAR(dt, 'fmdd'), 2))) "Sat"
          FROM (SELECT TRUNC(SYSDATE, 'y') - 1 + ROWNUM dt
                  FROM all_objects
                 WHERE ROWNUM <= ADD_MONTHS(TRUNC(SYSDATE, 'y'), 12) -
                       TRUNC(SYSDATE, 'y'))
         GROUP BY TO_CHAR(dt, 'fmMonthfm YYYY'), TO_CHAR(dt + 1, 'iw'))
 ORDER BY TO_DATE(MONTH, 'Month YYYY'), TO_NUMBER(week);

   	MONTH	Sun	Mon	Tue	Wed	Thu	Fri	Sat
1	     1月 2010	 3	 4	 5	 6	 7	 8	 9
2	     1月 2010	10	11	12	13	14	15	16