## Wednesday, November 6, 2013

### Fun with SQL - My Birthday

This year is kind of fun, my birthday is on November 12th (next Tuesday, if you want to send gifts). That means it will fall on 11/12/13. Even better perhaps, katezilla's birthday is December 13th. 12/13/14. What does this have to do with SQL?

Someone mentioned to me last night that this wouldn't happen again for 990 years. I was thinking, "wow, I'm super special now (along with the other 1/365 * 6 billion people)!" Or am I? I had to do the math. Since date math is hard, and math is hard, and I'm good at neither, SQL to the rescue.

select
to_number( to_char( sysdate + ( rownum - 1 ), 'mm' ) ) month_of,
to_number( to_char( sysdate + ( rownum - 1 ), 'dd' ) ) day_of,
to_number( to_char( sysdate + ( rownum - 1 ), 'yy' ) ) year_of,
sysdate + ( rownum - 1 ) actual
from dual
connect by level <= 100000
(In case you were wondering, 100,000 days is just shy of 274 years. 273.972602739726027397260273972602739726 to be more precise.)

That query gives me this:
MONTH_OF DAY_OF YEAR_OF ACTUAL
-------- ------ ------- ----------
11       06     13      2013/11/06
11       07     13      2013/11/07
11       08     13      2013/11/08
11       09     13      2013/11/09
11       10     13      2013/11/10
11       11     13      2013/11/11
...
So how can I figure out where DAY_OF is equal to MONTH_OF + 1 and YEAR_OF is equal to DAY_OF + 1? In my head, I thought it would be far more complicated, but it's not.
select *
from
(
select
to_number( to_char( sysdate + ( rownum - 1 ), 'mm' ) ) month_of,
to_number( to_char( sysdate + ( rownum - 1 ), 'dd' ) ) day_of,
to_number( to_char( sysdate + ( rownum - 1 ), 'yy' ) ) year_of,
sysdate + ( rownum - 1 ) actual
from dual
connect by level <= 100000
)
where month_of + 1 = day_of
and day_of + 1 = year_of
order by actual asc
Which gives me:
MONTH_OF DAY_OF YEAR_OF ACTUAL
-------- ------ ------- ----------
11       12     13      2013/11/12
12       13     14      2014/12/13
01       02     03      2103/01/02
02       03     04      2104/02/03
03       04     05      2105/03/04
04       05     06      2106/04/05
05       06     07      2107/05/06
...
OK, so it looks closer to 100 years, not 990. Let's subtract. LAG to the rescue.
select
actual,
lag( actual, 1 ) over ( partition by 1 order by 2 ) previous_actual,
actual - ( lag( actual, 1 ) over ( partition by 1 order by 2 ) ) time_between
from
(
select
to_number( to_char( sysdate + ( rownum - 1 ), 'mm' ) ) month_of,
to_number( to_char( sysdate + ( rownum - 1 ), 'dd' ) ) day_of,
to_number( to_char( sysdate + ( rownum - 1 ), 'yy' ) ) year_of,
sysdate + ( rownum - 1 ) actual
from dual
connect by level <= 100000
)
where month_of + 1 = day_of
and day_of + 1 = year_of
order by actual asc
Which gives me:
ACTUAL     PREVIOUS_ACTUAL TIME_BETWEEN
---------- --------------- ------------
2013/11/12
2014/12/13                          396
2103/01/02                        32161
2104/02/03                          397
2105/03/04                          395
2106/04/05                          397
2107/05/06                          396
2108/06/07                          398
2109/07/08                          396
2110/08/09                          397
2111/09/10                          397
2112/10/11                          397
2113/11/12                          397
2114/12/13                          396
2203/01/02                        32161
So, it looks like every 88 years it occurs and is followed by 11 consecutive years of matching numbers. The next time 11/12/13 and 12/13/14 will appear is in 2113 and 2114. Yay for SQL!

Stew said...

Fun stuff! Happy birthday next Tuesday!

Kim Berg Hansen said...

Fun to play with dates. Consider:

01/02/xx03
02/03/xx04
...
11/12/xx13
12/13/xx14 <==

The last line is only valid in MM/DD/YYYY - not in DD/MM/YYYY.
So in this case americans have one extra such day compared to the standardized world, where a special date is where day is one less than month and not the other way around ;-)

PS.

December 13th is Saint Lucy's Day: http://en.wikipedia.org/wiki/Saint_Lucy's_Day

On that day there will be hundreds of Santa Lucia processions in Scandinavia with singing girls in white dresses holding candles. Like this one: http://www.youtube.com/watch?v=aqp6il_QVbA

Imagine they are all singing for Katezilla :-)

chet justice said...

Don't give me a hard time about America's peculiarities. :)

Posted to katezilla's timeline.

Jack Porter said...

This is great! I really like to try this out. I'll be sure to tell my friend about this. Thanks for sharing.

Tom Wurzbach said...

Nice. I love when things can be proven incorrect. One of my least favorite internet memes is the "this month has a blue moon and blue moons only occur once every bazillion years" or somesuch. They're just not that rare... And that, too, would be an interesting query.

Chris Hunt said...

No SQL required really.

If dates are presented m/d/y, d=m+1, y=m+2, and m is a number between 1 and 12, the only possible answers are:

01/02/03
02/03/04
03/04/05
04/05/06
05/06/07
06/07/08
07/08/09
08/09/10
09/10/11
10/11/12
11/12/13
12/13/14