proc SQL order by a negative date column?

[CharlieSong]

Hi,

Can a order by followed by a negative date column?

I have a code copied from somewhere like

PROC SQL;
	CREATE TABLE mcapData AS
	SELECT a.permno,
	a.date,
	a.mcap
	FROM retData AS a
	ORDER BY a.permno,
	-a.date;
	QUIT;

Is that a negative sign or just some error?

[PGStats]

It is just a trick which should be written

BY a,permno, a.date DESC;

[CharlieSong]

Thanks! You mean I can write like that but better use DESC?

[PGStats]

DESC states what you want more clearly. The next person looking at the query will not wonder what you really meant to do.

[CharlieSong]

Could you tell me whether SAS allows to use like that? 

[PGStats]

Yes, you can ORDER BY a SQL expression. Check the Documentation.

[PGStats]

Added explanation. SAS dates are just numbers. Under the hood, the date 01JAN2010 is just 18263. So -date is also just a number; -18263 when viewed as a date is 31DEC1909. When SAS is sorting by a SAS date, it is in fact just sorting numbers.

Hope this helps.

[CharlieSong]

Hi,Thank you very much ! I understand it now.