On Thu, 26 Oct 2006 04:17:34 -0400, Gerhard Hellriegel <gerhard.hellriegel@T-ONLINE.DE> wrote:

>lavanya, >there is no update function in SAS as far as I know. >I think you mean the update statement, like: > >data a; > update a b; > by var; >run; > >that thing you use instead of SET. You need at least one common key variable >in a and b (the BY-list) and the other common variables in A are replaced by >the values in B. If all variables in B are also in A and also A is the ouput >dataset, SAS can optimize that step and make a real update in place. Both >must be sorted of course.

I believe that UPDATE will never change a data set in place. If you want that to happen, use MODIFY instead of UPDATE.

MODIFY does not require that all variables in B are also in A. Of course, any newly introduced variables are not preserved in the output. But consider, for example, a DATA step that is supposed to selectively delete observations from A. B might include a variable DELETE_FLAG to control that.

MODIFY does *not* require that either A or B be either sorted or indexed by the BY variables. In fact, sorting is a dubious proposition in this situation, since any new observations will be written to the end of A and this will generally destroy the sorted-by property. On the other hand, indexing A can dramatically improve performance.

>Regards, >Gerhard > > > >On Thu, 26 Oct 2006 00:42:59 -0700, lavanya <lavenskey@GMAIL.COM> wrote: > >>hi all!! >> >>can anyone pls tel me what is the update function in sas >> >> >>thank you, >> >>lavanya