topic Re: Why does SAS change the where-clause conjugates? in SAS Programming

Why does SAS change the where-clause conjugates?

sh0e — Wed, 29 Jun 2016 16:44:51 GMT

I have noticed that if my where clause looks something like this:

not( missing( ben_per_start_date ) | missing( ben_per_end_date ) )

SAS turns it into this logical equivalence

(not MISSING(ben_per_start_date)) and (not MISSING(ben_per_end_date)

Does this mean that I am coding my original incorrectly or inefficiently?

- Jack

Re: Why does SAS change the where-clause conjugates?

PGStats — Wed, 29 Jun 2016 17:46:57 GMT

What evidence do you have that it is doing that?

Re: Why does SAS change the where-clause conjugates?

sh0e — Wed, 29 Jun 2016 17:56:04 GMT

That's what I posted.

The first piece of code is from the submitted SAS code.

The second piece of code was lifted from the SAS log.

Sorry if that wasn't clear.

Re: Why does SAS change the where-clause conjugates?

PGStats — Wed, 29 Jun 2016 18:12:50 GMT

For some obscure reason, SAS/SQL is very poor at handling OR operations. So, I guess it prefers the logical AND equivalent. Since both are logically equivalent, you should use the version that's clearer to you.

Re: Why does SAS change the where-clause conjugates?

Kurt_Bremser — Wed, 29 Jun 2016 19:26:35 GMT

When you have an and instead of an or, you can shortcut the condition when the first part is false. This reduces the overall amount of comparisons that must be made.

Re: Why does SAS change the where-clause conjugates?

sh0e — Wed, 29 Jun 2016 19:33:21 GMT

@Kurt_Bremser Are you writing that there are fewer comparisons using the AND operator because in the first expression is false, the second is not evaluated?

Re: Why does SAS change the where-clause conjugates?

PGStats — Wed, 29 Jun 2016 19:36:13 GMT

You could say the same thing of an OR operation. If the first operand is true, the second one doesn't need to be evaluated.