Merging Data Sets Faster

When merging two SAS data sets, many of us use one of these two methods to keep only the observations where both input data sets contribute:

data test1;
merge step1(in=a)
step2(in=b);
by district studentid;
if a=1 and b=1;
run;
or
data test1;
merge step1(in=a)
step2(in=b);
by district studentid;
if a and b;
run;

This method executes faster (and saves a few keystrokes):
data test1;
merge step1(in=a)
step2(in=b);
by district studentid;
if a*b;
run;

This shortened version of the IF statement works since if either the variable a or b is false, the expression resolves to zero (false).