Close, but no cigar    Double check your output, especially if you have duplicate X's in any of your datasets.   Data Merged_data Merge dataA(IN=fromdataA) dataB(IN=fromdataB) dataC(in=fromdataC) BY x; *Create indicator variables to show in which dataset the observation is present; SourceA=fromdataA; SourceB=fromdataB; SourceC=fromdataC; *keep only from A and B; if fromdataA AND fromdataB; run; ... View more

data _null_ tells SAS not to create a data set while executing this particular data step. There is no specific connection to the sleep function. You use a Data _null_ statement in this situation to pass commands to the system that you only want to execute once. Sleep tells it to pause between commands, usually as a safety precaution to wait for another process to finish. ... View more