merge

These should be common sense about merge for a sas programmer. I need refresh my knowledge here.
“REPEAT OF BY-VALUES"

When there is a repetition of BY values in more than one data set, SAS switches to ‘one to one merging’,i.e. it steps through all data sets one observation at the time and matches them. When the last observation of that particular BY value is reached for a data set, it will be used further until it has been matched to the remainder of the observations for that BY group in the other data set(s).