Merge and Full join

[SASPhile]

I used the following two methods and found out there is difference in number of records for each method:

data x;

merge SASDATA.TU_LAIDC_APAC(in=a) SASDATA.TU_LAIDC_APAC_corp(in=b);

by id;

if a or b;

run;

The above results in 154718 records.

when I use the following:

proc sql;

create table xx as

select  coalesce(a.id,b.id) as id

from SASDATA.TU_LAIDC_APAC a  full outer join SASDATA.TU_LAIDC_APAC_corp b

on a.id=b.id;

quit;

This one results in 155047 records.

where could be the difference?

[Paul_Kent_SAS · Accepted solution]

you probably have some id va.uess with 2 or more rows in both datasets. suppose you have id=99 twice in both datasets - SQL will form the cartesian join of these (4 output records).  datastep will advance  each by group until the end of the shorter one, and then hold that row until the end of the longer one (2 output records)