SAS : Many to Many Merge

Let's take an example -

SAS - Many-to-many merge

The DATA step does not handle many-to-many matching very well. When we perform many to many merges. the result should be a cartesian (cross) product. For example, if there are three records that match from one contributing data set to two records from the other, the resulting data set should have 3 × 2 = 6 records.

MERGE does not create a cartesian product incase of a many-to-many relationship.It will create number of records for a duplicate value equal to maximum in both the table.

SAS Code - 

data dat1;

input ID Info;

cards ;

1 3123

1 1234

2 7482

2 8912

3 1284

;

run;

data dat2;

input ID Info2;

cards ;

1 4444

1 5555

1 8989

2 9099

2 8888

3 8989

;

run;

data combined;

merge dat1 dat2 ;

by ID;

run;

Output : Merge

PROC SQL
PROC SQL creates a cartesian product incase of a many-to-many relationship. 

proc sql noprint;
create table combined2 as
select * from dat1 a
left join dat2 b
on a.ID = b.ID;
quit;

The output would be same as shown in the first image - "Cross Product".