Merge overwrite stopping at first match - merge

Question

i currently have three data sets in SAS 9.3
Data set "Main" contains SKU ID's and Customer ID's as well as various other variables such as week.
Customer_ID week var2 var3 SKU_ID
1 1 x x 1
1 2 x x 1
1 3 x x 1
1 1 x x 2
1 2 x x 2
2 1 x x 1
2 2 x x 1
2 3 x x 1
2 1 x x 2
2 2 x x 2
data set "standard" contains the standard location for each Customer_ID.
data set "overrides" contains data override location (if applicable) for a certain sku for certain customers for instance. Thus, it contains SKU_ID, customer_id and location
standard data set
customer_id location
1 A
1 A
2 C
2 C
override dataset
customer_id sku_id location
1 1 A
1 2 B
When merging all of the data sets this is what i get
Customer_ID week var2 var3 SKU_ID location
1 1 x x 1 A
1 2 x x 1 A
1 3 x x 1 A
1 1 x x 2 B
1 2 x x 2 A
2 1 x x 1 C
2 2 x x 1 C
2 3 x x 1 C
versus what i want it to look like
Customer_ID week var2 var3 SKU_ID location
1 1 x x 1 A
1 2 x x 1 A
1 3 x x 1 A
1 1 x x 2 B
1 2 x x 2 B
2 1 x x 1 C
2 2 x x 1 C
2 3 x x 1 C
proc sort data=overrides; by Location SKU_ID; run;
Proc sort data= main; by Location SKU_ID;
run;
Proc sort data= Standard; by Location;
run;
data Loc_Standard No_LOC;
Merge Main(in = a) Standard(in = b);
by Location;
if a and b then output Loc_standard;
else if b then output No_LOC;
run;
/*overwrites standard location if an override for a sku exist*/
Data Loc_w_overrides;
Merge Loc_standard overrides;
by Location SKU_ID;
run;

Answer 1

That is how SAS combines datasets. When datasets have observations to contribute to a BY group the values from the datasets are read in the order they appear in the MERGE statement. But when one dataset runs out of new observations for the BY group then SAS does not read those values in. So the value read from the other dataset is no longer replaced.
Either drop the original variable and just use the value from the second dataset. Basically this will setup an 1 to Many merge.
Or rename the override variable and add your own logic for when to apply the override.
I am not sure how you are getting the result you posted since you do not have any standards for CUSTOMER_ID=2 in your posted data. If the values of location to not depend on customer_id then why is that variable in the standards and override datasets?
Perhaps you meant that the standards dataset only has SKU_ID and location?
data main_w_standards;
merge main standards;
by sku_id ;
run;
proc sort data=main_w_standards;
by customer_id sku_id;
run;
data main_w_overrides;
merge main_w_standards overrides(in=in2 rename=(location=override));
by customer_id SKU_ID;
if in2 then location=override;
drop override;
run;

Answer 2

Why not UPDATE the STANDARD(loc) with OVERIDE(oride) and then merge with customer data.
data loc;
input customer_id Sku_id location:$1.;
cards;
1 1 A
1 2 A
;;;;
proc print;
data oride;
input customer_id sku_id location:$1.;
cards;
1 1 A
1 2 B
;;;;
run;
proc print;
data locoride;
update loc oride;
by cu: sk:;
run;