PROC SQL - UPDATE WITHOUT OVERWRITING WITH MISSING VALUES

[kmcnulty]

I am trying to update a master table with a reference table but my reference table isn't perfect and I don't want it to overwrite my master table if it's missing some of the devices I need.  

I was thinking  when I submit the following code it wouldn't update my speeds in my master table if they weren't in my reference table but it seems to still set my master table values to missing if they are not in the reference table. Am I missing something?

proc sql;

update mastertable tableA

set speed = (select Speed

from referencetable

where (tableA.device = device and tablea.daydate between min_daydate AND max_daydate));

where device in(select device from referencetable);

quit;

[kmcnulty]

I was thinking  when I submit the following code it wouldn't update my speeds in my master table if they weren't in my reference table but it seems to still set my master table values to missing if they are not in the reference table. Am I missing something?

proc sql;

update mastertable tableA

set speed = (select Speed

from referencetable

where (tableA.device = device and tablea.daydate between min_daydate AND max_daydate));

where device in(select device from referencetable);

quit;

[kmcnulty · Accepted solution]

I figured it out!!!!

proc sql;

update mastertable tableA

set speed = case when device in (select device from referencetable) then (select Speed

from referencetable

where (tableA.device = device and tablea.daydate ge min_daydate and tablea.daydate lt max_daydate)) else speed end;

where device in (select device from referencetable);

quit;