SELECT nurse FROM on_call WHERE blockfloor  =  1 AND blockcode  =  1
Find the ids of the nurses who are on call in block floor 1 and block code 1.
SELECT nurse FROM on_call WHERE blockfloor = 1 AND blockcode = 1
select nurse from on_call where blockfloor = value and blockcode = value
Find the ids of the nurses who are on call in block floor 1 and block code 1 .