Among the orders made by customers in Germany, which one of them has the highest priority in delivery? Please give its order key.
orders refer to o_orderkey; Germany is the name of the nation which refers to n_name = 'GERMANY'; earlier orderdate have higher priority in delivery therefore MIN(o_orderdate);
SELECT T3.o_orderkey FROM nation AS T1 INNER JOIN customer AS T2 ON T1.n_nationkey = T2.c_nationkey INNER JOIN orders AS T3 ON T2.c_custkey = T3.o_custkey WHERE T1.n_name = 'GERMANY' ORDER BY T3.o_orderdate LIMIT 1