我想您要一个城市，首先检查5位数的邮政编码，然后再检查3位数的邮政编码:

I am guessing that you want one city, first checking the 5-digit zip code and then the 3-digit one:

select mc.*, coalesce(zc5.city_name, zc3.city_name) as city_name
from main_cohort mc left join
     zip_code zc5
     on mc.zip_value5 = zc5.zip_code left join
     zip_code zc3
     on mc.zip_value3 = zc3.zip_code