Queries with IN clauses that are pushing the optimizer to its limit

create table t1234 (

  campaignid varchar(32) not null,

  adgroupid varchar(32) not null,

  col1 int not null,

  PRIMARY KEY (campaignid,adgroupid),

  UNIQUE KEY adgroupid (adgroupid)

);

explain

select * from t1234

where 

   campaignid='Finland' AND adgroupid IN ('Lahti','Imatra')

   OR

   campaignid='Russia' AND adgroupid IN ('Petersburg', 'Moscow')

   OR 

   campaignid='Sweden' AND adgroupid IN ('Stockholm', 'Uppsala')

   OR 

   campaignid='Germany' AND adgroupid IN ('Berlin', 'Frankfurt')

   OR 

   campaignid='Belgium' AND adgroupid IN ('Brussels', 'Gent')

   OR 

   campaignid='Portugal' AND adgroupid IN ('Lisbon', 'Porto')

...