inner join and outer join for multiple tables - UDB

I like to use inner join and outer join among multiple tables on UDB...
For this, I wrote below, but it basically picking up too many duplicated records. basically I do not like to have duplicated entry from orders_history, just add 4 external IDs from instrument_ext_ref for each types if exist, if not, just put NULL there.
Would you please let me know how I should restrict?
I've tried to use distinct but then sql doesn't return value, maybe looping....
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select * from orders_history o
   inner join instrument i
               on o.instrument_id = i.instrument_id
            and o.date_order between '20070201' and '20070228'
            and o.status = '3'
   left outer join instrument_ext_ref ref_1
            on o.instrument_id = ref_1.instrument_id
         AND ref_1.instrument_id IS NOT NULL
             and ref_1.ext_id_type = 'CUSIP'
   left outer join instrument_ext_ref ref_2
            on o.instrument_id = ref_2.instrument_id
         AND ref_2.instrument_id IS NOT NULL
             and ref_2.ext_id_type = 'SEDOL'
   left outer join instrument_ext_ref ref_3
            on o.instrument_id = ref_2.instrument_id
         AND ref_3.instrument_id IS NOT NULL
             and ref_3.ext_id_type = 'ISIN'
   left outer join instrument_ext_ref ref_4
            on o.instrument_id = ref_4.instrument_id
         AND ref_4.instrument_id IS NOT NULL
             and ref_4.ext_id_type = 'QUICK'
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