Hier is hoe je het deed - alias in de kolomnaam
select
-- etc etc
(select innerDLI.datetime_created from distribution_line_items innerDLI where innerDLI.item_number = distribution_line_items.item_number order by innerDLI.datetime_created asc limit 1) as Origination,
-- etc etc
from distribution_stop_information
-- etc etc
Hier is hoe je het in de waar kunt plaatsen, alias in de join
select
-- etc etc
Origination.datetime_created
-- etc etc
from distribution_stop_information
left join distribution_line_items AS Origination ON Origination.item_number = distribution_line_items.item_number
where Origination.datetime_created > to_date(?, 'YYYY-MM-DD') - interval '180 days'
-- etc etc
Er is niets aan dit dat beter is dan de oplossing die je hebt gepost (de sql-optimizer zou in hetzelfde plan moeten resulteren) maar het is "een alias gebruiken in de waar-clausule"