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update test set qty = qty - 1 where (location,sku,valid_date) 
in (select location,sku,min(valid_date) from test
where location = 'chuwei' and item_code = '5678' group by location,sku)
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Execute Immediate :as_sql Using atran_ex

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update test 
set qty = qty - 1 
from test t where valid_date = 
(select min(valid_date) from test where location = t.location and sku = t.sku)

update test 
set qty = qty - 1 
from test t where not exists 
(select 1 from test where location = t.location and sku = t.sku and valid_date < t.valid_date)

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update test set qty = qty - 1 
where item_code = '5678' 
and valid_date=(
select min(valid_date) from test a
where a.location= location and a.sku=sku )
)