Delete a specific column only not the rows

Question

Hi below is my select statement
select b.*
from alco_external_key b
inner join alco_user as a
on  a.user_id = b.bob_id
where b.external_key = '025'
and it displays 3 columns (empID,emp_external_id,external_key)
is there a way to only delete the value of the exernal_key column that is 025 not the whole row
Thank You

Answer 1

Use update instead:
Update b
Set external_key=null
from alco_external_key b
inner join alco_user as a
on a.user_id = b.bob_id
where b.external_key = '025'
--Or
Merge alco_external_key b
using alco_user as a
on a.user_id = b.bob_id
When matched and b.external_key = '025' then
Update
Set Set external_key=null;