join two cases to create a new field - sql

Question

I have a table with fields man_phone and head_phone, and in the selects there are such cases for obtaining them:
case
when p.dep_code <> 'MM' then
case
when p.man_id = '%%%%%%%' then
'Man Spec-100'
when m.man_l is not null then
m.man_phone
else
case
when m2.man_l is not null then
m2.man_phone
else
m3.man_phone
end
end
else
o.cont_phone
end as man_phone,
case
when p.dep_code <> 'MM' then
case
when p.man_id = '%%%%%%%' then
'Man Spec-100'
when m2.man_l is not null then
m2.man_phone
else
m3.man_phone
end
else
o.head_phone
end as head_phone
I want to add a new field called head_login with a case if man_phone = head_phone, then it will output man_l as head_login and I tried to push these two existing cases into only one case, what would be the right way to do this?
case
case
when p.dep_code <> 'MM' then
case
when p.man_id = '%%%%%%%' then
'Man Spec-100'
when m.man_l is not null then
m.man_phone
else
case
when m2.man_l is not null then
m2.man_phone
else
m3.man_phone
end
end
else
o.cont_phone
end as man_phone,
case
when p.dep_code <> 'MM' then
case
when p.man_id = '%%%%%%%' then
'Man Spec-100'
when m2.man_l is not null then
m2.man_phone
else
m3.man_phone
end
else
o.head_phone
end as head_phone
when p.department_code <> 'MM' then
case
when man_phone = head_phone
m2.man_l
else
m3.man_l
end
end as head_login

Answer 1

I want to add a new field called head_login with a case if man_phone = head_phone, then it will output man_l as head_login and I tried to push these two existing cases into only one case.
Do not try to merge the two cases into a third case. Evaluate them in a sub-query and then put the CASE which compares them into an outer query:
SELECT man_phone,
head_phone,
CASE
WHEN man_phone = head_phone
THEN man_l2
ELSE man_l3
END AS head_login
FROM (
SELECT CASE <your case> END AS man_phone,
CASE <your case> END AS head_phone,
m2.man_l AS man_l2,
m3.man_l AS man_l3
FROM table_name
)