with forupdate as (
    select ci.client_id, ci.client_firstname, ci.client_lastname, ci.client_email, ci.client_phone, ci.client_city, ci.age,
        case
            when c.age is null then 'I'
        else 'U'
        end as "action"
    fROM
        clients_inc as ci
        left join clients as c
        on ci.client_id = c.client_id
        and (ci.client_firstname <> c.client_firstname
        or ci.client_lastname <> c.client_lastname
        or ci.client_email <> c.client_email
        or ci.client_phone <> c.client_phone
        or ci.client_city <> c.client_city
        or ci.age <> c.age))

update clients
set
    client_firstname = forupdate.client_firstname,
    client_lastname = forupdate.client_lastname,
    client_email = forupdate.client_email,
    client_phone = forupdate.client_phone,
    client_city = forupdate.client_city,
    age = forupdate.age
from
    clients c
    inner join
    forupdate
    on c.client_id = forupdate.client_id
where c.client_id = forupdate.client_id and "action" = 'U';