full outer join on two keys - sql

Question

I am trying to do merge two tables on phone numbers so that if I find phone in either of the tables then join the rest of the fields as shown below.
Now there are scenarios where phone doesn't exist in both the tables. Then the table should join on email_id, so basically first check if phone matches if not then check for email id match. If none then drop the record.
select COALESCE(icici.phone, hsbc.phone) as phone,
COALESCE(icici.email_id, hsbc.email_id) as email_id, city
from credit_card.icici
full outer join credit_card.hsbc on icici.phone = hsbc.phone
or icici.email_id = hsbc.email_id
limit 10
But I am getting this error
ERROR: FULL JOIN is only supported with merge-joinable or hash-joinable join conditions
SQL state: 0A000
Is there a way to solve it, or is there a better way to do this?

Answer 1

You can union the result of a left and a right join:
SELECT COALESCE(icici.phone, hsbc.phone) as phone,
COALESCE(icici.email_id, hsbc.email_id) as email_id, city
FROM credit_card.icici
LEFT OUTER JOIN credit_card.hsbc on icici.phone = hsbc.phone
OR icici.email_id = hsbc.email_id
UNION (
SELECT COALESCE(icici.phone, hsbc.phone) as phone,
COALESCE(icici.email_id, hsbc.email_id) as email_id, city
FROM credit_card.icici
RIGHT OUTER JOIN credit_card.hsbc on icici.phone = hsbc.phone
OR icici.email_id = hsbc.email_id
WHERE icici.id IS NULL
)
However, the right join may only contain the rows that were not found for any values from the left table. These rows are filtered out using WHERE, for example, by checking the primary key for NULL.

Answer 2

Use union all and aggregation:
select phone, max(email_id)
maxCOALESCE(icici.phone, hsbc.phone) as phone,
COALESCE(icici.email_id, hsbc.email_id) as email_id, city
from ((select phone, email_id
from credit_card.icici
) union all
(select phone, email_id
from credit_card.hsbc
)
) cc
group by phone,
(case when phone is null then email_id end);