Extracting data from the view to retrieve the foreign key is not declared

Given a view, I need to extract tables, the join columns (ON) . I need to do
this analysis because of the view (agreements with the join condition and
where) I can say that there is a foreign key

Example:

CREATE OR REPLACE VIEW x_customer AS
SELECT a.asset_id, a.client_id
FROM asset_d ad, asset a ON asset_id = ad.asset_id

Result:

NAMEVIEW |TABLE1 | COLUMN1 | TABLE2 | COLUMN2
x_customer| asset_d | asset_id | asset | asset_id |
x_customer| asset | - | - | - |

OR

CREATE OR REPLACE VIEW x_customer AS
SELECT a.asset_id, a.client_id, a.org_id, a.isactive, a.created,
a.createdby, a.updated, a.updatedby, a.value, a.name, a.description,
a.ad_user_id, ( SELECT count(*) AS count
FROM asset_d ad
WHERE a.asset_id = ad.asset_id) AS deliverycount
FROM asset a
WHERE a.bpartner_id IS NOT NULL;
Result:

NAMEVIEW |TABLE1 | COLUMN1 | TABLE2 | COLUMN2
x_customer| asset_d | asset_id | asset | asset_id |

Someone can help me?
Thanks

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