Thank you both. I will test it right away.

Hi,

You can add SQL constraints using a server action.

Example:

Steps:

1. Settings- > Technical -> Actions -> Server Action

Model: Sales Order

Type: Execute Code

Code:

env.cr.execute("""

    ALTER TABLE sale_order

    ADD CONSTRAINT unique_name UNIQUE (name)

""")

- unique_name = name of the constraint

- name = field

Hope it helps.

The answer you've commented on in https://www.odoo.com/forum/1/155133 already says what to do if you can't do it with a module - i.e. Odoo Online. You need to create an Automation Rule that is triggered On Update and On Create to check if other records with that value already exist. You can not use the Studio UI directly if this is what you're asking explicitly.

_sql_constraints = [] is python code you can not add directly.

Automation Rules are created, when in Developer Mode (https://www.odoo.com/documentation/18.0/applications/general/developer_mode.html), via Settings -> Technical --> Automation -> Automation Rules.