Dynamic Data Masking (DDM) is a nifty way to keep sensitive data under wraps by showing a masked version to users who shouldn't see the real thing. It tweaks the data stream so that when someone asks for data, they get a disguised version instead of the actual sensitive info.

Now, Supabase doesn't come with built-in support for DDM. But don't worry, you can still set up a basic version using PostgreSQL views and Row Level Security (RLS).

A View in PostgreSQL is like a virtual table that you create based on a SELECT statement. By picking only the non-sensitive data in your SELECT statement, you make sure the View never shows anything sensitive. Here's a quick example of how to create a View:

CREATE VIEW public.non_sensitive_users AS
SELECT
    id,
    non_sensitive_column_1,
    non_sensitive_column_2
FROM
    users;

So, in this example, the View "non_sensitive_users" only includes id, non_sensitive_column_1, and non_sensitive_column_2 from the users table. Simple, right?

Row Level Security (RLS) in PostgreSQL lets you set up rules that control which rows a user can see or change when they run SELECT, UPDATE, or DELETE commands. This is super handy for keeping sensitive data out of sight.

First, you need to turn on RLS for your View:

ALTER TABLE public.non_sensitive_users ENABLE ROW LEVEL SECURITY;

Next, create a policy that only lets certain users or roles access the data:

CREATE POLICY non_sensitive_users_select_policy
ON public.non_sensitive_users
FOR SELECT 
USING (current_user = 'specified_role');

In this example, the policy only lets users with the role 'specified_role' see the data. Pretty neat, huh?

In your Supabase app, whenever you need to get user data, make sure your queries point to the non_sensitive_users view instead of the users table. This way, your app never pulls in sensitive data by accident.

By combining PostgreSQL Views and Row Level Security, you can set up a basic form of Dynamic Data Masking in your Supabase app. It's not a perfect solution, but it goes a long way in keeping sensitive data safe from prying eyes.