Supabase JOIN: Connect Auth and Users Tables

Hey there, Supabase enthusiasts! Ever found yourself needing to link up your custom user data with the built-in authentication users table? You know, like when you’ve got a profiles table where you store extra goodies about your users – their avatars, bios, or maybe some super-secret user settings – and you want to easily grab all that info alongside their authentication details?

Well, you’re in luck, guys! Supabase makes this super straightforward with the power of SQL JOIN operations. It’s like giving your database superpowers to stitch together related pieces of information, making your data retrieval way more efficient and your app logic cleaner. Let’s dive deep into how you can master this technique and make your Supabase applications sing!

Understanding the Supabase Auth Users Table

First off, let’s get cozy with the auth.users table. This is the heart of Supabase’s authentication system. When someone signs up or logs in to your app, Supabase automatically creates a record for them in this table. It stores essential information like their unique user ID ( id ), email address ( email ), phone number ( phone ), and their authentication status ( confirmed_at , email_confirmed_at , etc.). Think of it as the master list of everyone who has access to your app.

This table is crucial because it’s the single source of truth for user identity and access. Every other piece of user-related data in your database should ideally be linked back to a user’s id from this table. This relational integrity is key to building a robust and secure application. For instance, if you have a posts table, each post would have a user_id column that references the id in auth.users . This way, you always know who authored which post.

Now, the auth.users table itself doesn’t hold your custom user profiles. That’s where your own tables come in. Supabase gives you the freedom to design your database schema exactly how you need it, and that includes creating tables to store additional user information. This separation is a good practice because it keeps the core authentication data lean and focused, while allowing you to expand your user profiles with whatever details are relevant to your specific application. For example, a social media app might need tables for user-uploaded photos, friends lists, and private messages, all linked back to the auth.users table. A project management tool might have tables for user roles, team assignments, and task priorities.

It’s important to remember that direct manipulation of the auth schema tables is generally discouraged. Supabase provides robust APIs and client-side SDKs to handle authentication operations. However, for querying and joining data, SQL becomes your best friend. Understanding the structure of auth.users and how to relate it to your own tables is the first step towards building powerful, data-rich applications on Supabase. The id column in auth.users is a UUID (Universally Unique Identifier), which is a standard and highly recommended way to ensure unique primary keys across distributed systems. When you create a foreign key in your custom tables to link to auth.users , you’ll typically be referencing this id column. This ensures that every piece of associated data is tied to a valid, existing user account.

Creating Your Custom User Profile Table

Alright, so you’ve got your auth.users table handling the heavy lifting of authentication. Now, let’s talk about building out your custom user profile table. This is where you get to store all that juicy extra information that makes each user unique in your app. Think of things like a user’s display name, their profile picture, a short bio, their website link, or maybe even their preferred theme settings. The possibilities are endless, guys!

Let’s say you decide to call your custom table profiles . It’s a pretty common and descriptive name, right? Inside this profiles table, you’ll need a few key columns. The most important one, and the linchpin that connects this table to auth.users , is a column that holds the user’s ID. This column should be of the same data type as the id column in auth.users , which is typically a uuid . Let’s call this column id as well, or perhaps user_id to be super explicit, though many developers opt for just id for simplicity when it’s the primary key of this related table and clearly references the auth user.

So, your profiles table might look something like this:

• id (uuid, Primary Key): This unique identifier will correspond directly to the id of a user in the auth.users table. When you create a new user through Supabase auth, you’ll typically create a corresponding row in your profiles table and populate this id column with the new user’s UUID. This is the magic link!
• avatar_url (text, nullable): Stores the URL to the user’s profile picture. It’s nullable because not everyone might upload one.
• full_name (text, nullable): The user’s full name, which they might provide upon signup or later.
• bio (text, nullable): A short description or bio for their profile.
• website (text, nullable): A link to their personal website or social media profile.
• created_at (timestamp with time zone, default now()): Tracks when the profile was created. Supabase often handles this automatically.
• updated_at (timestamp with time zone, default now()): Tracks the last time the profile was updated. You might set this up with a trigger.

When you set up the relationship between profiles.id and auth.users.id , you’ll typically define a foreign key constraint . This ensures data integrity. It means you can’t have a profile record without a corresponding user in auth.users , and if a user is deleted from auth.users , you can decide whether to cascade the deletion to the profiles table (though this should be done with extreme caution!). In Supabase’s SQL Editor, you can define this constraint explicitly. For example, you might add a constraint like:

ALTER TABLE profiles ADD CONSTRAINT profiles_id_fkey FOREIGN KEY (id) REFERENCES auth.users (id) ON DELETE CASCADE;

This command tells the database that the id column in the profiles table is a foreign key that references the id column in the auth.users table. The ON DELETE CASCADE part means that if a user record is deleted from auth.users , the corresponding record in profiles will also be automatically deleted. Again, use CASCADE wisely!

This setup ensures that your profiles table is always in sync with your authenticated users, providing a solid foundation for building rich user experiences. It’s all about making sure your data is organized, linked, and ready for retrieval when you need it.

Performing the JOIN Operation

Now for the really exciting part: stitching these two tables together using a JOIN operation! This is how you’ll fetch data from both auth.users and your profiles table in a single query. It’s like asking the database to show you a user’s email from the auth.users table and their full name and avatar from the profiles table, all at once.

The most common type of join you’ll use here is an INNER JOIN , but depending on your needs, a LEFT JOIN might also be super useful. Let’s break down how to do it.

Using INNER JOIN

An INNER JOIN returns only the rows where there is a match in both tables. So, if you have a user in auth.users but no corresponding entry in profiles (which shouldn’t happen if you’ve set up your foreign keys correctly and are creating profiles on user signup), that user won’t show up in the result. Likewise, if you somehow had a profiles entry without a matching user in auth.users (again, prevented by foreign keys), it wouldn’t show up either.

Here’s a basic example of an INNER JOIN to fetch a user’s email and their full name:

SELECT
  u.email,
  p.full_name,
  p.avatar_url
FROM
  auth.users AS u
INNER JOIN
  profiles AS p ON u.id = p.id;

Let’s dissect this query, guys:

• SELECT u.email, p.full_name, p.avatar_url : This specifies which columns you want to retrieve. We’re selecting the email from the auth.users table and full_name and avatar_url from the profiles table. Notice the use of aliases ( u for auth.users and p for profiles ). Aliases make your queries shorter and easier to read, especially when dealing with longer table names or multiple joins.
• FROM auth.users AS u : This indicates that we’re starting our query with the auth.users table and assigning it the alias u .
• INNER JOIN profiles AS p : This tells Supabase to join the auth.users table with the profiles table, which we’ve aliased as p .
• ON u.id = p.id : This is the crucial join condition . It tells the database how to match rows between the two tables. We’re matching rows where the id column in the auth.users table ( u.id ) is exactly equal to the id column in the profiles table ( p.id ). This is where our foreign key relationship comes into play.

This query will give you a list of all authenticated users who also have a profile entry, along with their email, full name, and avatar URL. It’s super handy for displaying user lists or fetching profile details for logged-in users.

Using LEFT JOIN

A LEFT JOIN is slightly different. It returns all rows from the left table ( auth.users in our case) and the matched rows from the right table ( profiles ). If there’s no match in the right table, the columns from the right table will contain NULL values.

This is incredibly useful if you want to list all users, including those who might not have completed their profile setup yet. You’d still get their email from auth.users , but full_name and avatar_url would be NULL for those users.

Here’s how a LEFT JOIN would look:

SELECT
  u.email,
  p.full_name,
  p.avatar_url
FROM
  auth.users AS u
LEFT JOIN
  profiles AS p ON u.id = p.id;

In this LEFT JOIN example, if a user exists in auth.users but doesn’t have a matching id in profiles , the full_name and avatar_url for that user will simply be NULL . This is perfect for scenarios where you need to display a complete list of users, even if some haven’t filled out all their profile details. You can then use conditional logic in your frontend to handle these NULL values gracefully, perhaps by showing a default avatar or a placeholder name.

Choosing between INNER JOIN and LEFT JOIN depends entirely on what data you need. If you only want users with complete profiles, use INNER JOIN . If you want all users and their associated profile info (or lack thereof), use LEFT JOIN . Both are powerful tools in your Supabase arsenal!

Fetching Data with Row Level Security (RLS)

Okay, guys, we can’t talk about Supabase without mentioning Row Level Security (RLS) . It’s a fundamental security feature that controls exactly who can access what data in your database. When you’re performing JOIN operations, especially involving sensitive user data, RLS is your best friend for keeping things secure.

By default, Supabase has some RLS policies set up for the auth.users table. For instance, an authenticated user can typically only see their own email address. They can’t just query SELECT * FROM auth.users and see everyone else’s emails, which is exactly what we want!

When you JOIN your profiles table with auth.users , you need to ensure your RLS policies allow the intended access. Let’s say you want authenticated users to be able to see their own profile information (email, full name, avatar) and perhaps the profile information of other users they might interact with (like seeing authors of posts).

Here’s how you might structure RLS policies for your profiles table, assuming you’ve set up the id foreign key relationship to auth.users :

1. Allow authenticated users to select their own profile: This policy ensures a user can view their own data in the profiles table. You’d typically write this policy in the Supabase SQL Editor under