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Database Functions

Postgres has built-in support for SQL functions. These functions live inside your database, and they can be used with the API.

Quick demo#

Getting started#

Supra provides several options for creating database functions. You can use the Dashboard or create them directly using SQL. We provide a SQL editor within the Dashboard, or you can connect to your database and run the SQL queries yourself.

  1. Go to the "SQL editor" section.
  2. Click "New Query".
  3. Enter the SQL to create or replace your Database function.
  4. Click "Run" or cmd+enter (ctrl+enter).

Simple Functions#

Let's create a basic Database Function which returns a string "hello world".


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create or replace function hello_world() -- 1
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returns text -- 2
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language sql -- 3
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as $$ -- 4
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select 'hello world'; -- 5
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$$; --6

Show/Hide Details

At it's most basic a function has the following parts:

  1. create or replace function hello_world(): The function declaration, where hello_world is the name of the function. You can use either create when creating a new function or replace when replacing an existing function. Or you can use create or replace together to handle either.
  2. returns text: The type of data that the function returns. If it returns nothing, you can returns void.
  3. language sql: The language used inside the function body. This can also be a procedural language: plpgsql, plv8, plpython, etc.
  4. as $$: The function wrapper. Anything enclosed inside the $$ symbols will be part of the function body.
  5. select 'hello world';: A simple function body. The final select statement inside a function body will be returned if there are no statements following it.
  6. $$;: The closing symbols of the function wrapper.

After the Function is created, we have several ways of "executing" the function - either directly inside the database using SQL, or with one of the client libraries.


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select hello_world();

Returning data sets#

Database Functions can also return data sets from Tables or Views.

For example, if we had a database with some Star Wars data inside:

Planets

idname
1Tattoine
2Alderaan
3Kashyyyk

People

idnameplanet_id
1Anakin Skywalker1
2Luke Skywalker1
3Princess Leia2
4Chewbacca3

We could create a function which returns all the planets:


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create or replace function get_planets()
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returns setof planets
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language sql
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as $$
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select * from planets;
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$$;

Because this function returns a table set, we can also apply filters and selectors. For example, if we only wanted the first planet:


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select *
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from get_planets()
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where id = 1;

Passing parameters#

Let's create a Function to insert a new planet into the planets table and return the new ID. Note that this time we're using the plpgsql language.


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create or replace function add_planet(name text)
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returns bigint
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language plpgsql
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as $$
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declare
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new_row bigint;
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begin
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insert into planets(name)
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values (add_planet.name)
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returning id into new_row;
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return new_row;
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end;
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$$;

Once again, you can execute this function either inside your database using a select query, or with the client libraries:


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select * from add_planet('Jakku');

Suggestions#

Database Functions vs Edge Functions#

For data-intensive operations, use Database Functions, which are executed within your database and can be called remotely using the REST and GraphQL API.

For use-cases which require low-latency, use Edge Functions, which are globally-distributed and can be written in Typescript.

Security definer vs invoker#

Postgres allows you to specify whether you want the function to be executed as the user calling the function (invoker), or as the creator of the function (definer). For example:


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create function hello_world()
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returns text
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language plpgsql
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security definer set search_path = public
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as $$
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begin
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select 'hello world';
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end;
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$$;

It is best practice to use security invoker (which is also the default). If you ever use security definer, you must set the search_path. This limits the potential damage if you allow access to schemas which the user executing the function should not have.

Function privileges#

By default, database functions can be executed by any role. You can restrict this by altering the default privileges and then choosing which roles can execute functions.


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ALTER DEFAULT PRIVILEGES REVOKE EXECUTE ON FUNCTIONS FROM PUBLIC;
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-- Choose which roles can execute functions
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GRANT EXECUTE ON FUNCTION hello_world TO authenticated;
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GRANT EXECUTE ON FUNCTION hello_world TO service_role;

Resources#

Deep Dive#

Create Database Functions#

Call Database Functions using JavaScript#

Using Database Functions to call an external API#

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