Introduction
Side-effects in functions
Invoking functions
Instruction
Great! The regular SELECT query does not work in a function body. Let's see an example:
CREATE FUNCTION get_most_active_user()
RETURNS void AS $$
BEGIN
SELECT u.*
FROM user_account AS u
JOIN post AS p
ON u.id = p.user_id
GROUP BY 1
ORDER BY COUNT(1) DESC
LIMIT 1;
END;
$$ LANGUAGE plpgsql;
SELECT get_most_active_user();
The body of this function simply runs a SELECT query. However, when you try to invoke the function you'll, get an error.
Exercise
Run the template query. Observe that PostgreSQL does not allow you to invoke a SELECT query without storing its value in a variable.
