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Writing User-Defined Functions in PostgreSQL

Introduction
Side-effects in functions
Invoking functions

Instruction

Cool! As we just learned, there are a few ways of calling a function:

  • Using a SELECT statement. You can use a regular SELECT in SQL (not in PL/pgSQL):
    SELECT add_topic('Quick cakes');
  • In PL/pgSQL, you can:
    • Use the SELECT INTO syntax to save a query result: 
      SELECT thumbs_up, thumbs_down
INTO upvotes, downvotes
FROM post
WHERE id = post_id
    • Use assignment to save the query result: 
      post_id := (
  SELECT post_id
  FROM post
  WHERE user_id = 17
  LIMIT 1
);
    • Use assignment to invoke a function: 
      user_id := get_most_active_user();
    • PERFORM statement (in PL/pgSQL). 
      PERFORM add_topic('Quick cakes');

Exercise

Click Next exercise to jump to the next part where we're going to continue our adventure with complex functions!