til/postgres/use-variables-in-an-anonymous-function.md

Use Variables In An Anonymous Function

I was curious how variables could be declared and used in PostgreSQL, so I did a little experiment with a books and authors schema.

Variables need to be declared and used within the context of a function. Using the do syntax I am able to declare and execute an anoymous code block.

Within that code block I can declare one or more variables by giving them a type and optionally a default value. Below I declare author_id with a default and result as a record type.

do $$
declare
  author_id varchar := 'e2b42ebf-7ea9-4d9e-8edf-310fc1894bcd';
  result record;
begin
  for result in select title from books where "authorId" = author_id
  loop
    raise notice '| % |', result.title;
  end loop;
end $$;

I'm able to use the author_id variable directly in a select statement.

select title from books where "authorId" = author_id

and then using a for loop with my result of record type, I can iterate over each of the results from the select.

Because this anonymous do block implicitly has a void return type, I need to do something with the result within the block. For demonstration purposes, I use raise notice to log out each book title.