Using the "exit" statement to jump out of a block statement

The exit statement is legal, and has well-defined semantics, within a simple block statement, even when it isn't inside a loop statement. This means that you can use it anywhere in the PL/pgSQL text that defines the implementation of a do statement or a language plpgsql subprogram. If you label the top-level block statement that defines the implementation with, for example, top level block, then use can use this:

exit top_level_block when <boolean expresssion>:

as a more compact alternative to the bare return statement within an if statement:

if <boolean expresssion> then
  return;
end if;

(The bare return statement is legal, and has well-defined semantics, in a do statement's implementation and in a language plpgsql procedure. The other forms of the return statement are legal only in a language plpgsql function.)

Try this:

\c :db :u
drop schema if exists s cascade;
create schema s;

create function s.f(n in int)
  returns text
  language plpgsql
as $body$
declare
  v text not null := 'a';
begin
  <<b1>>begin
    exit b1 when length(v) >= n;
    v := v||'b';
    exit b1 when length(v) >= n;
    v := v||'c';
    exit b1 when length(v) >= n;
    v := v||'-impossible';
  end b1;
  return v;
end;
$body$;

This finishes without error. Now test it. First like this:

select s.f(1);

This is the result:

 a

Next like this:

select s.f(2);

This is the result:

 ab

And finally like this:

select s.f(3);

This is the result:

 abc

Now try this counter example:

create procedure s.bad()
  language plpgsql
as $body$
begin
  exit;
end;
$body$;

It causes the 42601 syntax error:

EXIT cannot be used outside a loop, unless it has a label

Finally try this counter example:

create procedure s.bad()
  language plpgsql
as $body$
<<b1>>begin
  loop
    continue b1;
  end loop;
end b1;
$body$;

It, too, causes the 42601 syntax error, but now with this wording:

block label "b1" cannot be used in CONTINUE

This is the meaning:

• Neither the continue statement (without a label) nor the continue <label> statement can be used outside a loop.
• When the continue <label> statement is used, as it must be, within a loop, the label must match that of an enclosing loop statement.

There's an example of the legal use of the continue <label> statement, where the label matches that of an enclosing loop statement, in the function s.vowels_from_lines() on the page «Two case studies: Using the "for" loop, the "foreach" loop, the "infinite" loop, the "exit" statement, and the "continue" statement» in Case study #2.

Look for this:

continue lines when c = prev;