The PL/pgSQL "return" statement
plpgsql_return_stmt ::= RETURN [ expression | NEXT | NEW | OLD | NULL ]
The bare "return" statement
You can use the bare return statement to exit from any top-level PL/pgSQL block statement (even if it is invoked within a deeply-nested block statement). In particular, you can use it to exit from a procedure or a do statement. However, this use is very rarely seen—and many programers would consider it to be a bad practice. Rather, the preferred practice is to let the point of execution simply reach the final end;— by virtue of the use of "proper" flow control with the if statement or the case statement. Then the procedure is automatically exited just as if the bare return were written here (and only here).
The "return expression" statement
This is legal only in a regular function (but not in a table function). In fact every regular function must have at least one such statement and the point of execution must reach one of these. If you fail to satisfy this rule, then there's no syntax error. But you'll get the 2F005 run-time error saying that the function finished without executing a return expression statement. The expression must match what the returns clause, in the function's header, specifies.
The "return next" statement
This is legal only in a table function. In fact every table function must have at least one such statement and the point of execution must reach one of these. Often, the return next statement is written within a loop so that the table function returns many rows. Notice that the return next statement takes no argument. Rather, you must assign value(s) ordinarily before invoking it, just as if these identified ordinary in out formal arguments, using the identifier(s) that the returns table(...) clause, in the function's header, specifies.
The "return new", "return old" and "return null" statements
These are legal only in a DML trigger function. In fact every DML trigger function must have at least one such statement and the point of execution must reach one of these. A DML trigger function is created as such by using the returns trigger clause in the function's header.
Coming soonMore detail, and code examples, about these uses will follow.