That's the new (in Postgres 14) syntax variant for SQL-standard functions.
The release notes:
Allow SQL-language functions and procedures to use SQL-standard function bodies (Peter Eisentraut)
Previously only string-literal function bodies were supported. When writing a function or procedure in SQL-standard syntax, the body is parsed immediately and stored as a parse tree. This allows better tracking of function dependencies, and can have security benefits.
Traditional Postgres functions and procedures save the body as literal string to be parsed at execution time, typically using dollar-quoting. See:
The new syntax
BEGIN ATOMIC ... END (with mandatory
ATOMIC!) does not quote the function body, which is parsed at creation time. It only looks similar to a PL/pgSQL block, which is decorated with
BEGIN ... END. Both are very much distinct. The new syntax variant is only allowed for
LANGUAGE sql. In fact, that language is assumed without declaration. The manual:
The default is
sql_body is specified.
You can write multiple pure-SQL statements, much like in traditional string-literal function or procedure bodies. But everything is parsed at function-creation time. So "early binding" vs. "late binding" for the traditional string-literal form. This has a number of side effects.
There is good explanation for SQL-standard syntax the in the manual:
This is similar to writing the text of the function body as a string
constant (see definition above), but there are some differences:
This form only works for
LANGUAGE SQL, the string constant form
works for all languages. This form is parsed at function definition
time, the string constant form is parsed at execution time; therefore
this form cannot support polymorphic argument types and other
constructs that are not resolvable at function definition time. This
form tracks dependencies between the function and objects used in the
function body, so
DROP ... CASCADE will work correctly, whereas the
form using string literals may leave dangling functions. Finally, this
form is more compatible with the SQL standard and other SQL implementations.
The new syntax variant will typically be preferable for simple SQL functions.
CREATE OR REPLACE FUNCTION asterisks(n int)
RETURNS SETOF text
LANGUAGE sql IMMUTABLE STRICT PARALLEL SAFE
SELECT repeat('*', g) FROM generate_series (1, n) g;