There's a blog for SQL Server that says returning a scalar using
SELECT is wasteful:
SELECT should be used for returning resultsets, not scalars. This procedure uses a SELECT statement to return a single value to the client. This is inefficient because most applications will have to prepare additional objects (typically referred to as "recordsets") and other support in order to consume the result. While it is certainly valid syntax to use SELECT to return scalar values, this does not need to be common in production code. This is the kind of thing that can make it slightly harder for high-end applications to scale.
Does this apply to PostgreSQL as well? Should functions always use
RETURN for outputting scalars, or is it ok to use
SELECT whenever it's more convenient?