Returning Multiple Values from an Extension Function
The second extension that you will add works well with the filesize function. Given the name of a directory, the filelist function returns a list of all files (and subdirectories) contained in that directory. The filesize function (from the previous example) returns a single value; filelist will return multiple rows. An extension function that can return multiple results is called a set-returning function, or SRF.
PostgreSQL's SRF Interface
Before you read too much further, I should tell you that there's an easy way to write set-returning functions and another method that's almost as easy. I'll describe both methods, starting with the slightly more difficult approach. Starting with version ...