On Friday, April 17, 2015, Jim Nasby <jim.na...@bluetreble.com> wrote:
> On 4/17/15 7:39 PM, David G. Johnston wrote: > >> On Friday, April 17, 2015, Jim Nasby <jim.na...@bluetreble.com >> <mailto:jim.na...@bluetreble.com>> wrote: >> >> I'm working on a function that will return a set of test data, for >> unit testing database stuff. It does a few things, but ultimately >> returns SETOF record that's essentially: >> >> RETURN QUERY EXECUTE 'SELECT * FROM ' || table_name; >> >> Because it's always going to return a real relation, I'd like to be >> able to the equivalent of: >> >> SELECT ... FROM my_function( 'some_table' )::some_table; >> >> >> Unfortunately this means "cast the existing type to some_table" and >> "record" is not a valid type in this context. >> >> >> Is there any trick that would allow that to work? I know that >> instead of 'SELECT * ...' I can do 'SELECT row(t.*) FROM ' || >> table_name || ' AS t' and then do >> >> SELECT ... FROM my_function( 'some_table' ) AS data( d some_table ) >> >> but I'm hoping to avoid the extra level of indirection. >> >> Haven't explored this specific code in depth...but which part - the >> function alias or the select row(t.*)? They seem to be independent >> concerns. >> > > I'm saying that I know I can use the row construct as a poor work-around. > What I actually want though is a way to tell this query: > > SELECT ... FROM my_function( 'some_table' ) > > that my_function is returning a record that exactly matches "my_table". I > suspect there's not actually any way to do that :( > > No matter what you do inside the function you have to write that last query as "from my_function('some_table') AS (rel some_table)" otherwise the planer is clueless. You cannot defer the type until runtime. Your cast form is slightly more succinct but I cannot see making it work when the current method is serviceable. Inside the function I would have thought that select * shoud work - no need to use the row(t.*) construct - but the later seems reasonably direct... If you could find a way to pass a value of type some_table into the function - instead of the name/text 'some_table‘ - you could possibly use polymorphic pseudotypes...just imagining here... Select ... From my_func(null::some_table) Create function my_func(tbl any) returns setof any .... Use typeof to get a text string of the tbl arg's type. You could maybe also return a refcursor... David J.
