On Friday, April 17, 2015, Jim Nasby <
Jim.Nasby@bluetreble.com> wrote:
On 4/17/15 7:39 PM, David G. Johnston wrote:
On Friday, April 17, 2015, Jim Nasby <Jim.Nasby@bluetreble.com
<mailto:Jim.Nasby@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.