Thread: Joins involving functions

I have a function that returns a row from a table, e.g.:

create table foo (a integer);

create function f_foo (integer) returns foo language 'sql'
as $foo$ select * from foo where a = $1 limit 1
$foo$

create table bar (b integer);

select * from bar
cross join f_foo(bar.b) as foo;

Unfortunately, this last statement returns an error:

NOTICE:  adding missing FROM-clause entry for table "bar"
ERROR:  function expression in FROM may not refer to other relations of
same query level

Is there a method for joining function calls to tables? The only other
approach I can think of is to write another function that returns "setof".

-- 
Jeffery Boes  <><
jeff@endpoint.com

Hi, Jeff Boes,

Jeff Boes wrote:

> select * from bar
> cross join f_foo(bar.b) as foo;
> 
> Unfortunately, this last statement returns an error:
> 
> NOTICE:  adding missing FROM-clause entry for table "bar"
> ERROR:  function expression in FROM may not refer to other relations of
> same query level
> 
> Is there a method for joining function calls to tables? The only other
> approach I can think of is to write another function that returns "setof".

I don't exactly know what you want to achieve, so I'm just wildly guessing.

Do you really want the cross join between bar.* and f_foo(bar.b)?

If yes, use

SELECT x.b, y.b FROM bar x CROSS JOIN bar y;

If not, you maybe want

SELECT b, f_foo(b) FROM bar;

Or it may be you want something like:

SELECT * from bar CROSS JOIN (SELECT f_foo(bar.b) from bar) as foo ;


HTH,
Markus
-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

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