LATERAL and VOLATILE functions

Hello

I tested some usage of LATERAL clause, and I found so LATERAL doesn't
respects difference between VOLATILE and IMMUTABLE functions.

Is this behave expected?

-- unexpected
postgres=# select * from generate_series(1,3) g(v), LATERAL (SELECT random()) x;
;
v │ random
───┼──────────────────
1 │ 0.63025646051392
2 │ 0.63025646051392
3 │ 0.63025646051392
(3 rows)

-- expected
postgres=# select * from generate_series(1,3) g(v), LATERAL (SELECT
random() - v + v) x;
v │ ?column?
───┼───────────────────
1 │ 0.381548477802426
2 │ 0.762988060247153
3 │ 0.181648664642125
(3 rows)

Regards

Pavel Stehule