depth-first search order. Upon close reading of SQL:2008, it seems that the
spec's SEARCH DEPTH FIRST and SEARCH BREADTH FIRST options do not actually
guarantee any particular result order: what they do is provide a constructed
column that the user can then sort on in the outer query. So this is actually
just as much functionality ...
pseudo-type record[] to represent arrays of possibly-anonymous composite
types. Since composite datums carry their own type identification, no
extra knowledge is needed at the array level.
The main reason for doing this right now is that it is necessary to support
the general case of detection of cycles in recursive queries: if you need to
compare more than one column to detect a cycle, you need to compare a ROW()
to an array built from ROW()s, at least if you want to do it as the spec
suggests. Add some documentation and regression tests concerning the cycle
detection issue.
RecursiveUnion to which it refers. It turns out that we can just postpone the
relevant initialization steps until the first exec call for the node, by which
time the ancestor node must surely be initialized. Per report from Greg Stark.
implementation uses an in-memory hash table, so it will poop out for very
large recursive results ... but the performance characteristics of a
sort-based implementation would be pretty unpleasant too.
recursive CTE that we're still in progress of analyzing. Add a similar guard
to the similar code in expandRecordVariable(), and tweak regression tests to
cover this case. Per report from Dickson S. Guedes.
There are some unimplemented aspects: recursive queries must use UNION ALL
(should allow UNION too), and we don't have SEARCH or CYCLE clauses.
These might or might not get done for 8.4, but even without them it's a
pretty useful feature.
There are also a couple of small loose ends and definitional quibbles,
which I'll send a memo about to pgsql-hackers shortly. But let's land
the patch now so we can get on with other development.
Yoshiyuki Asaba, with lots of help from Tatsuo Ishii and Tom Lane
