tempx and tempx2 are tables with single int4 field. Having single record
with value of 1 in both tables:
vac=> explain select * from tempx, tempx2 where tx = tx2;
NOTICE: QUERY PLAN:
Hash Join (cost=17.20 size=100 width=8)
-> Seq Scan on tempx2 (cost=4.30 size=100 width=4)
-> Hash (cost=0.00 size=0 width=0)
-> Seq Scan on tempx (cost=4.30 size=100 width=4)
EXPLAIN
vac=> begin;
BEGIN
vac=> declare c cursor for select * from tempx, tempx2 where tx = tx2;
SELECT
vac=> fetch 1 in c;
tx|tx2
--+---
0| 0
(1 row)
vac=> fetch 1 in c;
tx|tx2
--+---
1| 1
(1 row)
vac=> fetch backward 1 in c;
tx|tx2
--+---
0| 0
(1 row)
^^^^^^^^^^^^^^^^^^^^^^ - very nice!
vac=> end;
END
vac=> insert into tempx values (1);
INSERT 320416 1
vac=> begin;
BEGIN
vac=> declare c cursor for select * from tempx, tempx2 where tx = tx2;
SELECT
vac=> fetch 1 in c;
tx|tx2
--+---
0| 0
(1 row)
vac=> fetch 1 in c;
tx|tx2
--+---
1| 1
(1 row)
vac=> fetch backward 1 in c;
tx|tx2
--+---
1| 1
(1 row)
^^^^^^^^^^^^^^^^^^^^^^^^^^
HashJoin doesn't care about scan dirrection...
This is another story:
vac=> fetch backward 1 in c;
tx|tx2
--+---
0| 0
(1 row)
vac=> fetch backward 1 in c;
tx|tx2
--+---
(0 rows)
vac=> fetch 1 in c;
PQexec() -- Request was sent to backend, but backend closed the channel before responding.
This probably means the backend terminated abnormally before or while processing the request.
Vadim
