Hello everyone,
given is a table with a version history kind of thing I am currently working on. Upon this table there is a view and the application interacts with the view only, updating/inserting/deleting is controlled by rules. It seems like the record set "OLD" gets changed when it is used in a SQL expression:
CREATE TABLE table1 ( id INTEGER NOT NULL, version INTEGER NOT NULL DEFAULT 0, vnoflag CHAR(1), content VARCHAR(20) );
INSERT INTO table1 (id, version, vnoflag, content) VALUES (1, 1, 'Y', 'Test');
CREATE VIEW view_table1 AS SELECT * FROM table1;
-- create a rule for update
CREATE OR REPLACE RULE ru_view_table1_update
AS
ON UPDATE TO view_table1 DO INSTEAD
(
-- insert a new record with the old id, old version number incremented
-- by one, versionflag set to 'Y' and the new content
INSERT INTO table1 (id, version, vnoflag, content) VALUES (OLD.id, OLD.version+1, 'Y', NEW.content);
-- update the old version and set its versionflag to 'N' as it is no
-- longer the current record
UPDATE table1 SET vnoflag = 'N' WHERE id = OLD.id AND version = OLD.version;
);
SELECT * FROM view_table1; id | version | vnoflag | content ----+---------+---------+--------- 1 | 1 | Y | Test (1 row)
UPDATE view_table1 SET content = 'New Test' WHERE id = 1 AND vnoflag = 'Y';
SELECT * FROM view_table1;
id | version | vnoflag | content
----+---------+---------+----------
1 | 1 | N | Test
1 | 2 | N | New Test
It seems like the UPDATE statement updates both the old and the new version. If I correctly go through the statements by hand, they should read:
INSERT INTO table1 (id, version, vnoflag, content) VALUES (1, 1+1, 'Y', 'New Test');
UPDATE table1 SET vnoflag = 'N' WHERE id = 1 AND version = 1;
If I change the UPDATE statement to read:
UPDATE table1 SET vnoflag = 'N' WHERE id = OLD.id AND vno = NEW.vno-1;
it works like expected:
id | version | vnoflag | content ----+---------+---------+---------- 1 | 2 | Y | New Test 1 | 1 | N | Test
Where is my logical error? Shouldn't the first UPDATE statement suffice?
Best regards ... Ralph ...
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