Hi,
you can easily join the preceeding row, e.g.
select sub.id, sub.created_at, preceedingid, m2.* from (
select m.id, m.created_at, lag(m.id) over(order by m.created_at) as preceedingid from test m
order by m.created_at) as sub
left join test m2 on m2.id=sub.preceedingid order by sub.created_at;
Regards, Martin
Am 13.11.2017 um 07:15 schrieb Iaam Onkara:
Hi,
I have a requirement to create an tamper proof chain of records for audit purposes. The pseudo code is as follows
before_insert:
1. compute checksum of previous row (or conditionally selected row)
2. insert the computed checksum in the current row
3. using on-update or on-delete trigger raise error to prevent update/delete of any row.
Here are the different options that I have tried using
lag and
md5 functions
http://www.sqlfiddle.com/#!17/69843/2CREATE TABLE test
("id" uuid DEFAULT uuid_generate_v4() NOT NULL,
"value" decimal(5,2) NOT NULL,
"delta" decimal(5,2),
"created_at" timestamp default current_timestamp,
"words" text,
CONSTRAINT pid PRIMARY KEY (id)
)
;
INSERT INTO test
(value, words)
VALUES
(51.0, 'A'),
(52.0, 'B'),
(54.0, 'C'),
(57.0, 'D')
;
select
created_at, value,
value - lag(value, 1, 0.0) over(order by created_at) as delta,
md5(lag(words,1,words) over(order by created_at)) as the_word,
md5(textin(record_out(test))) as Hash
FROM test
ORDER BY created_at;
But how do I use lag function or something like lag to read the previous record as whole.
Thanks,
Onkara
PS: This was earlier posted in 'pgsql-in-general' mailing list, but I think this is a more appropriate list, if I am wrong I am sorry
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