You just need :
- to define the way to find the previous row
- an BEFORE INSERT trigger to compute the checksum, read up some pg/plsql or SQL to write your function. To read the row as a whole just use the table name without column in the select
- two rules (update / delete) to do nothing
On 13/11/2017 08:15, Iaam Onkara wrote:
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,
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
--
Achilleas Mantzios
IT DEV Lead
IT DEPT
Dynacom Tankers Mgmt