Re: md5 checksum of a previous row

select m2.* from .... will do the job in my example

Am 13.11.2017 um 08:39 schrieb Iaam Onkara:
> Thanks that is very helpful.
>
> Now is there a way to fetch previous record without having to specify
> the different column names? Seems to me this should be a  first class
> function in PostgreSQL, but its not.
>
> On Mon, Nov 13, 2017 at 1:31 AM, MS (direkt)
> <martin(dot)stoecker(at)stb-datenservice(dot)de
> <mailto:martin(dot)stoecker(at)stb-datenservice(dot)de>> wrote:
>
> Hi,
>
> you can easily join the preceeding row, e.g.
>
> select sub.id <http://sub.id>, sub.created_at, preceedingid, m2.*
> from (
> select m.id <http://m.id>, m.created_at, lag(m.id <http://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 <http://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/#!17/69843/2
>> <http://www.sqlfiddle.com/#%2117/69843/2>
>>
>> CREATE 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
>
> --
> Widdersdorfer Str. 415, 50933 Köln
> <https://maps.google.com/?q=Widdersdorfer+Str.+415,+50933+K%C3%B6ln&entry=gmail&source=g>; Tel.+49 / 221 / 9544 010 <tel:+49%20221%209544010>
> HRB Köln HRB 75439, Geschäftsführer: S. Böhland, S. Rosenbauer
>
>

--
Widdersdorfer Str. 415, 50933 Köln; Tel. +49 / 221 / 9544 010
HRB Köln HRB 75439, Geschäftsführer: S. Böhland, S. Rosenbauer