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Thread: Extract created and last modified data

Extract created and last modified data

From
Gordon McVey
Date:
I have a CMS with a table of items, and another table serving as a log <br /> of operations performed on the items.
 Therevelent table structure is <br /> as follows: <br /><p>items <br /> itm_id | usr_id_create | itm_date_create |
usr_id_modify| <br /> itm_date_modify | ..... <br /><p>itm_id is a serial primary key. <br /><p>usr_id_* are the keys
ofthe users who created and last modified the <br /> item. <br /><p>item_date_* are timestamps for creation and last
modificationtimes. <br /><p>changelog <br /> itm_id | usr_id | log_timestamp | log_op <br /><p>itm_id and usr_id are
foreignkeys into the respective item and user <br /> tables.  log_timestamp is when the last change was made and log_op
was<br /> the operation performed. <br /><p>I realised that the creation and last modified data was being stored <br />
intwo places, and this is causing some issues with desynching.  I'm <br /> thinking of removing the creation and last
modifiedfields from the <br /> items table and using a view to fetch the create data and ID, and the <br /> last
modifieddate and ID from the changelog table instead.  However <br /> I'm not sure of how to do this, and how it would
impactperformance. <br /><p>Can anybody help with writing the query to get a view that replicates <br /> the items
tableexcept with the create and last modified user IDs and <br /> timestamps loaded from the changelog table?  If there
isanybody who <br /> has actually implemented something similar, what kind of performance <br /> impact would it have?
<br/>

Re: Extract created and last modified data

From
"Oliveiros d'Azevedo Cristina"
Date:
Howdy, Gordon.
 
This query is an attempt to replicate your items table with data just from changelog table.
Could you please try it out?
 
Best,
Oliveiros
 
SELECT itm_id,usr_id_create, itm_date_create, usr_id_modify, itm_date_modify
FROM
(
SELECT a.itm_id, a.usr_id as usr_id_create, create as itm_date_create
FROM  changelog  a
JOIN
(SELECT MIN(log_timestamp) as create, itm_id FROM changelog GROUP BY itm_id) b
ON (a.itm_id = b.itm_id
AND log_timestamp = create)
) subquery1
NATURAL JOIN
(
SELECT c.itm_id, usr_id as usr_id_modify, last_modified as itm_date_modify
FROM changelog c
JOIN (SELECT MAX(log_timestamp) as last_modified, itm_id FROM changelog GROUP BY itm_id) d
ON (d.itm_id = c.itm_id
AND c.log_timestamp = last_modified)
) subquery2
 
 
 

I have a CMS with a table of items, and another table serving as a log
of operations performed on the items.  The revelent table structure is
as follows:

items
itm_id | usr_id_create | itm_date_create | usr_id_modify |
itm_date_modify | .....

itm_id is a serial primary key.

usr_id_* are the keys of the users who created and last modified the
item.

item_date_* are timestamps for creation and last modification times.

changelog
itm_id | usr_id | log_timestamp | log_op

itm_id and usr_id are foreign keys into the respective item and user
tables.  log_timestamp is when the last change was made and log_op was
the operation performed.

.

Can anybody help with writing the query to get a view that replicates
the items table except with the create and last modified user IDs and
timestamps loaded from the changelog table?  If there is anybody who
has actually implemented something similar, what kind of performance
impact would it have?