In the last episode (Aug 21), Ashish Mukherjee said:
> Well, since you are searching that column, it's probably a good idea.
>
> Possible scenarios for not storing computed values -
>
> 1) Data integrity - say, the columns A and B are updated but C does not get
> updated, resulting in an anomalo
Most alter table operations in 5.0 will rebuild the entire table. The
best thing to increase for alter table speed in innodb is the buffer
pool. For more details on how innodb handles alter table see
http://ebergen.net/wordpress/2007/05/07/how-alter-table-locks-tables-and-handles-transactions/
On
Something like this might work:
insert into domains
select a.accountid, reverse(a.domainid), a.mailname
from domains a
left outer join domains b on b.domainid = reverse(a.domainid) and
b.accountid = a.accountid and b.mailname = a.mailname
where b.domainid is null;
-Travis
If you want C to always be A-B then it would, in my opinion, be a very
bad idea to store C in the table. Instead you can just put C in your query.
SELECT `A`, `B`, `A` - `B` AS `C` FROM `table`
If that seems like a hassle, you could always create a view using that
select.
Chris W
b...@qxhp
Couple of thoughts ...
lsof -p may give some clue of what files/tables it's
reading/writing. From that you may be able to deduce something useful.
Check the slow query log and see if any of the queries are CPU-intensive (by
doing an EXPLAIN) and are the bottleneck.
- Ashish
On Fri, Aug 20, 201
Well, since you are searching that column, it's probably a good idea.
Possible scenarios for not storing computed values -
1) Data integrity - say, the columns A and B are updated but C does not get
updated, resulting in an anomalous situation
2) Data-set is large and the extra column leads to
Ashish, Mark and off-list responders,
Thanks!
Ashish, is there a really good general reason not to store a computed
value? Searches will be done on this column. Searches like 'Please send me
the rows with the ten highest values of C.'
> Do you have a really good reason to store a computed value?
Do you have a really good reason to store a computed value? It's only useful
if you will perform a search on the column, else you could just do the
subtraction when you SELECT columns A and B.
- Ashish
On Sat, Aug 21, 2010 at 11:55 AM, wrote:
> Hello,
>
> For simplicity's sake, let's say I have
On 21/08/2010 07:25, b...@qxhp.com wrote:
Hello,
For simplicity's sake, let's say I have three fields, A, B and C, all
of which are integers. I'd like the value of C to be equal to A less B
(A-B). Is there a way I can perform this calculation? I'm guessing it
would happen when I INSERT a row and
