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 specify the values for A and B.
Feel free
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
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, b...@qxhp.com wrote:
Hello,
For simplicity's sake, let's
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?
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
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
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 anomalous
