noob needs help with comparing feilds..

[fxr]

hi i am working on a web application and i am stuck..

 

i have a table that looks like this:

 

 

....time.........................quote....dif
| 2008-03-17 00:00:00 | 15000 | |
| 2008-03-17 00:30:00 | 15002 | |
| 2008-03-17 01:00:00 | 15004 | |
| 2008-03-17 01:30:00 | 15006 | |
| 2008-03-17 02:00:00 | 15008 | |
| 2008-03-17 02:30:00 | 15010 | |
| 2008-03-17 03:00:00 | 15008 | |
| 2008-03-17 03:30:00 | 15006 | |
| 2008-03-17 04:00:00 | 15004 | |
| 2008-03-17 04:30:00 | 15002 | |
| 2008-03-17 05:00:00 | 15000 | |
| 2008-03-17 05:30:00 | 15002 | |
| 2008-03-17 06:00:00 | 15004 | |
| 2008-03-17 06:30:00 | 15006 | |
| 2008-03-17 07:00:00 | 15008 | |
..etc etc

 

i wanna work out the difference in the quote from the previous 30 minutes and store it in the diff field

 

 

e.g

 

| 2008-03-17 00:00:00 | 15000 | null/0 |
| 2008-03-17 00:30:00 | 15002 | 2 |
| 2008-03-17 01:00:00 | 15004 | 2 |
..etc.etc

 

can i do this with a stored procedure or something? or should i use a script..? i just need a nudge in the right direction..

 

thanks.

[fenway]

Do you really need to store this?

[aschk]

Wow, makes my head spin. Hmm...

 

You need a self JOIN , on 1 row only. I'll give it some thought.

[fenway]

You could always use and order by clause and some user variables.