recursive sql mathematics in sql?

Question

I want to retrieve the last three children of my parent. Currently the statement reads:

SELECT * 
from replies 
order by rID,rValue

Because rValue signifies the reply mechanism a null rValue means that is the parent. To allow replies to replies rValue goes x to x.999999 and I was hoping there is some way to retrieve the last three results for each parent. Please hit me up if any further clarification is required.

EDIT: Lets say a limit of 30 thread per page and a maximum of 1000replies per thread would it be a huge strain on the DB just to get all the results then cycle through to the last 3 of each?

MySQL recursion

Tim Lehner
– Tim Lehner

2012-04-02 14:15:40 +00:00
Commented Apr 2, 2012 at 14:15 — Tim Lehner
– Tim Lehner, Commented Apr 2, 2012 at 14:15

Pablo Santa Cruz · Accepted Answer · 2012-04-02 12:23:25Z

0

You need common table expression and recursive queries. Take a look at your RDBMS if it supports them.

answered Apr 2, 2012 at 12:23

Pablo Santa Cruz

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