Take this query I'm running from the mysql commandline:

SELECT name,
SUM(joined_0) AS J0,
SUM(joined_1) AS J1,
ABS(SUM(joined_0) - SUM(joined_1)) AS J_Diff,
SUM(joined_0)/(SUM(joined_0) + SUM(joined_1))*100 AS J0_Pcnt,
SUM(joined_1)/(SUM(joined_0) + SUM(joined_1))*100 AS J1_Pcnt
FROM ps_people p,
ps_pdata d,
ps_pdata_etc e
WHERE d.dataid = e.dataid AND
d.pid = p.pid
GROUP BY d.plrid
HAVING J0 > 0 AND
J1 > 0
ORDER BY J_Diff ASC
LIMIT 20;




1) Why is it I can't use J0 and J1 in the definition for J_Diff and
J0_Pcnt, J1_Pcnt

2) Is there any way to do it that I'm missing here?

I guess mainly I want ot save typing and it seems really redundant and
error prone to write a query the way I wrote it, and aliasing seemed
like it would make things less cluttered but all I get is 'Unknown
Column'

Thanks for any help.