How Do I Query Latest Dates across Columns?

[WarcraftNoob]

This is what I have right now,

SELECT  Project, S_on, P_on, H_on, A_on, I_on, 1_on, 2_on, 3_on, 4_on, Z_on, D_on, T_on, K_on, F_on, J_on, FINAL_on
From DTable
WHERE
Class='XXX' AND 
Project like 'Proj%' AND QA= 'ST'  AND FINAL_on is not NULL
 

This will query make me a nice big table,

Proj1.xxx  DATE DATE DATE DATE DATE NULL DATE.... FINAL_onDATE
Proj1.xxx  DATE DATE DATE DATE DATE DATE DATE.... FINAL_onDATE
Proj1.xxx  DATE NULL DATE DATE NULL DATE DATE.... FINAL_onDATE
Proj2.xxx  DATE DATE DATE DATE DATE DATE DATE.... FINAL_onDATE
Proj2.xxx  DATE DATE DATE DATE DATE DATE DATE.... FINAL_onDATE
Proj3.xxx  DATE DATE DATE NULL DATE DATE DATE.... FINAL_onDATE
 

where date are in the form DD-MMM-YY (eg 24-JUN-08)

but what I want is the max (latest) date out of

S_on, P_on, H_on, A_on, I_on, 1_on, 2_on, 3_on, 4_on, Z_on, D_on, T_on, K_on, F_on, J_on


And then

FINAL_on - maxdate(above) which would return number of days

Then the avg of the days ( sum of days / count(projects) ) for each project


So I would want something like to be queried

PROJ  XXX   FINAL_on-maxdate   FINAL_on - maxdate / XXX
A     3      100               33.33
B     4      200               50
C     3      33                11
D     7      2                 ...
E     8      365               ....
 

I just need the first and last columns to be displayed. Thanks :)

[Atli]

I don't really understand what the data in this table is used for.

What are all the X_on fields?

If each of the X_on fields are meant to represent a milestone, leading to a final "turn in" date, would it not be best to store these in a separate table?
Like:

Project
-----------
ProjectID Serial Primary Key
ProjectName VarChar
etc..
----------
 
MileStone
----------
MSID Serial Primary Key
MSName VarChar
MSDate DateTime
ProjectID BigInt References Project(ProjectID)
----------
 

Then you could query that table, rather than having to manually check the various fields in the main table.