Using SQL to join an i5/os databasde and a Windows database

I am supporting a Windows application that is built on MS-SQL database. I write
Crystal reports, among other things.

I need to retrieve data from the i5 (forgive me, I still do not know what the
current name is) based on data from the MS-SQL database.

Bad news is that the key field I am using on the MS-SQL database is a character
field, which I convert to a numeric fiel to access the i5. The only direct way
to do that with standard Crystal syntax is to use a subreport. VERY VERY, VERY
SSSSSLLLLLLOOOOOOOOOOWWWWWWWWWWW.

In addition, the key field I am using is incomplete, as the database I am
accesing has two key fields: the one I have as second key, and a numeric field
(fixed value of 1 in this case) as the first key.

Since Crystal does allow SQL to be used, I was wondering if that would allow for
faster processing. Specifically, can a join be constructed between the two
systems so that the sub report is not needed?

Specifically, on the MS-SQL database, I have a string field, length 20. The
numeric field on the (I wish I knew the proper name. Keep wanting to say
AS/400, and I know from reading previous posts that is a dead name) i5 is
numeric, 7 packed, no decimal places. I think I might have tried, but can't
remember, creating a numeric field on the MS-SQL database and tring to link
that. If I recall, that fails because the field I create is not a database
field. Could be mistaken. Been a long time ago.

Sorry for the long winded question. But, I have to do something to improve
performance. I ran this mess for six hours today, and created a partial report
about 180 pages. Full report would be around 1000. This can't be good for
either MS-SQL or the i5 to do this much heavy lifting.

Thanks for suggestions.

John McKee