Disclaimer: IANAL, nor do I play one in major broadway shows. You should
most definately consult a lawyer with IP experience before shipping
software based on any 3rd party software, be it open source or not.

With that out of the way, my understanding of the license is as follows:

You are not disallowed to charge for Ingres, but if you distribute
binaries to anyone (making it available for download counts as
distributing) you have to make the source that was used to build
those binaries available to people you distributed those binaries to
when they request it, and these sources (including any changes you made
to Ingres) would have to be made available to those people under the
CA-TOSL or a license that is compatible with it (and for license
compatibility you *must* consult a proper lawyer). Note that this *will*
allow those people to redistribute your changed sources. If you never
distribute the changed Ingres outside of your organisation, you could
keep your changes private.

But given the fact that your clients would be allowed to redistribute
the changed sources anyway, why would you *not* want to make your
changes available to CA for inclusion in the mainstream Ingres? If you
do it'd mean less work for you, if you don't it means that with every
new release of Ingres you'd have to re-port your own patches and do all
the testing on your own. Don't underestimate the work involved in that!
And that's assuming you know how to test a new Ingres build properly,
which, no offence, you probably don't. CA does.