You could use the OpenESQL technology if you had an appropriate ODBC driver for Ingres on RHEL

A google search showed one such possibility which works with unixODBC manager.

community.actian.com/.../Ingres_UNIX_ODBC

Ingres also appears to have its own precompiler for COBOL called esqlcbl, although I do not know anything about it.

Also found a reference to the docs in the following link. although it appears to be quite old.

downloads.actian.com/.../esql.pdf

Thanks