DiffKit is Free and Open Source Software (FOSS).
http://www.diffkit.org
DiffKit is an application, and a framework, for comparing two tables
of data, field-by-field. The tables can come from any of a number of
sources, such as an RDBMS or CSV file, and DiffKit is able to mix
different kinds of sources in the same diff operation. DiffKit is like
the Unix diff utility, but for tables instead of lines of text.
DiffKit is now tested against PostgreSQL 9.0. It allows Postgres
users to produce structured reports that precisely describe the
differences between two tables, in the same way that *nix "diff"
produces a structured report to describe the differences between two
text files. It supports: both tables in same DB, tables in different
Postgres DBs, one table in Postgres DB, the other in Oracle, DB2,
MySQL, SQLServer, H2.
DiffKit is a very high quality project that maintains all supported
databases under a suite of regression tests. These regression tests
are embedded within the normal application distribution, so that end
users can run the tests themselves, and also examine the scope and
content of the tests. Each test is fully documented.
DiffKit also has a Java programming API that features a clean OOP
design. As a result, it's quite easy to customize DiffKit to produce
specialized comparisons or reports.