Jailer is an Open Source app for database subsetting, schema, and data browsing.

It allows you to export consistent, referentially intact row-sets from relational databases and removes obsolete data without violating integrity. It is DBMS agnostic (by using JDBC), platform independent, and generates DbUnit datasets, hierarchically structured XML, and topologically sorted SQL-DML.

Other features include exporting consistent and referentially intact row-sets from your productive database and imports the data into your development and test environment. Improves database performance by removing and archiving obsolete data without violating integrity. Generates hierarchically structured XML, topologically sorted SQL-DML and DbUnit datasets.
Open Source. Entirely written in Java. Platform independent. DBMS agnostic.

There aren't too many apps out there we are aware of like Jailer and the reviews are positive everywhere for this free app. Subset databases within minutes, efficient customer data migration process are just some of the feedback you will find on this excellent app.