The Magento Database Repair Tool compares 2 databases (reference and target), and updates the target database so it has the same structure as the reference database by doing the following:

• Adds missing tables, or repairs them to have the same engine type and char-set.
• Adds missing fields or repairs them.
• Removes inconsistent data from tables that have broken foreign key references.
• Adds missing foreign keys and indexes.

You can download it here. For a full list of features and instructions, you can refer to this wiki post.