Here you can find set of easy to use diff & merge utilities for a number of popular database management systems:
These utilities allow a user to compare and merge both data, and database programming objects. The utilities features a native two-panel UI that is commonly used in industry-leading text-diff tools. Here are the most common tools used in all these utilities, using the example of MssqlMerge:
Each utility has Free and Pro version. The free version has basic features covering most of primary DB diff & merge tasks: compare table definitions, table data, primary DB programming objects. Be aware that data diff can have some limitations based on the complexity of table definitions. The pro version has none of these limitations - it has an even more convenient and powerful UI to observe changes, support additional object types, and has a number of tools not available in the free version.