• If you write database tools, or query tools, this can be handy.
• Say, for example, the Accounting department asks you for report after report.  You write these reports, but start to get bored writing reports all day. So instead, you give them a query tool where they can easily make their own query to get data on an as-needed basis.

• Data about the database.
• Data about the result set.

• Get this object with the getMetaData() method of the Connection class.
• This tells you a lot about what a database supports.  So if you want to make your program both platform independent and highly optimized, you can find what the database supports, and then run your program conditionally on those values.
• For example, say a union is the best way to write a particular query.  But not all databases support unions.  You can use the supportsUnion() method to see if it supports unions.  If so, you can run a union.  If not, you'll have it perform another, perhaps less efficient query.

• Use this to find the name, type, and width of a column in a ResultSet.
• Use the getMetaData() method of the ResultSet class.

 Example