Power Database Fields PRO™ enables you to import data from an external database into a database custom field in your Jira. You can execute any types of queries to the database. When data is retrieved, you select it from a set of results as a select list or autocomplete box. We also provide an Admin page where you can associate queries with the necessary Jira fields.
You can execute any type of query, but the results will be displayed in Jira only for a select statement.
The old documentation (for version 3.0) can be downloaded from here.