Information about an issue is scattered around in multiple tables in the JIRA database. However, a good starting point is the jiraissue table, which is where the issue record is stored. It has foreign keys referencing other tables and, at the same time, the issue ID is referenced in a few other tables.
The following diagram captures the important tables that the jiraissue table has a parent relationship with:
As you can see, critical information about an issue such as the project, issue type, status, priority, resolution, security level, and workflow, are all stored in the respective tables but are referenced from the jiraissue table, using a foreign key. The foreign key points to the ID of the other tables in all cases, but there are no foreign key constraints enforced on any of these tables.
Similarly, the following diagram shows the tables that the jiraissue table has a child relationship with:
Here, the tables customfieldvalue, changegroup...