Is this a question about the Jira database? A Confluence database? or some other product?
At least in regards to Jira: These two tables don't contain related elements/fields. So I'm not sure how you would join them for any purpose of use.
You can see from the database schema in https://developer.atlassian.com/server/jira/platform/database-schema/ that these two tables don't relate directly to each other in any way.
Is there something that you are looking for within the database here?
There is no lookup or cross reference, the Atlassian systems that have those tables handle the relationships it needs in its code.
I would want to question what you are trying to achieve, as we can't really tell you where to look in a database without knowing what the actual question is. Plus, we'd like to tell you how to answer the question without reading the database, as it is the single worst possible way to report on any Atlassian system.
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