You can use one of the following available types for the database fields: Using autocomplete and Using select list on a ticket with the option to select multiple values as well.
The Child Database Custom Field is a simple text box, an its value is filled automatically when the value for its parent changes.
The fields are used in the following Jira operations:
Edit an issue
Create an issue
Transitions on issue
In order to depend on each other, both Parent and Child Database Custom Fields should be on the same screen, context.