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For a detailed explanation on searching issues in Jira, you can check the Searching for Issues tutorial from the Jira documentation.
Search operation can be performed based on parent database custom fields, as well as on child database custom fields.
Basically, to perform an issue search based on a database custom field value, you will use the Issue Navigator:
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After introducing the desired value to search for in the database custom field (as simple text value), and selecting any other needed filters, press the search button.
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