How to change issue assignee to a value from a custom field in JIRA
Purpose
Due to previous requirements, you might have the person assigned to work on an issue in a custom field instead of in the built-in assignee field. The following queries can be used to update the assignee with the value from the custom fie.d
Solution
Find the custom field id that corresponds with the custom field you are using for assignee:
select id, cfname from customfield;
Update the assignee
update jiraissue set assignee = customfieldvalue.stringvalue from customfieldvalue where jiraissue.id = customfieldvalue.issue and customfieldvalue.customfield = <id from above>;
Always back up your data before performing any modifications to the database. If possible, test any alter, insert, update, or delete SQL commands on a staging server first.