HedgeDoc 1.x stores notes with a UUID in the database (column id). However, the note URL is generated from that UUID but not stored in the database itself.
When looking for a specific note in the database, this tool can help you convert the note URL to the UUID and vice-versa.
Please note: This tool only works for URLs to the edit page of a note. It does not support shortids (URL from the publish page) nor user-chosen aliases in FreeURL mode.
For these, look into the shortid or alias database columns.