Considering that most users won't update something when they haven't changed anything, and that it hardly matters for a database whether you changed 1 or several columns in a row, why not just always send an update query to the database, and let the database take care of the details?

UPDATE table_name
   SET column1 = ?, column2 = ?, column3 = ?, column4 = ?
       column5 = ?, column6 = ?, column7 = ?, column8 = ?
 WHERE key = ?
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