code: func isRangePartitionColUnsignedBigint(cols []*table.Column, pi *model.PartitionInfo) bool {
  	for _, col := range cols {
  		isUnsigned := col.Tp == mysql.TypeLonglong && mysql.HasUnsignedFlag(col.Flag)
  		if isUnsigned && strings.Contains(strings.ToLower(pi.Expr), col.Name.L) {
  			return true
  		}
  	}
  	return false
  }
docs: // isRangePartitionColUnsignedBigint returns true if the partitioning key column type is unsigned bigint type.