code: func (r *RegionFrameRange) GetIndexFrame(tableID, indexID int64, dbName, tableName, indexName string) *FrameItem {
  	if tableID == r.First.TableID && !r.First.IsRecord && indexID == r.First.IndexID {
  		r.First.DBName, r.First.TableName, r.First.IndexName = dbName, tableName, indexName
  		return r.First
  	}
  	if tableID == r.Last.TableID && indexID == r.Last.IndexID {
  		r.Last.DBName, r.Last.TableName, r.Last.IndexName = dbName, tableName, indexName
  		return r.Last
  	}
  
  	greaterThanFirst := tableID > r.First.TableID || (tableID == r.First.TableID && !r.First.IsRecord && indexID > r.First.IndexID)
  	lessThanLast := tableID < r.Last.TableID || (tableID == r.Last.TableID && (r.Last.IsRecord || indexID < r.Last.IndexID))
  	if greaterThanFirst && lessThanLast {
  		return &FrameItem{
  			DBName:    dbName,
  			TableName: tableName,
  			TableID:   tableID,
  			IsRecord:  false,
  			IndexName: indexName,
  			IndexID:   indexID,
  		}
  	}
  	return nil
  }
docs: // GetIndexFrame returns the indnex frame of a table. If the table's indices are
  // not covered by this frame range, it returns nil.