code: func (mr MutRow) ShallowCopyPartialRow(colIdx int, row Row) {
  	for i, srcCol := range row.c.columns {
  		dstCol := mr.c.columns[colIdx+i]
  		if !srcCol.isNull(row.idx) {
  			// MutRow only contains one row, so we can directly set the whole byte.
  			dstCol.nullBitmap[0] = 1
  		} else {
  			dstCol.nullBitmap[0] = 0
  		}
  
  		if srcCol.isFixed() {
  			elemLen := len(srcCol.elemBuf)
  			offset := row.idx * elemLen
  			dstCol.data = srcCol.data[offset : offset+elemLen]
  		} else {
  			start, end := srcCol.offsets[row.idx], srcCol.offsets[row.idx+1]
  			dstCol.data = srcCol.data[start:end]
  			dstCol.offsets[1] = int32(len(dstCol.data))
  		}
  	}
  }
docs: // ShallowCopyPartialRow shallow copies the data of `row` to MutRow.