code: func (j *baseJoiner) makeShallowJoinRow(isRightJoin bool, inner, outer chunk.Row) {
  	if !isRightJoin {
  		inner, outer = outer, inner
  	}
  	j.shallowRow.ShallowCopyPartialRow(0, inner)
  	j.shallowRow.ShallowCopyPartialRow(inner.Len(), outer)
  }
docs: // makeShallowJoinRow shallow copies `inner` and `outer` into `shallowRow`.