code: func MergeSchema(lSchema, rSchema Schema) Schema {
  	tmpL := lSchema.Clone()
  	tmpR := rSchema.Clone()
  	ret := NewSchema(append(tmpL.Columns, tmpR.Columns...))
  	ret.SetUniqueKeys(append(tmpL.Keys, tmpR.Keys...))
  	return ret
  }
docs: // MergeSchema will merge two schema into one schema.