Golang Batch.DelRange方法代碼示例

// deleteRow adds to the batch the kv operations necessary to delete a table row
// with the given values.
func (rd *rowDeleter) deleteRow(b *client.Batch, values []parser.Datum) error {
	if err := rd.fks.checkAll(values); err != nil {
		return err
	}

	primaryIndexKey, secondaryIndexEntries, err := rd.helper.encodeIndexes(rd.fetchColIDtoRowIndex, values)
	if err != nil {
		return err
	}

	for _, secondaryIndexEntry := range secondaryIndexEntries {
		if log.V(2) {
			log.Infof("Del %s", secondaryIndexEntry.Key)
		}
		b.Del(secondaryIndexEntry.Key)
	}

	// Delete the row.
	rd.startKey = roachpb.Key(primaryIndexKey)
	rd.endKey = rd.startKey.PrefixEnd()
	if log.V(2) {
		log.Infof("DelRange %s - %s", rd.startKey, rd.endKey)
	}
	b.DelRange(&rd.startKey, &rd.endKey, false)
	rd.startKey, rd.endKey = nil, nil

	return nil
}

// Truncate deletes all rows from a table.
// Privileges: WRITE on table.
//   Notes: postgres requires TRUNCATE.
//          mysql requires DROP (for mysql >= 5.1.16, DELETE before that).
func (p *planner) Truncate(n *parser.Truncate) (planNode, error) {
	b := client.Batch{}

	for _, tableQualifiedName := range n.Tables {
		tableDesc, err := p.getTableDesc(tableQualifiedName)
		if err != nil {
			return nil, err
		}

		if err := p.checkPrivilege(tableDesc, privilege.WRITE); err != nil {
			return nil, err
		}

		tablePrefix := MakeTablePrefix(tableDesc.ID)

		// Delete rows and indexes starting with the table's prefix.
		tableStartKey := proto.Key(tablePrefix)
		tableEndKey := tableStartKey.PrefixEnd()
		if log.V(2) {
			log.Infof("DelRange %q - %q", tableStartKey, tableEndKey)
		}
		b.DelRange(tableStartKey, tableEndKey)
	}

	if err := p.txn.Run(&b); err != nil {
		return nil, err
	}

	// TODO(tamird/pmattis): return the number of affected rows
	return &valuesNode{}, nil
}

// Truncate deletes all rows from a table.
// Privileges: WRITE on table.
//   Notes: postgres requires TRUNCATE.
//          mysql requires DROP (for mysql >= 5.1.16, DELETE before that).
func (p *planner) Truncate(n *parser.Truncate) (planNode, error) {
	b := client.Batch{}

	for _, tableQualifiedName := range n.Tables {
		tableDesc, err := p.getTableDesc(tableQualifiedName)
		if err != nil {
			return nil, err
		}

		if !tableDesc.HasPrivilege(p.user, parser.PrivilegeWrite) {
			return nil, fmt.Errorf("user %s does not have %s privilege on table %s",
				p.user, parser.PrivilegeWrite, tableDesc.Name)
		}

		tablePrefix := encodeTablePrefix(tableDesc.ID)

		// Delete rows and indexes starting with the table's prefix.
		tableStartKey := proto.Key(tablePrefix)
		tableEndKey := tableStartKey.PrefixEnd()
		if log.V(2) {
			log.Infof("DelRange %q - %q", tableStartKey, tableEndKey)
		}
		b.DelRange(tableStartKey, tableEndKey)
	}

	if err := p.db.Run(&b); err != nil {
		return nil, err
	}

	// TODO(tamird/pmattis): return the number of affected rows
	return &valuesNode{}, nil
}

// Truncate deletes all rows from a table.
// Privileges: DROP on table.
//   Notes: postgres requires TRUNCATE.
//          mysql requires DROP (for mysql >= 5.1.16, DELETE before that).
func (p *planner) Truncate(n *parser.Truncate) (planNode, *roachpb.Error) {
	b := client.Batch{}
	for _, tableQualifiedName := range n.Tables {
		tableDesc, pErr := p.getTableLease(tableQualifiedName)
		if pErr != nil {
			return nil, pErr
		}

		if err := p.checkPrivilege(&tableDesc, privilege.DROP); err != nil {
			return nil, roachpb.NewError(err)
		}

		tablePrefix := keys.MakeTablePrefix(uint32(tableDesc.ID))

		// Delete rows and indexes starting with the table's prefix.
		tableStartKey := roachpb.Key(tablePrefix)
		tableEndKey := tableStartKey.PrefixEnd()
		if log.V(2) {
			log.Infof("DelRange %s - %s", tableStartKey, tableEndKey)
		}
		b.DelRange(tableStartKey, tableEndKey, false)
	}

	if pErr := p.txn.Run(&b); pErr != nil {
		return nil, pErr
	}

	return &emptyNode{}, nil
}

// Truncate deletes all rows from a table.
// Privileges: DROP on table.
//   Notes: postgres requires TRUNCATE.
//          mysql requires DROP (for mysql >= 5.1.16, DELETE before that).
func (p *planner) Truncate(n *parser.Truncate) (planNode, error) {
	b := client.Batch{}
	for _, tableQualifiedName := range n.Tables {
		tableDesc, err := p.getTableDesc(tableQualifiedName)
		if err != nil {
			return nil, err
		}

		if err := p.checkPrivilege(tableDesc, privilege.DROP); err != nil {
			return nil, err
		}

		tablePrefix := keys.MakeTablePrefix(uint32(tableDesc.ID))

		// Delete rows and indexes starting with the table's prefix.
		tableStartKey := proto.Key(tablePrefix)
		tableEndKey := tableStartKey.PrefixEnd()
		if log.V(2) {
			log.Infof("DelRange %s - %s", prettyKey(tableStartKey, 0), prettyKey(tableEndKey, 0))
		}
		b.DelRange(tableStartKey, tableEndKey)
	}

	if err := p.txn.Run(&b); err != nil {
		return nil, err
	}

	return &valuesNode{}, nil
}

// Delete deletes rows from a table.
func (p *planner) Delete(n *parser.Delete) (planNode, error) {
	tableDesc, err := p.getAliasedTableDesc(n.Table)
	if err != nil {
		return nil, err
	}

	// TODO(tamird,pmattis): avoid going through Select to avoid encoding
	// and decoding keys. Also, avoiding Select may provide more
	// convenient access to index keys which we are not currently
	// deleting.
	node, err := p.Select(&parser.Select{
		Exprs: parser.SelectExprs{
			&parser.StarExpr{TableName: parser.QualifiedName{tableDesc.Name}},
		},
		From:  parser.TableExprs{n.Table},
		Where: n.Where,
	})
	if err != nil {
		return nil, err
	}

	colMap := map[uint32]int{}
	for i, name := range node.Columns() {
		c, err := tableDesc.FindColumnByName(name)
		if err != nil {
			return nil, err
		}
		colMap[c.ID] = i
	}

	index := tableDesc.Indexes[0]
	indexKey := encodeIndexKeyPrefix(tableDesc.ID, index.ID)

	b := client.Batch{}

	for node.Next() {
		if err := node.Err(); err != nil {
			return nil, err
		}

		// TODO(tamird/pmattis): delete the secondary indexes too
		primaryKey, err := encodeIndexKey(index, colMap, node.Values(), indexKey)
		if err != nil {
			return nil, err
		}
		rowStartKey := proto.Key(primaryKey)
		b.DelRange(rowStartKey, rowStartKey.PrefixEnd())
	}

	if err := p.db.Run(&b); err != nil {
		return nil, err
	}

	// TODO(tamird/pmattis): return the number of affected rows
	return &valuesNode{}, nil
}

// truncateTable truncates the data of a table.
// It deletes a range of data for the table, which includes the PK and all
// indexes.
func truncateTable(tableDesc *sqlbase.TableDescriptor, txn *client.Txn) error {
	tablePrefix := keys.MakeTablePrefix(uint32(tableDesc.ID))

	// Delete rows and indexes starting with the table's prefix.
	tableStartKey := roachpb.Key(tablePrefix)
	tableEndKey := tableStartKey.PrefixEnd()
	if log.V(2) {
		log.Infof("DelRange %s - %s", tableStartKey, tableEndKey)
	}
	b := client.Batch{}
	b.DelRange(tableStartKey, tableEndKey, false)
	return txn.Run(&b)
}

// Delete deletes rows from a table.
func (p *planner) Delete(n *parser.Delete) (planNode, error) {
	tableDesc, err := p.getAliasedTableDesc(n.Table)
	if err != nil {
		return nil, err
	}

	// TODO(tamird,pmattis): avoid going through Select to avoid encoding
	// and decoding keys. Also, avoiding Select may provide more
	// convenient access to index keys which we are not currently
	// deleting.
	node, err := p.Select(&parser.Select{
		Exprs: parser.SelectExprs{
			&parser.StarExpr{TableName: parser.QualifiedName{tableDesc.Name}},
		},
		From:  parser.TableExprs{n.Table},
		Where: n.Where,
	})
	if err != nil {
		return nil, err
	}

	colMap := map[uint32]int{}
	for i, name := range node.Columns() {
		c, err := tableDesc.FindColumnByName(name)
		if err != nil {
			return nil, err
		}
		colMap[c.ID] = i
	}

	primaryIndex := tableDesc.Indexes[0]
	primaryIndexKeyPrefix := encodeIndexKeyPrefix(tableDesc.ID, primaryIndex.ID)

	b := client.Batch{}

	for node.Next() {
		if err := node.Err(); err != nil {
			return nil, err
		}
		values := node.Values()

		primaryIndexKeySuffix, err := encodeIndexKey(primaryIndex, colMap, values, nil)
		if err != nil {
			return nil, err
		}
		primaryIndexKey := bytes.Join([][]byte{primaryIndexKeyPrefix, primaryIndexKeySuffix}, nil)

		// Delete the secondary indexes.
		secondaryIndexEntries, err := encodeSecondaryIndexes(tableDesc, colMap, values, primaryIndexKeySuffix)
		if err != nil {
			return nil, err
		}

		for _, secondaryIndexEntry := range secondaryIndexEntries {
			if log.V(2) {
				log.Infof("Del %q", secondaryIndexEntry.key)
			}
			b.Del(secondaryIndexEntry.key)
		}

		// Delete the row.
		rowStartKey := proto.Key(primaryIndexKey)
		rowEndKey := rowStartKey.PrefixEnd()
		if log.V(2) {
			log.Infof("DelRange %q - %q", rowStartKey, rowEndKey)
		}
		b.DelRange(rowStartKey, rowEndKey)
	}

	if err := p.db.Run(&b); err != nil {
		return nil, err
	}

	// TODO(tamird/pmattis): return the number of affected rows
	return &valuesNode{}, nil
}

// Delete deletes rows from a table.
// Privileges: DELETE and SELECT on table. We currently always use a SELECT statement.
//   Notes: postgres requires DELETE. Also requires SELECT for "USING" and "WHERE" with tables.
//          mysql requires DELETE. Also requires SELECT if a table is used in the "WHERE" clause.
func (p *planner) Delete(n *parser.Delete) (planNode, *roachpb.Error) {
	tableDesc, pErr := p.getAliasedTableLease(n.Table)
	if pErr != nil {
		return nil, pErr
	}

	if err := p.checkPrivilege(tableDesc, privilege.DELETE); err != nil {
		return nil, roachpb.NewError(err)
	}

	// TODO(tamird,pmattis): avoid going through Select to avoid encoding
	// and decoding keys.
	rows, pErr := p.Select(&parser.Select{
		Exprs: tableDesc.allColumnsSelector(),
		From:  parser.TableExprs{n.Table},
		Where: n.Where,
	})
	if pErr != nil {
		return nil, pErr
	}

	if p.prepareOnly {
		return nil, nil
	}

	// Construct a map from column ID to the index the value appears at within a
	// row.
	colIDtoRowIndex, err := makeColIDtoRowIndex(rows, tableDesc)
	if err != nil {
		return nil, roachpb.NewError(err)
	}

	primaryIndex := tableDesc.PrimaryIndex
	primaryIndexKeyPrefix := MakeIndexKeyPrefix(tableDesc.ID, primaryIndex.ID)

	b := client.Batch{}
	result := &valuesNode{}
	for rows.Next() {
		rowVals := rows.Values()
		result.rows = append(result.rows, parser.DTuple(nil))

		primaryIndexKey, _, err := encodeIndexKey(
			&primaryIndex, colIDtoRowIndex, rowVals, primaryIndexKeyPrefix)
		if err != nil {
			return nil, roachpb.NewError(err)
		}

		// Delete the secondary indexes.
		indexes := tableDesc.Indexes
		// Also include all the indexes under mutation; mutation state is
		// irrelevant for deletions.
		for _, m := range tableDesc.Mutations {
			if index := m.GetIndex(); index != nil {
				indexes = append(indexes, *index)
			}
		}
		secondaryIndexEntries, err := encodeSecondaryIndexes(
			tableDesc.ID, indexes, colIDtoRowIndex, rowVals)
		if err != nil {
			return nil, roachpb.NewError(err)
		}

		for _, secondaryIndexEntry := range secondaryIndexEntries {
			if log.V(2) {
				log.Infof("Del %s", secondaryIndexEntry.key)
			}
			b.Del(secondaryIndexEntry.key)
		}

		// Delete the row.
		rowStartKey := roachpb.Key(primaryIndexKey)
		rowEndKey := rowStartKey.PrefixEnd()
		if log.V(2) {
			log.Infof("DelRange %s - %s", rowStartKey, rowEndKey)
		}
		b.DelRange(rowStartKey, rowEndKey)
	}

	if pErr := rows.PErr(); pErr != nil {
		return nil, pErr
	}

	if isSystemConfigID(tableDesc.GetID()) {
		// Mark transaction as operating on the system DB.
		p.txn.SetSystemConfigTrigger()
	}
	if pErr := p.txn.Run(&b); pErr != nil {
		return nil, pErr
	}

	return result, nil
}

func (p *planner) backfillBatch(b *client.Batch, tableName *parser.QualifiedName, oldTableDesc, newTableDesc *TableDescriptor) error {
	table := &parser.AliasedTableExpr{Expr: tableName}
	var droppedColumnDescs []ColumnDescriptor
	var droppedIndexDescs []IndexDescriptor
	var newIndexDescs []IndexDescriptor
	for _, m := range oldTableDesc.Mutations {
		switch m.Direction {
		case DescriptorMutation_ADD:
			switch t := m.Descriptor_.(type) {
			case *DescriptorMutation_Column:
				// TODO(vivek): Add column to new columns and use it
				// to fill in default values.

			case *DescriptorMutation_Index:
				newIndexDescs = append(newIndexDescs, *t.Index)
			}

		case DescriptorMutation_DROP:
			switch t := m.Descriptor_.(type) {
			case *DescriptorMutation_Column:
				droppedColumnDescs = append(droppedColumnDescs, *t.Column)

			case *DescriptorMutation_Index:
				droppedIndexDescs = append(droppedIndexDescs, *t.Index)
			}
		}
	}

	if len(droppedColumnDescs) > 0 {
		var updateExprs parser.UpdateExprs
		for _, droppedColumnDesc := range droppedColumnDescs {
			updateExprs = append(updateExprs, &parser.UpdateExpr{
				Names: parser.QualifiedNames{&parser.QualifiedName{Base: parser.Name(droppedColumnDesc.Name)}},
				Expr:  parser.DNull,
			})
		}

		// Run `UPDATE <table> SET col1 = NULL, col2 = NULL, ...` to clear
		// the data stored in the columns being dropped.
		if _, err := p.Update(&parser.Update{
			Table: table,
			Exprs: updateExprs,
		}); err != nil {
			return err
		}
	}

	for _, indexDescriptor := range droppedIndexDescs {
		indexPrefix := MakeIndexKeyPrefix(newTableDesc.ID, indexDescriptor.ID)

		// Delete the index.
		indexStartKey := roachpb.Key(indexPrefix)
		indexEndKey := indexStartKey.PrefixEnd()
		if log.V(2) {
			log.Infof("DelRange %s - %s", prettyKey(indexStartKey, 0), prettyKey(indexEndKey, 0))
		}
		b.DelRange(indexStartKey, indexEndKey)
	}

	if len(newIndexDescs) > 0 {
		// Get all the rows affected.
		// TODO(vivek): Avoid going through Select.
		// TODO(tamird): Support partial indexes?
		rows, err := p.Select(&parser.Select{
			Exprs: parser.SelectExprs{parser.StarSelectExpr()},
			From:  parser.TableExprs{table},
		})
		if err != nil {
			return err
		}

		// Construct a map from column ID to the index the value appears at within a
		// row.
		colIDtoRowIndex, err := makeColIDtoRowIndex(rows, oldTableDesc)
		if err != nil {
			return err
		}

		// TODO(tamird): This will fall down in production use. We need to do
		// something better (see #2036). In particular, this implementation
		// has the following problems:
		// - Very large tables will generate an enormous batch here. This
		// isn't really a problem in itself except that it will exacerbate
		// the other issue:
		// - Any non-quiescent table that this runs against will end up with
		// an inconsistent index. This is because as inserts/updates continue
		// to roll in behind this operation's read front, the written index
		// will become incomplete/stale before it's written.

		for rows.Next() {
			rowVals := rows.Values()

			for _, newIndexDesc := range newIndexDescs {
				secondaryIndexEntries, err := encodeSecondaryIndexes(
					oldTableDesc.ID, []IndexDescriptor{newIndexDesc}, colIDtoRowIndex, rowVals)
				if err != nil {
					return err
				}

				for _, secondaryIndexEntry := range secondaryIndexEntries {
//.........這裏部分代碼省略.........

// Delete deletes rows from a table.
// Privileges: WRITE and READ on table. We currently always use a SELECT statement.
//   Notes: postgres requires DELETE. Also requires SELECT for "USING" and "WHERE" with tables.
//          mysql requires DELETE. Also requires SELECT if a table is used in the "WHERE" clause.
func (p *planner) Delete(n *parser.Delete) (planNode, error) {
	tableDesc, err := p.getAliasedTableDesc(n.Table)
	if err != nil {
		return nil, err
	}

	if !tableDesc.HasPrivilege(p.user, parser.PrivilegeWrite) {
		return nil, fmt.Errorf("user %s does not have %s privilege on table %s",
			p.user, parser.PrivilegeWrite, tableDesc.Name)
	}

	// TODO(tamird,pmattis): avoid going through Select to avoid encoding
	// and decoding keys. Also, avoiding Select may provide more
	// convenient access to index keys which we are not currently
	// deleting.
	node, err := p.Select(&parser.Select{
		Exprs: parser.SelectExprs{
			&parser.StarExpr{TableName: &parser.QualifiedName{Base: parser.Name(tableDesc.Name)}},
		},
		From:  parser.TableExprs{n.Table},
		Where: n.Where,
	})
	if err != nil {
		return nil, err
	}

	// Construct a map from column ID to the index the value appears at within a
	// row.
	colIDtoRowIndex := map[structured.ID]int{}
	for i, name := range node.Columns() {
		c, err := tableDesc.FindColumnByName(name)
		if err != nil {
			return nil, err
		}
		colIDtoRowIndex[c.ID] = i
	}

	primaryIndex := tableDesc.PrimaryIndex
	primaryIndexKeyPrefix := structured.MakeIndexKeyPrefix(tableDesc.ID, primaryIndex.ID)

	b := client.Batch{}

	for node.Next() {
		if err := node.Err(); err != nil {
			return nil, err
		}
		values := node.Values()

		primaryIndexKeySuffix, _, err := encodeIndexKey(primaryIndex.ColumnIDs, colIDtoRowIndex, values, nil)
		if err != nil {
			return nil, err
		}
		primaryIndexKey := bytes.Join([][]byte{primaryIndexKeyPrefix, primaryIndexKeySuffix}, nil)

		// Delete the secondary indexes.
		secondaryIndexEntries, err := encodeSecondaryIndexes(tableDesc.ID, tableDesc.Indexes, colIDtoRowIndex, values, primaryIndexKeySuffix)
		if err != nil {
			return nil, err
		}

		for _, secondaryIndexEntry := range secondaryIndexEntries {
			if log.V(2) {
				log.Infof("Del %q", secondaryIndexEntry.key)
			}
			b.Del(secondaryIndexEntry.key)
		}

		// Delete the row.
		rowStartKey := proto.Key(primaryIndexKey)
		rowEndKey := rowStartKey.PrefixEnd()
		if log.V(2) {
			log.Infof("DelRange %q - %q", rowStartKey, rowEndKey)
		}
		b.DelRange(rowStartKey, rowEndKey)
	}

	if err := p.db.Run(&b); err != nil {
		return nil, err
	}

	// TODO(tamird/pmattis): return the number of affected rows
	return &valuesNode{}, nil
}

func (p *planner) backfillBatch(b *client.Batch, oldTableDesc *TableDescriptor, mutationID MutationID) *roachpb.Error {
	var droppedColumnDescs []ColumnDescriptor
	var droppedIndexDescs []IndexDescriptor
	var newIndexDescs []IndexDescriptor
	// Collect the elements that are part of the mutation.
	for _, m := range oldTableDesc.Mutations {
		if m.MutationID != mutationID {
			// Mutations are applied in a FIFO order. Only apply the first set of
			// mutations if they have the mutation ID we're looking for.
			break
		}
		switch m.Direction {
		case DescriptorMutation_ADD:
			switch t := m.Descriptor_.(type) {
			case *DescriptorMutation_Column:
				// TODO(vivek): Add column to new columns and use it
				// to fill in default values.

			case *DescriptorMutation_Index:
				newIndexDescs = append(newIndexDescs, *t.Index)
			}

		case DescriptorMutation_DROP:
			switch t := m.Descriptor_.(type) {
			case *DescriptorMutation_Column:
				droppedColumnDescs = append(droppedColumnDescs, *t.Column)

			case *DescriptorMutation_Index:
				droppedIndexDescs = append(droppedIndexDescs, *t.Index)
			}
		}
	}

	// TODO(vivek): Break these backfill operations into chunks. All of them
	// will fail on big tables (see #3274).

	// Delete the entire dropped columns.
	// This used to use SQL UPDATE in the past to update the dropped
	// column to NULL; but a column in the process of being
	// dropped is placed in the table descriptor mutations, and
	// a SQL UPDATE of a column in mutations will fail.
	if len(droppedColumnDescs) > 0 {
		// Run a scan across the table using the primary key.
		start := roachpb.Key(MakeIndexKeyPrefix(oldTableDesc.ID, oldTableDesc.PrimaryIndex.ID))
		// Use a different batch to perform the scan.
		batch := &client.Batch{}
		batch.Scan(start, start.PrefixEnd(), 0)
		if pErr := p.txn.Run(batch); pErr != nil {
			return pErr
		}
		for _, result := range batch.Results {
			var sentinelKey roachpb.Key
			for _, kv := range result.Rows {
				if sentinelKey == nil || !bytes.HasPrefix(kv.Key, sentinelKey) {
					// Sentinel keys have a 0 suffix indicating 0 bytes of column
					// ID. Strip off that suffix to determine the prefix shared with the
					// other keys for the row.
					sentinelKey = stripColumnIDLength(kv.Key)
					for _, columnDesc := range droppedColumnDescs {
						// Delete the dropped column.
						colKey := keys.MakeColumnKey(sentinelKey, uint32(columnDesc.ID))
						if log.V(2) {
							log.Infof("Del %s", colKey)
						}
						b.Del(colKey)
					}
				}
			}
		}
	}

	for _, indexDescriptor := range droppedIndexDescs {
		indexPrefix := MakeIndexKeyPrefix(oldTableDesc.ID, indexDescriptor.ID)

		// Delete the index.
		indexStartKey := roachpb.Key(indexPrefix)
		indexEndKey := indexStartKey.PrefixEnd()
		if log.V(2) {
			log.Infof("DelRange %s - %s", indexStartKey, indexEndKey)
		}
		b.DelRange(indexStartKey, indexEndKey)
	}

	if len(newIndexDescs) > 0 {
		// Get all the rows affected.
		// TODO(vivek): Avoid going through Select.
		// TODO(tamird): Support partial indexes?
		// Use a scanNode with SELECT to pass in a TableDescriptor
		// to the SELECT without needing to use a parser.QualifiedName,
		// because we want to run schema changes from a gossip feed of
		// table IDs.
		scan := &scanNode{
			planner: p,
			txn:     p.txn,
			desc:    oldTableDesc,
		}
		scan.initDescDefaults()
		rows, pErr := p.selectIndex(&selectNode{}, scan, nil, false)
		if pErr != nil {
			return pErr
//.........這裏部分代碼省略.........

func (p *planner) backfillBatch(b *client.Batch, oldTableDesc, newTableDesc *TableDescriptor) error {
	var droppedColumnDescs []ColumnDescriptor
	var droppedIndexDescs []IndexDescriptor
	var newIndexDescs []IndexDescriptor
	for _, m := range oldTableDesc.Mutations {
		switch m.Direction {
		case DescriptorMutation_ADD:
			switch t := m.Descriptor_.(type) {
			case *DescriptorMutation_Column:
				// TODO(vivek): Add column to new columns and use it
				// to fill in default values.

			case *DescriptorMutation_Index:
				newIndexDescs = append(newIndexDescs, *t.Index)
			}

		case DescriptorMutation_DROP:
			switch t := m.Descriptor_.(type) {
			case *DescriptorMutation_Column:
				droppedColumnDescs = append(droppedColumnDescs, *t.Column)

			case *DescriptorMutation_Index:
				droppedIndexDescs = append(droppedIndexDescs, *t.Index)
			}
		}
	}

	// TODO(vivek): Break these backfill operations into chunks. All of them
	// will fail on big tables.

	// Delete the entire dropped columns.
	// This used to use SQL UPDATE in the past to update the dropped
	// column to NULL; but a column in the process of being
	// dropped is placed in the table descriptor mutations, and
	// a SQL UPDATE of a column in mutations will fail.
	if len(droppedColumnDescs) > 0 {
		// Run a scan across the table using the primary key.
		start := roachpb.Key(MakeIndexKeyPrefix(newTableDesc.ID, newTableDesc.PrimaryIndex.ID))
		// Use a different batch to perform the scan.
		batch := &client.Batch{}
		batch.Scan(start, start.PrefixEnd(), 0)
		if err := p.txn.Run(batch); err != nil {
			return err
		}
		for _, result := range batch.Results {
			var sentinelKey roachpb.Key
			for _, kv := range result.Rows {
				if sentinelKey == nil || !bytes.HasPrefix(kv.Key, sentinelKey) {
					// Sentinel keys have a 0 suffix indicating 0 bytes of column
					// ID. Strip off that suffix to determine the prefix shared with the
					// other keys for the row.
					sentinelKey = stripColumnIDLength(kv.Key)
					for _, columnDesc := range droppedColumnDescs {
						// Delete the dropped column.
						colKey := keys.MakeColumnKey(sentinelKey, uint32(columnDesc.ID))
						if log.V(2) {
							log.Infof("Del %s", colKey)
						}
						b.Del(colKey)
					}
				}
			}
		}
	}

	for _, indexDescriptor := range droppedIndexDescs {
		indexPrefix := MakeIndexKeyPrefix(newTableDesc.ID, indexDescriptor.ID)

		// Delete the index.
		indexStartKey := roachpb.Key(indexPrefix)
		indexEndKey := indexStartKey.PrefixEnd()
		if log.V(2) {
			log.Infof("DelRange %s - %s", indexStartKey, indexEndKey)
		}
		b.DelRange(indexStartKey, indexEndKey)
	}

	if len(newIndexDescs) > 0 {
		// Get all the rows affected.
		// TODO(vivek): Avoid going through Select.
		// TODO(tamird): Support partial indexes?
		// Use a scanNode with SELECT to pass in a TableDescriptor
		// to the SELECT without needing to use a parser.QualifiedName,
		// because we want to run schema changes from a gossip feed of
		// table IDs.
		scan := &scanNode{
			planner: p,
			txn:     p.txn,
			desc:    oldTableDesc,
		}
		scan.initDescDefaults()
		rows, err := p.selectWithScan(scan, &parser.Select{Exprs: oldTableDesc.allColumnsSelector()})
		if err != nil {
			return err
		}

		// Construct a map from column ID to the index the value appears at within a
		// row.
		colIDtoRowIndex, err := makeColIDtoRowIndex(rows, oldTableDesc)
		if err != nil {
//.........這裏部分代碼省略.........

// DropIndex drops an index.
// Privileges: CREATE on table.
//   Notes: postgres allows only the index owner to DROP an index.
//          mysql requires the INDEX privilege on the table.
func (p *planner) DropIndex(n *parser.DropIndex) (planNode, error) {
	var b client.Batch

	for _, indexQualifiedName := range n.Names {
		if err := indexQualifiedName.NormalizeTableName(p.session.Database); err != nil {
			return nil, err
		}

		tableDesc, err := p.getTableDesc(indexQualifiedName)
		if err != nil {
			return nil, err
		}

		idxName := indexQualifiedName.Index()
		idx, err := tableDesc.FindIndexByName(idxName)
		if err != nil {
			if n.IfExists {
				// Noop.
				return &valuesNode{}, nil
			}
			// Index does not exist, but we want it to: error out.
			return nil, fmt.Errorf("index %q does not exist", idxName)
		}

		if err := p.checkPrivilege(tableDesc, privilege.CREATE); err != nil {
			return nil, err
		}

		indexPrefix := MakeIndexKeyPrefix(tableDesc.ID, idx.ID)

		// Delete the index.
		indexStartKey := proto.Key(indexPrefix)
		indexEndKey := indexStartKey.PrefixEnd()
		if log.V(2) {
			log.Infof("DelRange %q - %q", indexStartKey, indexEndKey)
		}
		b.DelRange(indexStartKey, indexEndKey)

		found := false
		for i := range tableDesc.Indexes {
			if &tableDesc.Indexes[i] == idx {
				tableDesc.Indexes = append(tableDesc.Indexes[:i], tableDesc.Indexes[i+1:]...)
				found = true
				break
			}
		}
		if !found {
			return nil, util.Errorf("index %s not found in %s", idx, tableDesc)
		}

		descKey := MakeDescMetadataKey(tableDesc.GetID())
		if err := tableDesc.Validate(); err != nil {
			return nil, err
		}
		if err := p.txn.Put(descKey, tableDesc); err != nil {
			return nil, err
		}

		// Mark transaction as operating on the system DB.
		p.txn.SetSystemDBTrigger()
	}

	if err := p.txn.Run(&b).GoError(); err != nil {
		return nil, err
	}

	return &valuesNode{}, nil
}

// Delete deletes rows from a table.
// Privileges: DELETE and SELECT on table. We currently always use a SELECT statement.
//   Notes: postgres requires DELETE. Also requires SELECT for "USING" and "WHERE" with tables.
//          mysql requires DELETE. Also requires SELECT if a table is used in the "WHERE" clause.
func (p *planner) Delete(n *parser.Delete) (planNode, error) {
	tableDesc, err := p.getAliasedTableDesc(n.Table, false /* !allowCache */)
	if err != nil {
		return nil, err
	}

	if err := p.checkPrivilege(tableDesc, privilege.DELETE); err != nil {
		return nil, err
	}

	// TODO(tamird,pmattis): avoid going through Select to avoid encoding
	// and decoding keys. Also, avoiding Select may provide more
	// convenient access to index keys which we are not currently
	// deleting.
	rows, err := p.Select(&parser.Select{
		Exprs: parser.SelectExprs{parser.StarSelectExpr()},
		From:  parser.TableExprs{n.Table},
		Where: n.Where,
	})
	if err != nil {
		return nil, err
	}

	// Construct a map from column ID to the index the value appears at within a
	// row.
	colIDtoRowIndex := map[ColumnID]int{}
	for i, name := range rows.Columns() {
		c, err := tableDesc.FindColumnByName(name)
		if err != nil {
			return nil, err
		}
		colIDtoRowIndex[c.ID] = i
	}

	primaryIndex := tableDesc.PrimaryIndex
	primaryIndexKeyPrefix := MakeIndexKeyPrefix(tableDesc.ID, primaryIndex.ID)

	b := client.Batch{}
	result := &valuesNode{}
	for rows.Next() {
		rowVals := rows.Values()
		result.rows = append(result.rows, parser.DTuple(nil))

		primaryIndexKey, _, err := encodeIndexKey(
			primaryIndex.ColumnIDs, colIDtoRowIndex, rowVals, primaryIndexKeyPrefix)
		if err != nil {
			return nil, err
		}

		// Delete the secondary indexes.
		secondaryIndexEntries, err := encodeSecondaryIndexes(
			tableDesc.ID, tableDesc.Indexes, colIDtoRowIndex, rowVals)
		if err != nil {
			return nil, err
		}

		for _, secondaryIndexEntry := range secondaryIndexEntries {
			if log.V(2) {
				log.Infof("Del %s", prettyKey(secondaryIndexEntry.key, 0))
			}
			b.Del(secondaryIndexEntry.key)
		}

		// Delete the row.
		rowStartKey := roachpb.Key(primaryIndexKey)
		rowEndKey := rowStartKey.PrefixEnd()
		if log.V(2) {
			log.Infof("DelRange %s - %s", prettyKey(rowStartKey, 0), prettyKey(rowEndKey, 0))
		}
		b.DelRange(rowStartKey, rowEndKey)
	}

	if err := rows.Err(); err != nil {
		return nil, err
	}

	if err := p.txn.Run(&b); err != nil {
		return nil, err
	}

	return result, nil
}