// ShowTables returns all the tables.
// Privileges: None.
//   Notes: postgres does not have a SHOW TABLES statement.
//          mysql only returns tables you have privileges on.
func (p *planner) ShowTables(n *parser.ShowTables) (planNode, error) {
	// TODO(pmattis): This could be implemented as:
	//
	//   SELECT name FROM system.namespace
	//     WHERE parentID = (SELECT id FROM system.namespace
	//                       WHERE parentID = 0 AND name = <database>)

	name := n.Name
	if name == nil {
		if p.session.Database == "" {
			return nil, errNoDatabase
		}
		name = &parser.QualifiedName{Base: parser.Name(p.session.Database)}
	}
	dbDesc, err := p.getDatabaseDesc(string(name.Base))
	if err != nil {
		return nil, err
	}
	if dbDesc == nil {
		return nil, sqlbase.NewUndefinedDatabaseError(string(name.Base))
	}

	tableNames, err := p.getTableNames(dbDesc)
	if err != nil {
		return nil, err
	}
	v := &valuesNode{columns: []ResultColumn{{Name: "Table", Typ: parser.TypeString}}}
	for _, name := range tableNames {
		v.rows = append(v.rows, []parser.Datum{parser.NewDString(name.Table())})
	}

	return v, nil
}

// getDatabaseID implements the DatabaseAccessor interface.
func (p *planner) getDatabaseID(name string) (sqlbase.ID, error) {
	if id := p.databaseCache.getID(name); id != 0 {
		return id, nil
	}

	// Lookup the database in the cache first, falling back to the KV store if it
	// isn't present. The cache might cause the usage of a recently renamed
	// database, but that's a race that could occur anyways.
	desc, err := p.getCachedDatabaseDesc(name)
	if err != nil {
		if log.V(3) {
			log.Infof("%v", err)
		}
		var err error
		desc, err = p.getDatabaseDesc(name)
		if err != nil {
			return 0, err
		}
		if desc == nil {
			return 0, sqlbase.NewUndefinedDatabaseError(name)
		}
	}

	p.databaseCache.setID(name, desc.ID)
	return desc.ID, nil
}

// expandTableGlob implements the SchemaAccessor interface.
func (p *planner) expandTableGlob(expr *parser.QualifiedName) (
	parser.QualifiedNames, error) {
	if len(expr.Indirect) == 0 {
		return parser.QualifiedNames{expr}, nil
	}

	if err := expr.QualifyWithDatabase(p.session.Database); err != nil {
		return nil, err
	}
	// We must have a single indirect: either .table or .*
	if len(expr.Indirect) != 1 {
		return nil, fmt.Errorf("invalid table glob: %s", expr)
	}

	switch expr.Indirect[0].(type) {
	case parser.NameIndirection:
		return parser.QualifiedNames{expr}, nil
	case parser.StarIndirection:
		dbDesc, err := p.getDatabaseDesc(string(expr.Base))
		if err != nil {
			return nil, err
		}
		if dbDesc == nil {
			return nil, sqlbase.NewUndefinedDatabaseError(string(expr.Base))
		}
		tableNames, err := p.getTableNames(dbDesc)
		if err != nil {
			return nil, err
		}
		return tableNames, nil
	default:
		return nil, fmt.Errorf("invalid table glob: %s", expr)
	}
}

// RenameDatabase renames the database.
// Privileges: security.RootUser user.
//   Notes: postgres requires superuser, db owner, or "CREATEDB".
//          mysql >= 5.1.23 does not allow database renames.
func (p *planner) RenameDatabase(n *parser.RenameDatabase) (planNode, error) {
	if n.Name == "" || n.NewName == "" {
		return nil, errEmptyDatabaseName
	}

	if p.session.User != security.RootUser {
		return nil, fmt.Errorf("only %s is allowed to rename databases", security.RootUser)
	}

	dbDesc, err := p.getDatabaseDesc(string(n.Name))
	if err != nil {
		return nil, err
	}
	if dbDesc == nil {
		return nil, sqlbase.NewUndefinedDatabaseError(string(n.Name))
	}

	if n.Name == n.NewName {
		// Noop.
		return &emptyNode{}, nil
	}

	// Now update the nameMetadataKey and the descriptor.
	descKey := sqlbase.MakeDescMetadataKey(dbDesc.GetID())
	dbDesc.SetName(string(n.NewName))

	if err := dbDesc.Validate(); err != nil {
		return nil, err
	}

	newKey := databaseKey{string(n.NewName)}.Key()
	oldKey := databaseKey{string(n.Name)}.Key()
	descID := dbDesc.GetID()
	descDesc := sqlbase.WrapDescriptor(dbDesc)

	b := client.Batch{}
	b.CPut(newKey, descID, nil)
	b.Put(descKey, descDesc)
	b.Del(oldKey)

	if err := p.txn.Run(&b); err != nil {
		if _, ok := err.(*roachpb.ConditionFailedError); ok {
			return nil, fmt.Errorf("the new database name %q already exists", string(n.NewName))
		}
		return nil, err
	}

	p.setTestingVerifyMetadata(func(systemConfig config.SystemConfig) error {
		if err := expectDescriptorID(systemConfig, newKey, descID); err != nil {
			return err
		}
		if err := expectDescriptor(systemConfig, descKey, descDesc); err != nil {
			return err
		}
		return expectDeleted(systemConfig, oldKey)
	})

	return &emptyNode{}, nil
}

// Set sets session variables.
// Privileges: None.
//   Notes: postgres/mysql do not require privileges for session variables (some exceptions).
func (p *planner) Set(n *parser.Set) (planNode, error) {
	if n.Name == nil {
		// A client has sent the reserved internal syntax SET ROW ...
		// Reject it.
		return nil, errors.New("invalid statement: SET ROW")
	}

	// By using QualifiedName.String() here any variables that are keywords will
	// be double quoted.
	name := strings.ToUpper(n.Name.String())
	typedValues := make([]parser.TypedExpr, len(n.Values))
	for i, expr := range n.Values {
		typedValue, err := parser.TypeCheck(expr, nil, parser.TypeString)
		if err != nil {
			return nil, err
		}
		typedValues[i] = typedValue
	}
	switch name {
	case `DATABASE`:
		dbName, err := p.getStringVal(name, typedValues)
		if err != nil {
			return nil, err
		}
		if len(dbName) != 0 {
			// Verify database descriptor exists.
			dbDesc, err := p.getDatabaseDesc(dbName)
			if err != nil {
				return nil, err
			}
			if dbDesc == nil {
				return nil, sqlbase.NewUndefinedDatabaseError(dbName)
			}
		}
		p.session.Database = dbName

	case `SYNTAX`:
		s, err := p.getStringVal(name, typedValues)
		if err != nil {
			return nil, err
		}
		switch sqlbase.NormalizeName(s) {
		case sqlbase.NormalizeName(parser.Modern.String()):
			p.session.Syntax = int32(parser.Modern)
		case sqlbase.NormalizeName(parser.Traditional.String()):
			p.session.Syntax = int32(parser.Traditional)
		default:
			return nil, fmt.Errorf("%s: \"%s\" is not in (%q, %q)", name, s, parser.Modern, parser.Traditional)
		}

	case `EXTRA_FLOAT_DIGITS`:
		// These settings are sent by the JDBC driver but we silently ignore them.

	default:
		return nil, fmt.Errorf("unknown variable: %q", name)
	}
	return &emptyNode{}, nil
}

// getDatabaseDesc implements the DatabaseAccessor interface.
func (p *planner) mustGetDatabaseDesc(name string) (*sqlbase.DatabaseDescriptor, error) {
	desc, err := p.getDatabaseDesc(name)
	if err != nil {
		return nil, err
	}
	if desc == nil {
		return nil, sqlbase.NewUndefinedDatabaseError(name)
	}
	return desc, nil
}

// getDescriptorsFromTargetList implements the DescriptorAccessor interface.
func (p *planner) getDescriptorsFromTargetList(targets parser.TargetList) (
	[]sqlbase.DescriptorProto, error) {
	if targets.Databases != nil {
		if len(targets.Databases) == 0 {
			return nil, errNoDatabase
		}
		descs := make([]sqlbase.DescriptorProto, 0, len(targets.Databases))
		for _, database := range targets.Databases {
			descriptor, err := p.getDatabaseDesc(database)
			if err != nil {
				return nil, err
			}
			if descriptor == nil {
				return nil, sqlbase.NewUndefinedDatabaseError(database)
			}
			descs = append(descs, descriptor)
		}
		return descs, nil
	}

	if len(targets.Tables) == 0 {
		return nil, errNoTable
	}
	descs := make([]sqlbase.DescriptorProto, 0, len(targets.Tables))
	for _, tableGlob := range targets.Tables {
		tables, err := p.expandTableGlob(tableGlob)
		if err != nil {
			return nil, err
		}
		for _, table := range tables {
			descriptor, err := p.getTableDesc(table)
			if err != nil {
				return nil, err
			}
			if descriptor == nil {
				return nil, sqlbase.NewUndefinedTableError(table.String())
			}
			descs = append(descs, descriptor)
		}
	}
	return descs, nil
}

// getTableDesc implements the SchemaAccessor interface.
func (p *planner) getTableDesc(qname *parser.QualifiedName) (*sqlbase.TableDescriptor, error) {
	if err := qname.NormalizeTableName(p.session.Database); err != nil {
		return nil, err
	}
	dbDesc, err := p.getDatabaseDesc(qname.Database())
	if err != nil {
		return nil, err
	}
	if dbDesc == nil {
		return nil, sqlbase.NewUndefinedDatabaseError(qname.Database())
	}

	desc := sqlbase.TableDescriptor{}
	found, err := p.getDescriptor(tableKey{parentID: dbDesc.ID, name: qname.Table()}, &desc)
	if err != nil {
		return nil, err
	}
	if !found {
		return nil, nil
	}
	return &desc, nil
}

// RenameColumn renames the column.
// Privileges: CREATE on table.
//   notes: postgres requires CREATE on the table.
//          mysql requires ALTER, CREATE, INSERT on the table.
func (p *planner) RenameColumn(n *parser.RenameColumn) (planNode, error) {
	newColName := string(n.NewName)
	if newColName == "" {
		return nil, errEmptyColumnName
	}

	if err := n.Table.NormalizeTableName(p.session.Database); err != nil {
		return nil, err
	}

	dbDesc, err := p.getDatabaseDesc(n.Table.Database())
	if err != nil {
		return nil, err
	}
	if dbDesc == nil {
		return nil, sqlbase.NewUndefinedDatabaseError(n.Table.Database())
	}

	// Check if table exists.
	tbKey := tableKey{dbDesc.ID, n.Table.Table()}.Key()
	gr, err := p.txn.Get(tbKey)
	if err != nil {
		return nil, err
	}
	if !gr.Exists() {
		if n.IfExists {
			// Noop.
			return &emptyNode{}, nil
		}
		// Key does not exist, but we want it to: error out.
		return nil, fmt.Errorf("table %q does not exist", n.Table.Table())
	}

	tableDesc, err := p.getTableDesc(n.Table)
	if err != nil {
		return nil, err
	}
	if tableDesc == nil {
		return nil, sqlbase.NewUndefinedTableError(n.Table.String())
	}

	colName := string(n.Name)
	status, i, err := tableDesc.FindColumnByName(colName)
	// n.IfExists only applies to table, no need to check here.
	if err != nil {
		return nil, err
	}
	var column *sqlbase.ColumnDescriptor
	if status == sqlbase.DescriptorActive {
		column = &tableDesc.Columns[i]
	} else {
		column = tableDesc.Mutations[i].GetColumn()
	}

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

	if sqlbase.EqualName(colName, newColName) {
		// Noop.
		return &emptyNode{}, nil
	}

	if _, _, err := tableDesc.FindColumnByName(newColName); err == nil {
		return nil, fmt.Errorf("column name %q already exists", newColName)
	}

	preFn := func(expr parser.Expr) (err error, recurse bool, newExpr parser.Expr) {
		if qname, ok := expr.(*parser.QualifiedName); ok {
			if err := qname.NormalizeColumnName(); err != nil {
				return err, false, nil
			}
			if qname.Column() == colName {
				qname.Indirect[0] = parser.NameIndirection(newColName)
				qname.ClearString()
			}
			return nil, false, qname
		}
		return nil, true, expr
	}

	exprStrings := make([]string, len(tableDesc.Checks))
	for i, check := range tableDesc.Checks {
		exprStrings[i] = check.Expr
	}
	exprs, err := parser.ParseExprsTraditional(exprStrings)
	if err != nil {
		return nil, err
	}

	for i := range tableDesc.Checks {
		expr, err := parser.SimpleVisit(exprs[i], preFn)
		if err != nil {
			return nil, err
		}
		if after := expr.String(); after != tableDesc.Checks[i].Expr {
//.........这里部分代码省略.........

// RenameTable renames the table.
// Privileges: DROP on source table, CREATE on destination database.
//   Notes: postgres requires the table owner.
//          mysql requires ALTER, DROP on the original table, and CREATE, INSERT
//          on the new table (and does not copy privileges over).
func (p *planner) RenameTable(n *parser.RenameTable) (planNode, error) {
	if err := n.NewName.NormalizeTableName(p.session.Database); err != nil {
		return nil, err
	}

	if n.NewName.Table() == "" {
		return nil, errEmptyTableName
	}

	if err := n.Name.NormalizeTableName(p.session.Database); err != nil {
		return nil, err
	}

	dbDesc, err := p.getDatabaseDesc(n.Name.Database())
	if err != nil {
		return nil, err
	}
	if dbDesc == nil {
		return nil, sqlbase.NewUndefinedDatabaseError(n.Name.Database())
	}

	tbKey := tableKey{dbDesc.ID, n.Name.Table()}.Key()

	// Check if table exists.
	gr, err := p.txn.Get(tbKey)
	if err != nil {
		return nil, err
	}
	if !gr.Exists() {
		if n.IfExists {
			// Noop.
			return &emptyNode{}, nil
		}
		// Key does not exist, but we want it to: error out.
		return nil, fmt.Errorf("table %q does not exist", n.Name.Table())
	}

	targetDbDesc, err := p.getDatabaseDesc(n.NewName.Database())
	if err != nil {
		return nil, err
	}
	if targetDbDesc == nil {
		return nil, sqlbase.NewUndefinedDatabaseError(n.NewName.Database())
	}

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

	if n.Name.Database() == n.NewName.Database() && n.Name.Table() == n.NewName.Table() {
		// Noop.
		return &emptyNode{}, nil
	}

	tableDesc, err := p.getTableDesc(n.Name)
	if err != nil {
		return nil, err
	}
	if tableDesc == nil || tableDesc.State != sqlbase.TableDescriptor_PUBLIC {
		return nil, sqlbase.NewUndefinedTableError(n.Name.String())
	}

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

	tableDesc.SetName(n.NewName.Table())
	tableDesc.ParentID = targetDbDesc.ID

	descKey := sqlbase.MakeDescMetadataKey(tableDesc.GetID())
	newTbKey := tableKey{targetDbDesc.ID, n.NewName.Table()}.Key()

	if err := tableDesc.Validate(); err != nil {
		return nil, err
	}

	descID := tableDesc.GetID()
	descDesc := sqlbase.WrapDescriptor(tableDesc)

	if err := tableDesc.SetUpVersion(); err != nil {
		return nil, err
	}
	renameDetails := sqlbase.TableDescriptor_RenameInfo{
		OldParentID: uint32(dbDesc.ID),
		OldName:     n.Name.Table()}
	tableDesc.Renames = append(tableDesc.Renames, renameDetails)
	if err := p.writeTableDesc(tableDesc); err != nil {
		return nil, err
	}

	// We update the descriptor to the new name, but also leave the mapping of the
	// old name to the id, so that the name is not reused until the schema changer
	// has made sure it's not in use any more.
	b := client.Batch{}
	b.Put(descKey, descDesc)
//.........这里部分代码省略.........

// RenameColumn renames the column.
// Privileges: CREATE on table.
//   notes: postgres requires CREATE on the table.
//          mysql requires ALTER, CREATE, INSERT on the table.
func (p *planner) RenameColumn(n *parser.RenameColumn) (planNode, error) {
	newColName := string(n.NewName)
	if newColName == "" {
		return nil, errEmptyColumnName
	}

	if err := n.Table.NormalizeTableName(p.session.Database); err != nil {
		return nil, err
	}

	dbDesc, err := p.getDatabaseDesc(n.Table.Database())
	if err != nil {
		return nil, err
	}
	if dbDesc == nil {
		return nil, sqlbase.NewUndefinedDatabaseError(n.Table.Database())
	}

	// Check if table exists.
	tbKey := tableKey{dbDesc.ID, n.Table.Table()}.Key()
	gr, err := p.txn.Get(tbKey)
	if err != nil {
		return nil, err
	}
	if !gr.Exists() {
		if n.IfExists {
			// Noop.
			return &emptyNode{}, nil
		}
		// Key does not exist, but we want it to: error out.
		return nil, fmt.Errorf("table %q does not exist", n.Table.Table())
	}

	tableDesc, err := p.getTableDesc(n.Table)
	if err != nil {
		return nil, err
	}
	if tableDesc == nil {
		return nil, sqlbase.NewUndefinedTableError(n.Table.String())
	}

	colName := string(n.Name)
	status, i, err := tableDesc.FindColumnByName(colName)
	// n.IfExists only applies to table, no need to check here.
	if err != nil {
		return nil, err
	}
	var column *sqlbase.ColumnDescriptor
	if status == sqlbase.DescriptorActive {
		column = &tableDesc.Columns[i]
	} else {
		column = tableDesc.Mutations[i].GetColumn()
	}

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

	if sqlbase.EqualName(colName, newColName) {
		// Noop.
		return &emptyNode{}, nil
	}

	if _, _, err := tableDesc.FindColumnByName(newColName); err == nil {
		return nil, fmt.Errorf("column name %q already exists", newColName)
	}

	// Rename the column in the indexes.
	tableDesc.RenameColumn(column.ID, newColName)
	column.Name = newColName
	if err := tableDesc.SetUpVersion(); err != nil {
		return nil, err
	}

	descKey := sqlbase.MakeDescMetadataKey(tableDesc.GetID())
	if err := tableDesc.Validate(); err != nil {
		return nil, err
	}
	if err := p.txn.Put(descKey, sqlbase.WrapDescriptor(tableDesc)); err != nil {
		return nil, err
	}
	p.notifySchemaChange(tableDesc.ID, sqlbase.InvalidMutationID)
	return &emptyNode{}, nil
}