ApplySchema: Allow ALTER DATABASE.

This allows using vtctl ApplySchema to execute ALTER DATABASE across all
shards of a keyspace.

Signed-off-by: Anthony Yeh <enisoc@planetscale.com>

go/test/endtoend/vtgate/schema/schema_test.go

@@ -100,6 +100,7 @@ func TestMain(m *testing.M) {
 func TestSchemaChange(t *testing.T) {
 	testWithInitialSchema(t)
 	testWithAlterSchema(t)
+	testWithAlterDatabase(t)
 	testWithDropCreateSchema(t)
 	testSchemaChangePreflightErrorPartially(t)
 	testDropNonExistentTables(t)
@@ -135,6 +136,13 @@ func testWithAlterSchema(t *testing.T) {
 	matchSchema(t, clusterInstance.Keyspaces[0].Shards[0].Vttablets[0].VttabletProcess.TabletPath, clusterInstance.Keyspaces[0].Shards[1].Vttablets[0].VttabletProcess.TabletPath)
 }
 
+// testWithAlterDatabase tests that ALTER DATABASE is accepted by the validator.
+func testWithAlterDatabase(t *testing.T) {
+	sql := "create database alter_database_test; alter database alter_database_test default character set = utf8mb4; drop database alter_database_test"
+	err := clusterInstance.VtctlclientProcess.ApplySchema(keyspaceName, sql)
+	assert.NoError(t, err)
+}
+
 // testWithDropCreateSchema , we should be able to drop and create same schema
 //Tests that a DROP and CREATE table will pass PreflightSchema check.
 //

go/vt/schemamanager/tablet_executor.go

@@ -101,7 +101,9 @@ func (exec *TabletExecutor) Validate(ctx context.Context, sqls []string) error {
 		return fmt.Errorf("executor is closed")
 	}
 
-	parsedDDLs, err := exec.parseDDLs(sqls)
+	// We ignore DATABASE-level DDLs here because detectBigSchemaChanges doesn't
+	// look at them anyway.
+	parsedDDLs, _, err := exec.parseDDLs(sqls)
 	if err != nil {
 		return err
 	}
@@ -114,23 +116,26 @@ func (exec *TabletExecutor) Validate(ctx context.Context, sqls []string) error {
 	return err
 }
 
-func (exec *TabletExecutor) parseDDLs(sqls []string) ([]*sqlparser.DDL, error) {
-	parsedDDLs := make([]*sqlparser.DDL, 0, len(sqls))
+func (exec *TabletExecutor) parseDDLs(sqls []string) ([]*sqlparser.DDL, []*sqlparser.DBDDL, error) {
+	parsedDDLs := make([]*sqlparser.DDL, 0)
+	parsedDBDDLs := make([]*sqlparser.DBDDL, 0)
 	for _, sql := range sqls {
 		stat, err := sqlparser.Parse(sql)
 		if err != nil {
-			return nil, fmt.Errorf("failed to parse sql: %s, got error: %v", sql, err)
+			return nil, nil, fmt.Errorf("failed to parse sql: %s, got error: %v", sql, err)
 		}
-		ddl, ok := stat.(*sqlparser.DDL)
-		if !ok {
+		switch ddl := stat.(type) {
+		case *sqlparser.DDL:
+			parsedDDLs = append(parsedDDLs, ddl)
+		case *sqlparser.DBDDL:
+			parsedDBDDLs = append(parsedDBDDLs, ddl)
+		default:
 			if len(exec.tablets) != 1 {
-				return nil, fmt.Errorf("non-ddl statements can only be executed for single shard keyspaces: %s", sql)
+				return nil, nil, fmt.Errorf("non-ddl statements can only be executed for single shard keyspaces: %s", sql)
 			}
-			continue
 		}
-		parsedDDLs = append(parsedDDLs, ddl)
 	}
-	return parsedDDLs, nil
+	return parsedDDLs, parsedDBDDLs, nil
 }
 
 // a schema change that satisfies any following condition is considered

go/vt/schemamanager/tablet_executor_test.go

@@ -108,6 +108,8 @@ func TestTabletExecutorValidate(t *testing.T) {
 	sqls := []string{
 		"ALTER TABLE test_table ADD COLUMN new_id bigint(20)",
 		"CREATE TABLE test_table_02 (pk int)",
+		"ALTER DATABASE db_name DEFAULT CHARACTER SET = utf8mb4",
+		"ALTER SCHEMA db_name CHARACTER SET = utf8mb4",
 	}
 
 	if err := executor.Validate(ctx, sqls); err == nil {

go/vt/sqlparser/ast.go

@@ -688,7 +688,7 @@ func (node *Set) walkSubtree(visit Visit) error {
 	)
 }
 
-// DBDDL represents a CREATE, DROP database statement.
+// DBDDL represents a CREATE, DROP, or ALTER database statement.
 type DBDDL struct {
 	Action   string
 	DBName   string
@@ -700,7 +700,7 @@ type DBDDL struct {
 // Format formats the node.
 func (node *DBDDL) Format(buf *TrackedBuffer) {
 	switch node.Action {
-	case CreateStr:
+	case CreateStr, AlterStr:
 		buf.WriteString(fmt.Sprintf("%s database %s", node.Action, node.DBName))
 	case DropStr:
 		exists := ""

go/vt/sqlparser/parse_test.go

@@ -958,6 +958,30 @@ var (
 	}, {
 		input:  "alter table a drop id",
 		output: "alter table a",
+	}, {
+		input:  "alter database d default character set = charset",
+		output: "alter database d",
+	}, {
+		input:  "alter database d character set = charset",
+		output: "alter database d",
+	}, {
+		input:  "alter database d default collate = collation",
+		output: "alter database d",
+	}, {
+		input:  "alter database d collate = collation",
+		output: "alter database d",
+	}, {
+		input:  "alter schema d default character set = charset",
+		output: "alter database d",
+	}, {
+		input:  "alter schema d character set = charset",
+		output: "alter database d",
+	}, {
+		input:  "alter schema d default collate = collation",
+		output: "alter database d",
+	}, {
+		input:  "alter schema d collate = collation",
+		output: "alter database d",
 	}, {
 		input: "create table a",
 	}, {