executor, planner: add SHOW CREATE PLACEMENT POLICY (pingcap#28797)

executor/show.go

@@ -146,6 +146,8 @@ func (e *ShowExec) fetchAll(ctx context.Context) error {
 		return e.fetchShowCreateView()
 	case ast.ShowCreateDatabase:
 		return e.fetchShowCreateDatabase()
+	case ast.ShowCreatePlacementPolicy:
+		return e.fetchShowCreatePlacementPolicy()
 	case ast.ShowDatabases:
 		return e.fetchShowDatabases()
 	case ast.ShowDrainerStatus:
@@ -1380,6 +1382,17 @@ func (e *ShowExec) fetchShowCreateDatabase() error {
 	return nil
 }
 
+// fetchShowCreatePlacementPolicy composes show create policy result.
+func (e *ShowExec) fetchShowCreatePlacementPolicy() error {
+	policy, found := e.is.PolicyByName(e.DBName)
+	if !found {
+		return infoschema.ErrPlacementPolicyNotExists.GenWithStackByArgs(e.DBName.O)
+	}
+	showCreate := fmt.Sprintf("CREATE PLACEMENT POLICY `%s` %s", e.DBName.O, policy.PlacementSettings.String())
+	e.appendRow([]interface{}{e.DBName.O, showCreate})
+	return nil
+}
+
 func (e *ShowExec) fetchShowCollation() error {
 	collations := collate.GetSupportedCollations()
 	for _, v := range collations {

executor/show_test.go

@@ -1415,6 +1415,19 @@ func (s *testSuite5) TestShowPerformanceSchema(c *C) {
 			"events_statements_summary_by_digest 0 SCHEMA_NAME 2 DIGEST A 0 <nil> <nil> YES BTREE   YES <nil> NO"))
 }
 
+func (s *testSuite5) TestShowCreatePlacementPolicy(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("CREATE PLACEMENT POLICY xyz PRIMARY_REGION='us-east-1' REGIONS='us-east-1,us-east-2' FOLLOWERS=4")
+	tk.MustQuery("SHOW CREATE PLACEMENT POLICY xyz").Check(testkit.Rows("xyz CREATE PLACEMENT POLICY `xyz` PRIMARY_REGION=\"us-east-1\" REGIONS=\"us-east-1,us-east-2\" FOLLOWERS=4"))
+	// non existent policy
+	err := tk.QueryToErr("SHOW CREATE PLACEMENT POLICY doesnotexist")
+	c.Assert(err.Error(), Equals, infoschema.ErrPlacementPolicyNotExists.GenWithStackByArgs("doesnotexist").Error())
+	// alter and try second example
+	tk.MustExec("ALTER PLACEMENT POLICY xyz FOLLOWERS=4")
+	tk.MustQuery("SHOW CREATE PLACEMENT POLICY xyz").Check(testkit.Rows("xyz CREATE PLACEMENT POLICY `xyz` FOLLOWERS=4"))
+	tk.MustExec("DROP PLACEMENT POLICY xyz")
+}
+
 func (s *testSuite5) TestShowTemporaryTable(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")

planner/core/planbuilder.go

@@ -4047,6 +4047,8 @@ func buildShowSchema(s *ast.ShowStmt, isView bool, isSequence bool) (schema *exp
 		} else {
 			names = []string{"Table", "Create Table"}
 		}
+	case ast.ShowCreatePlacementPolicy:
+		names = []string{"Policy", "Create Policy"}
 	case ast.ShowCreateUser:
 		if s.User != nil {
 			names = []string{fmt.Sprintf("CREATE USER for %s", s.User)}