Adds same access method check

src/backend/distributed/commands/alter_table.c

@@ -455,6 +455,14 @@ AlterTableSetAccessMethod(TableConversionParameters *params)
 	params->conversionType = ALTER_TABLE_SET_ACCESS_METHOD;
 	params->shardCountIsNull = true;
 	TableConversionState *con = CreateTableConversion(params);
+
+	if (strcmp(con->originalAccessMethod, con->accessMethod) == 0)
+	{
+		ereport(ERROR, (errmsg("the access method of %s is already %s",
+							   generate_qualified_relation_name(con->relationId),
+							   con->accessMethod)));
+	}
+
 	return ConvertTable(con);
 }
 

src/test/regress/expected/alter_table_set_access_method.out

@@ -455,6 +455,10 @@ NOTICE:  Renaming the new table to alter_table_set_access_method.test_fk_p1
 ERROR:  Foreign keys and AFTER ROW triggers are not supported for columnar tables
 HINT:  Consider an AFTER STATEMENT trigger instead.
 CONTEXT:  SQL statement "ALTER TABLE alter_table_set_access_method.test_fk_p ATTACH PARTITION alter_table_set_access_method.test_fk_p1 FOR VALUES FROM (10) TO (20);"
+-- test changing into same access method
+CREATE TABLE same_access_method (a INT);
+SELECT alter_table_set_access_method('same_access_method', 'heap');
+ERROR:  the access method of alter_table_set_access_method.same_access_method is already heap
 SET client_min_messages TO WARNING;
 DROP SCHEMA alter_table_set_access_method CASCADE;
 SELECT 1 FROM master_remove_node('localhost', :master_port);

src/test/regress/sql/alter_table_set_access_method.sql

@@ -139,6 +139,10 @@ create table test_fk_p0 partition of test_fk_p for values from (0) to (10);
 create table test_fk_p1 partition of test_fk_p for values from (10) to (20);
 select alter_table_set_access_method('test_fk_p1', 'columnar');
 
+-- test changing into same access method
+CREATE TABLE same_access_method (a INT);
+SELECT alter_table_set_access_method('same_access_method', 'heap');
+
 SET client_min_messages TO WARNING;
 DROP SCHEMA alter_table_set_access_method CASCADE;
 SELECT 1 FROM master_remove_node('localhost', :master_port);