This query works on a personal geodatabase:
SELECT GDB_ObjectClasses.ID, GDB_ObjectClasses.Name, GDB_Subtypes.ClassID, GDB_Subtypes.SubtypeCode, GDB_Subtypes.SubtypeName
FROM GDB_ObjectClasses INNER JOIN GDB_Subtypes ON GDB_ObjectClasses.ID = GDB_Subtypes.ClassID;
Syntax in SDe:
SELECT [Owner].GDB_OBJECTCLASSES.ID, [Owner].GDB_OBJECTCLASSES.OWNER, [Owner].GDB_OBJECTCLASSES.NAME, [Owner].GDB_SUBTYPES.CLASSID,
[Owner].GDB_SUBTYPES.SUBTYPECODE, [Owner].GDB_SUBTYPES.SUBTYPENAME
FROM [Owner].GDB_OBJECTCLASSES INNER JOIN
[Owner].GDB_SUBTYPES ON [Owner].GDB_OBJECTCLASSES.ID = [Owner].GDB_SUBTYPES.CLASSID