input: [Option name] table_structure [Option type] string [Example] INGRES_STRUCTURE_BTREE [Description] 
output: The default structure for new tables. Valid values for table_structure are: INGRES_STRUCTURE_BTREE INGRES_STRUCTURE_HASH INGRES_STRUCTURE_HEAP INGRES_STRUCTURE_ISAM INGRES_STRUCTURE_CBTREE INGRES_STRUCTURE_CISAM INGRES_STRUCTURE_CHASH INGRES_STRUCTURE_CHEAP