选择语句REF oracle

Create or replace type table1_Type as object ( id integer, dateStart date, etc varchar2(20));-- TYPE TABLE1_TYPE compiledcreate table table1 of table1_type;-- table TABLE1 created.Create or replace type table2_type as object( id integer, items varchar2(30), datePurchased varchar2(20), table1_Ref REF table1_type);-- TYPE TABLE2_TYPE compiledcreate table table2 of table2_type;--table TABLE2 created.INSERT INTO table1 VALUES(table1_Type(1, SYSDATE, 'etc1...'));INSERT INTO table1 VALUES(table1_Type(2, SYSDATE, 'etc2...'));SELECT  REF(t)FROM    table1 tWHERe   id = 1;-- [TST.TABLE1_TYPE]DECLARE    l_table_1_id_1  REF table1_Type;    l_table_1_id_2  REF table1_Type;BEGIN    SELECt  REF(t)    INTO    l_table_1_id_1    FROM    table1 t    WHERe   id = 1;    SELECt  REF(t)    INTO    l_table_1_id_2    FROM    table1 t    WHERe   id = 2;    INSERT INTO table2 VALUES (21, 'item21', SYSDATE, l_table_1_id_1);    INSERT INTO table2 VALUES (22, 'item22', SYSDATE, l_table_1_id_2);END;-- anonymous block completedSELECt COUNT(*) FROM table1;-- 2SELECt COUNT(*) FROM table2;-- 2SELECt * FROM table1;SELECt * FROM table2;SELECt  *FROM    table1 t1JOIN    table2 t2ON      REF(t1) = t2.table1_Ref;