我写了一些代码，将禁用和启用表上的外键。它看起来运行良好。当我立即执行代码检查外键的状态时，状态似乎在一个查询中没有改变，而在另一个查询中改变了。
我似乎不能找出问题是什么，希望有人能帮助我，并解释这个异常和/或建议修复我的代码。
下面是我的测试用例沿着示例数据，以显示我所做的工作。

CREATE TABLE customers 
(CUSTOMER_ID, FIRST_NAME, LAST_NAME) AS
SELECT 1, 'Faith', 'Mazzarone' FROM DUAL UNION ALL
SELECT 2, 'Lisa', 'Saladino' FROM DUAL UNION ALL
SELECT 3, 'Micheal', 'Palmice' FROM DUAL UNION ALL
SELECT 4, 'Joseph', 'Zaza' FROM DUAL UNION ALL
SELECT 5, 'Jerry', 'Torchiano' FROM DUAL;

ALTER TABLE customers 
ADD CONSTRAINT customers_pk PRIMARY KEY (customer_id);

CREATE TABLE items 
(PRODUCT_ID, PRODUCT_NAME, PRICE) AS
SELECT 100, 'Black Shoes', 79.99 FROM DUAL UNION ALL
SELECT 101, 'Brown Pants', 111.99 FROM DUAL UNION ALL
SELECT 102, 'White Shirt', 10.99 FROM DUAL;

ALTER TABLE items 
ADD CONSTRAINT items_pk PRIMARY KEY (product_id);

create table purchases(
  ORDER_ID NUMBER GENERATED BY DEFAULT AS IDENTITY (START WITH 1) NOT NULL,
  customer_id   number, 
  PRODUCT_ID NUMBER, 
  QUANTITY NUMBER, 
  purchase_date timestamp
);

insert  into purchases (customer_id, product_id, quantity, purchase_date) 
SELECT 3, 102, 4,TIMESTAMP '2022-12-22 21:44:35' + NUMTODSINTERVAL ( LEVEL * 2, 'DAY') FROM    dual
CONNECT BY  LEVEL <= 15 UNION ALL 
select 1, 101,3, date '2023-03-29' + level * interval '2' day from dual
          connect by level <= 12
union all
select 2, 101,2, date '2023-01-15' + level * interval '8' hour from dual
          connect by level <= 15
union all
select 2, 102,2,date '2023-04-13' + level * interval '1 1' day to hour from dual
          connect by level <= 11
union all
select 3, 101,2, date '2023-02-01' + level * interval '1 05:03' day to minute from dual
          connect by level <= 10
union all
select 3, 101,1, date '2023-04-22' + level * interval '23' hour from dual
          connect by level <= 23
union all
select 3, 100,1,  date '2022-03-01' + level * interval '1 00:23:05' day to second from dual
          connect by level <= 15
union all
select 4, 102,1, date '2023-01-01' + level * interval '5' hour from dual
          connect by level <= 60;

ALTER TABLE purchases 
ADD CONSTRAINT order_pk PRIMARY KEY (order_id);

ALTER TABLE purchases ADD CONSTRAINT customers_fk FOREIGN KEY (customer_id) REFERENCES customers(customer_id);

ALTER TABLE purchases ADD CONSTRAINT items_fk FOREIGN KEY (PRODUCT_ID) REFERENCES items(product_id);

/* both queries fine here */

SELECT '"' || a.owner
                    || '"."'
                    || a.table_name
                    || '"' AS full_table_name,
                a.constraint_name,
                b.status
            FROM user_constraints a
            JOIN user_constraints b
                ON ( a.r_constraint_name = b.constraint_name
                    AND a.r_owner = b.owner )
            WHERE a.constraint_type = 'R'
                AND b.status = 'ENABLED'
            ORDER BY 1

FULL_TABLE_NAME
    CONSTRAINT_NAME STATUS
"XXX"."PURCHASES"   ITEMS_FK    ENABLED
"XXX"."PURCHASES"   CUSTOMERS_FK    ENABLED

select owner, table_name, r_constraint_name, status
 from user_constraints
where constraint_type = 'R';

OWNER   TABLE_NAME  R_CONSTRAINT_NAME   STATUS
XXX PURCHASES   CUSTOMERS_PK    ENABLED
XXX PURCHASES   ITEMS_PK    ENABLED

/* disable foreign keys */

BEGIN
    FOR r IN (
        SELECT '"' || a.owner
                    || '"."'
                    || a.table_name
                    || '"' AS full_table_name,
                a.constraint_name
            FROM user_constraints a
            JOIN user_constraints b
                ON ( a.r_constraint_name = b.constraint_name
                    AND a.r_owner = b.owner )
            WHERE a.constraint_type = 'R'
                AND b.status = 'ENABLED'
            ORDER BY 1 )  LOOP
            
        dbms_output.put_line ( 'Disable the constraint ' || r.constraint_name ||' (on table ' || r.full_table_name || ')' ) ;
        dbms_utility.exec_ddl_statement ( 'alter table ' || r.full_table_name || ' disable constraint ' || r.constraint_name ) ;
        
    END LOOP ;
END ;
/

Statement processed.
Disable the constraint ITEMS_FK (on table "XXX"."PURCHASES")
Disable the constraint CUSTOMERS_FK (on table "XXX"."PURCHASES")

/* status different between queries ????. Problem here!!!
*/

SELECT '"' || a.owner
                    || '"."'
                    || a.table_name
                    || '"' AS full_table_name,
                a.constraint_name,
                b.status
            FROM user_constraints a
            JOIN user_constraints b
                ON ( a.r_constraint_name = b.constraint_name
                    AND a.r_owner = b.owner )
            WHERE a.constraint_type = 'R'
                AND b.status = 'ENABLED'
            ORDER BY 1

FULL_TABLE_NAME
    CONSTRAINT_NAME STATUS
"XXX"."PURCHASES"   ITEMS_FK    ENABLED
"XXX"."PURCHASES"   CUSTOMERS_FK    ENABLED

select owner, table_name, r_constraint_name, status
 from user_constraints
where constraint_type = 'R';

OWNER   TABLE_NAME  R_CONSTRAINT_NAME   STATUS
XXX PURCHASES   CUSTOMERS_PK    DISABLED
XXX PURCHASES   ITEMS_PK    DISABLED