--第一步：创建表，及相应的主键约束pk_test_id
SQL> create table test(id number constraint pk_test_id primary key);

Table created.
--第二步：此时总共有9个约束
SQL> select constraint_name from user_constraints;

CONSTRAINT_NAME
------------------------------
BIN$vL7ij8sVLTjgQAB/AQAPeg==$0
PK_TEST_ID
BIN$vL7ij8sYLTjgQAB/AQAPeg==$0
BIN$uvy0dxvyoYvgQAB/AQAMpQ==$0
BIN$uvy0dxwAoYvgQAB/AQAMpQ==$0
BIN$uvy0dxvsoYvgQAB/AQAMpQ==$0
BIN$uvy0dxvvoYvgQAB/AQAMpQ==$0
BIN$uvy0dxv6oYvgQAB/AQAMpQ==$0
BIN$uvy0dxv9oYvgQAB/AQAMpQ==$0

9 rows selected.
--第三步：删除表,按理说相应的约束应该被干掉了
SQL> drop table test;

Table dropped.
--第四步：此时还有9个约束，只是把约束的名称改了下，难道相应的约束没被干掉？
SQL> select constraint_name from user_constraints;

CONSTRAINT_NAME
------------------------------
BIN$vL7ij8sVLTjgQAB/AQAPeg==$0
BIN$vL7ij8sYLTjgQAB/AQAPeg==$0
BIN$vL7ij8sbLTjgQAB/AQAPeg==$0
BIN$uvy0dxvyoYvgQAB/AQAMpQ==$0
BIN$uvy0dxwAoYvgQAB/AQAMpQ==$0
BIN$uvy0dxvsoYvgQAB/AQAMpQ==$0
BIN$uvy0dxvvoYvgQAB/AQAMpQ==$0
BIN$uvy0dxv6oYvgQAB/AQAMpQ==$0
BIN$uvy0dxv9oYvgQAB/AQAMpQ==$0

9 rows selected.

SQL> create table test(id number constraint pk_test_id primary key);
 
Table created
SQL> select table_name from user_tables;
 
TABLE_NAME
------------------------------
TEST
SQL> select table_name,constraint_name from user_constraints;
 
TABLE_NAME                     CONSTRAINT_NAME
------------------------------ ------------------------------
TEST                           PK_TEST_ID
SQL> drop table test;
 
Table dropped
SQL> select table_name from user_tables;    --BIN$VnncqINTRy+7ruGTE76IlQ==$0为删除后的表名
 
TABLE_NAME
------------------------------
BIN$VnncqINTRy+7ruGTE76IlQ==$0    
SQL> select table_name,constraint_name from user_constraints;    --table_name跟user_table的表名相同，可以关联上
 
TABLE_NAME                     CONSTRAINT_NAME
------------------------------ ------------------------------
BIN$VnncqINTRy+7ruGTE76IlQ==$0 BIN$nIZCU2gMRrujmIOafsDtBg==$0
SQL> flashback recyclebin;   --清空回收站
 
Done
SQL> select table_name from user_tables;
 
TABLE_NAME
------------------------------
SQL> select table_name,constraint_name from user_constraints;
 
TABLE_NAME                     CONSTRAINT_NAME
------------------------------ ------------------------------