######建立主表及子表

SQL> create table t_parent(a int primary key,b int);--采用内建约束方式

Table created.

SQL> create table t_child(a int primary key,parent int constraint fk_t_child references t_parent(a));##注意建立外键约束的语法

Table created.

SQL> select table_name,constraint_name,status from user_constraints;

TABLE_NAME                     CONSTRAINT_NAME                STATUS
------------------------------ ------------------------------ --------
T_CHILD                        FK_T_CHILD                     ENABLED ##子表的外键约束

T_PARENT                       SYS_C006006                    ENABLED ##主表的pk约束
T_CHILD                        SYS_C006007                    ENABLED ##子表的pk约束

SQL> select index_name,table_name from user_indexes;  ###查看创建约束相关索引的情况

INDEX_NAME                     TABLE_NAME
------------------------------ ------------------------------
SYS_C006007                    T_CHILD
SYS_C006006                    T_PARENT

SQL> drop table t_parent cascade constraints;###删除主表加上cascade constraints

Table dropped.

SQL> select index_name,table_name from user_indexes;###主表的pk约束对应的索引没有了

INDEX_NAME                     TABLE_NAME
------------------------------ ------------------------------
SYS_C006007                    T_CHILD

SQL> select table_name,constraint_name,status from user_constraints;###主子表的约束(pk)，但外键约束没有了

TABLE_NAME                     CONSTRAINT_NAME                STATUS
------------------------------ ------------------------------ --------
T_CHILD                        SYS_C006007                    ENABLED
BIN$i21D732Aid/gQAB/AQAJZA==$0 BIN$i21D731+id/gQAB/AQAJZA==$0 ENABLED

6 rows selected.

SQL>