I am little bit confused about my query. I am getting error but it works.
I am using ORACLE 11gR2 in command prompt.
I have created 2 tables dp (department) and em (employee) with Primary key and foreign key.
If I run the script couple of times, the DROP TABLE function attempts to drop the table 2 times but it should try only once. Could you please give me any idea of why it is happening. My script is given below.

```
cl scr

DROP TABLE dp CASCADE CONSTRAINT ;
L
// DROP TABLE dp PURGE ;
L
CREATE TABLE dp (
    dpid    NUMBER(2),
    dname   VARCHAR2(20));

DROP TABLE em PURGE ;
CREATE TABLE em (
    emid    NUMBER(2),
    ename   VARCHAR2(20),
    dpid    NUMBER(2));

ALTER TABLE dp
ADD CONSTRAINT pk_dp_dpid PRIMARY KEY (dpid) ;

ALTER TABLE em
ADD CONSTRAINT fk_em_dp_dpid FOREIGN KEY (dpid)
REFERENCES dp (dpid) ;

```