title: SQL doesn't allow me to insert data
body: <p>creating table and inserting data into a table and now it giving me an error </p>
  
  <blockquote>
    <p>SQL Error: ORA-02291: integrity constraint (S21403051.SYS_C007300)
    violated - parent key not found         02291. 00000 - "integrity
    constraint (%s.%s) violated - parent key not found"         *Cause:</p>
  </blockquote>
  
  <pre><code>CREATE TABLE CUSTOMER(
   CUSTOMER_ID VARCHAR(10) PRIMARY KEY,
   FIRST_NAME  VARCHAR(10),
   SURNAME VARCHAR(15),
   CUSTOMER_TEL VARCHAR(12),
  CUSTOMER_EMAIL VARCHAR(30)
  )
  
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_1', 'CUST_102', 'EMP_51');
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_3','CUST_101','EMP_51');
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_3','CUST_101','EMP_53');
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_5','CUST_103','EMP_54');
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_5','CUST_107','EMP_54');
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_1', 'CUST_106','EMP_55');
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_1','CUST_108','EMP_55');
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_5','CUST_104','EMP_51');
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_3','CUST_109','EMP_51');
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_2','CUST_1010','EMP_52');
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_2','CUST_1010','EMP_55');
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_5','CUST_101','EMP_51');
  INSERT INTO CUSTOMER_CRUISES VALUES ( 'CRUISE_5','CUST_103','EMP_51');
  </code></pre>