Explanation:
: the EMP_ID_SEQ sequence is not affected by modification to the EMPLOYEES table. Any other column of NUMBER data type in your schema can use the EMP_ID_SEQ sequence. Incorrect answer :
1: EMP_ID_SEQ sequence can be use to populate JOB_ID
2: EMP_ID_SEQ sequence will not be invalidate when column in EMPLOYEE_ID is modify.
5: EMP_ID_SEQ sequence will be dropped automatically when you drop the EMPLOYEES table.
6: EMP_ID_SEQ sequence will be dropped automatically when you drop the EMPLOYEE_ID column.
Reference:
Introduction to Oracle9i : SQL, Oracle University Study Guide, 12-4

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