Examine the structure of the EMPLOYEES table:
EMPLOYEE_ID NUMBER NOT NULL, Primary Key
EMP_NAME VARCHAR2(30)
JOB_ID NUMBER\\
SAL NUMBER
MGR_ID NUMBER . References EMPLOYEE_ID column
DEPARTMENT_ID NUMBER . Foreign key to DEPARTMENT_ID column of the. . DEPARTMENTS table
You created a sequence called EMP_ID_SEQ in order to populate sequential values for the EMPLOYEE_ID
column of the EMPLOYEES table.Which two statements regarding the EMP_ID_SEQ sequence are true? (Choose two.)
A.
You cannot use the EMP_ID_SEQ sequence to populate the JOB_ID column.
B.
The EMP_ID_SEQ sequence is invalidated when you modify the EMPLOYEE_ID column.
C.
The EMP_ID_SEQ sequence is not affected by modifications to the EMPLOYEES table.
D.
Any other column of NUMBER data type in your schema can use the EMP_ID_SEQ sequence.
E.
The EMP_ID_SEQ sequence is dropped automatically when you drop the EMPLOYEES table.
F.
The EMP_ID_SEQ sequence is dropped automatically when you drop the EMPLOYEE_ID column.
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:
A:
EMP_ID_SEQ sequence can be use to populate JOB_ID
B:
EMP_ID_SEQ sequence will not be invalidate when column in EMPLOYEE_ID is modify.
E:
EMP_ID_SEQ sequence will be dropped automatically when you drop the EMPLOYEES table.
F:
EMP_ID_SEQ sequence will be dropped automatically when you drop the EMPLOYEE_ID column.
Refer: Introduction to Oracle9i: SQL, Oracle University Study Guide, 12-4
Sequence numbers are generated independently of tables, so the same sequence can be used for one or for multiple tables.
https://docs.oracle.com/cd/B28359_01/server.111/b28286/statements_6015.htm#SQLRF01314
Caution:
Before dropping a table, familiarize yourself with the consequences of doing so:
Dropping a table removes the table definition from the data dictionary. All rows of the table are no longer accessible.
All indexes and triggers associated with a table are dropped.
All views and PL/SQL program units dependent on a dropped table remain, yet become invalid (not usable). See “Managing Object Dependencies” for information about how the database manages dependencies.
All synonyms for a dropped table remain, but return an error when used.
All extents allocated for a table that is dropped are returned to the free space of the tablespace and can be used by any other object requiring new extents or new objects. All rows corresponding to a clustered table are deleted from the blocks of the cluster. Clustered tables are the subject of Chapter 20, “Managing Clusters”.
So won’t drop sequence if it’s independent from one table. Many other tables could be using it