CURRVAL FAQS

 1. What is CURRVAL in Oracle?

• CURRVAL is a function that returns the current value of a sequence in Oracle, i.e., the most recently generated value from the sequence using NEXTVAL in the current session.

2. Can I use CURRVAL without using NEXTVAL first?

• No, you must use NEXTVAL at least once in the current session before you can use CURRVAL. Attempting to use CURRVAL without calling NEXTVAL will result in an error.

3. Can CURRVAL be used across different sessions?

• No, CURRVAL is session-specific. It will only return the value generated by NEXTVAL in the same session where NEXTVAL was called. Other sessions cannot access the CURRVAL of a sequence from a different session.

4. What happens if I restart my session?

• If you restart your session, the sequence's current value will be reset. CURRVAL will reflect the most recent value generated from the NEXTVAL call in the new session.

5. What is the order of using NEXTVAL and CURRVAL?

• You must call NEXTVAL first to increment the sequence and generate a value. Then you can call CURRVAL to retrieve the value that was just generated. If you try to call CURRVAL before NEXTVAL, Oracle will throw an error.

6. Can I modify the sequence value using CURRVAL?

• No, CURRVAL is a read-only function. It simply returns the current value of the sequence, but it cannot be used to modify or reset the sequence.

7. Can CURRVAL be used in a SELECT query?

• Yes, CURRVAL can be used in a SELECT query after calling NEXTVAL. Example:

·        SELECT emp_seq.CURRVAL FROM dual;

8. What happens if I call NEXTVAL multiple times?

• Each time you call NEXTVAL, the sequence value will be incremented. CURRVAL will return the most recent value generated by the last NEXTVAL call.

9. Can CURRVAL be used in an INSERT statement?

• Yes, CURRVAL can be used in an INSERT statement if you need to reference the last generated sequence value after an insertion. Example:

·        INSERT INTO orders (order_id, customer_id)

·        VALUES (emp_seq.NEXTVAL, 101);

·         

·        INSERT INTO order_log (order_id, log_date)

·        VALUES (emp_seq.CURRVAL, SYSDATE);

10. What is the difference between CURRVAL and NEXTVAL?

• NEXTVAL: Generates the next value in the sequence and increments it.
• CURRVAL: Returns the current value of the sequence, i.e., the last value generated by NEXTVAL in the current session.

11. What happens if the sequence reaches its maximum value?

• If a sequence reaches its maximum value, and if the sequence is not set to cycle, attempting to call NEXTVAL will result in an error. If the sequence is set to cycle, it will restart from the minimum value.

12. Can I use CURRVAL with any sequence?

• Yes, you can use CURRVAL with any sequence in Oracle, as long as you have first called NEXTVAL in the same session.

13. What if I need to generate a descending sequence?

• You can specify a negative increment when creating a sequence to generate a descending sequence. For example:

·        CREATE SEQUENCE emp_seq

·        START WITH -1

·        INCREMENT BY -1;

14. Can I drop a sequence while using CURRVAL?

• Yes, you can drop a sequence using DROP SEQUENCE. However, you cannot use CURRVAL after the sequence is dropped, as the sequence will no longer exist.

15. How can I avoid errors when using CURRVAL?

• Always ensure that NEXTVAL is called before CURRVAL in the same session. Be mindful of session boundaries and avoid calling CURRVAL in different sessions, as it is specific to the session where NEXTVAL was invoked.