In PostgreSQL, the “LASTVAL()” function is an inbuilt function that assists in working with sequences. It retrieves the most recently generated sequence value within the current session. This function is session-specific, meaning it only retrieves the last value of a sequence fetched within the current session. However, calling the LASTVAL() function before NEXTVAL() function in the current session will show you a “lastval of the sequence is not yet defined” error.

This write-up illustrates a complete process of fixing the “lastval of the sequence is not yet defined” error in PostgreSQL.

How to Fix the “lastval is not yet defined” Error When Calling/Invoking LASTVAL() in Postgres?

The stated error occurs when the LASTVAL() function is invoked before the NEXTVAL() function. For a profound understanding, let’s create a new sequence and apply the LASTVAL() function to it:

CREATE SEQUENCE commandprompt;

The below snippet shows that when the NEXTVAL() function is not used in the current session then directly invoking the LASTVAL() function will throw the stated error:

SELECT LASTVAL();

To rectify this error, all you need to do is invoke the NEXTVAL() function before the LASTVAL() function at least once:

SELECT NEXTVAL('commandprompt'),
NEXTVAL('commandprompt');

In this example, the NEXTVAL() function is invoked a couple of times:

Now call the LASTVAL() function to see how it works:

SELECT LASTVAL();

Note that the LASTVAL() function doesn’t accept any argument. The output snippet shows that the “LASTVAL()” function shows the last retrieved value of the NEXTVAL() function in the current session:

That’s all about fixing the “lastval of the sequence is not yet defined” error in PostgreSQL.

Conclusion

In PostgreSQL, the “lastval of the sequence is not yet defined” error occurs when the LASTVAL() function is invoked/called prior to the NEXTVAL() function. To fix the stated error, all you need to do is invoke the NEXTVAL() function before the LASTVAL() function at least once. This write-up has illustrated the complete process of fixing the “lastval of the sequence is not yet defined” error in PostgreSQL.