currval()
Synopsis
Use the currval( sequence_name ) function to return the last value returned by the nextval( sequence_name ) function for the specified sequence in the current session.
Semantics
sequence_name
Specify the name of the sequence.
- An error is raised if 
nextval( sequence_name )has not been called for the specified sequence in the current session. 
Examples
Create a sequence
yugabyte=# CREATE SEQUENCE s;
CREATE SEQUENCE
Call nextval().
yugabyte=# SELECT nextval('s');
 nextval
---------
       1
(1 row)
yugabyte=# SELECT currval('s');
 currval
---------
       1
(1 row)
Call currval() before nextval() is called.
yugabyte=# CREATE SEQUENCE s2;
CREATE SEQUENCE
SELECT currval('s2');
ERROR:  currval of sequence "s2" is not yet defined in this session