PostgreSQL – How to Get Current and Next Values of Sequence

ByAdmin

You can use Sequences to generate unique integer values, often used as auto-incrementing primary keys in tables. You can obtain the current value and the next value of a sequence using the currval and nextval functions, respectively. These functions are typically used within SQL statements or in PL/pgSQL code.

Current Value (currval): To get the current value of a sequence, you need to specify the name of the sequence as an argument to the currval function. Here’s the syntax:

SELECT currval('sequence_name');

Replace 'sequence_name' with the actual name of the sequence you want to check. Note that you should have already called nextval on the sequence in the current session before using currval to retrieve its current value.Example:

SELECT currval('my_sequence');

Next Value (nextval): To get the next value of a sequence and increment the sequence, you can use the nextval function. Here’s the syntax:

SELECT nextval('sequence_name');

Again, replace 'sequence_name' with the name of the sequence you want to retrieve the next value for.Example:

SELECT nextval('my_sequence');
  • You should use nextval to advance the sequence before using currval, as currval retrieves the last value generated by nextval within the current session.
  • If you attempt to use currval without having previously called nextval in the current session or if the sequence has not been used in the current session at all, it will result in an error.
  • Sequences are typically associated with specific columns in tables, so you would use these functions in the context of an INSERT statement to generate auto-incrementing primary key values.

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