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.

Similar Posts

PostgreSQL – How to Rename a Sequence

ByAdmin

You can rename a sequence using the ALTER SEQUENCE statement with the RENAME TO clause in PostgreSQL database. Here’s the basic syntax for renaming a sequence: ALTER SEQUENCE old_sequence_name RENAME TO new_sequence_name; where old_sequence_name is the current name of the sequence you want to rename, and new_sequence_name is the new name you want to assign…

PostgreSQL – How to Check if User is Superuser

ByAdmin

The is_superuser configuration setting or attribute determines whether a user has superuser privileges or not. Superusers have the highest level of access and control over a PostgreSQL database cluster, including the ability to perform critical administrative functions. The is_superuser setting is a boolean attribute associated with database roles (users). When a user is designated as…

PostgreSQL – How to Change a User’s Password

ByAdmin

To change a user’s password in PostgreSQL, you can use the ALTER USER statement. Here’s how you can change a user’s password: Connect to PostgreSQL: You need to connect to your PostgreSQL server using a user account with superuser or administrative privileges, as only superusers can change the passwords of other users. Change the Password:To…

PostgreSQL – How to Rename a Column

ByAdmin

To rename a column in PostgreSQL, you can use the ALTER TABLE statement with the RENAME COLUMN clause. Below is the basic syntax for renaming a column in PostgreSQL: ALTER TABLE table_name RENAME COLUMN old_column_name TO new_column_name; where table_name is the name of the table containing the column you want to rename, old_column_name is the…

PostgreSQL – How to List All Databases

ByAdmin

To list all databases in PostgreSQL, you can use the following SQL command: SELECT datname FROM pg_database; Above query will display a list of database names currently available on the server. You should have the necessary permissions to list databases on the PostgreSQL server. If you encounter permission issues, make sure you are logged in…