Summary: in this tutorial, you will learn about the PostgreSQL SERIAL pseudo-type and how to use the SERIAL pseudo-type to define auto-increment columns in tables.

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Introduction to the PostgreSQL SERIAL pseudo-type

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In PostgreSQL, a sequence is a special kind of database object that generates a sequence of integers. A sequence is often used as the primary key column in a table.

When creating a new table, the sequence can be created through the SERIAL pseudo-type as follows:

By assigning the SERIAL pseudo-type to the id column, PostgreSQL performs the following:

• First, create a sequence object and set the next value generated by the sequence as the default value for the column.
• Second, add a NOT NULL constraint to the id column because a sequence always generates an integer, which is a non-null value.
• Third, assign the owner of the sequence to the id column; as a result, the sequence object is deleted when the id column or table is dropped

Behind the scenes, the following statement:

is equivalent to the following statements:

PostgreSQL provides three serial pseudo-types SMALLSERIAL, SERIAL, and BIGSERIAL with the following characteristics:

PostgreSQL SERIAL example

It is important to note that the SERIAL does not implicitly create an index on the column or make the column as the primary key column. However, this can be done easily by specifying the PRIMARY KEY constraint for the SERIAL column.

The following statement creates the fruits table with the id column as the SERIAL column:

To assign the default value for a serial column when you insert row into the table, you ignore the column name or use the DEFAULT keyword in the INSERT statement.

See the following example:

Or

PostgreSQL inserted two rows into the fruits table with the values for the id column are 1 and 2.

To get the sequence name of a SERIAL column in a table, you use the pg_get_serial_sequence() function as follows:

You can pass a sequence name to the currval() function to get the recent value generated by the sequence. For example, the following statement returns the recent value generated by the fruits_id_seq object:

If you want to get the value generated by the sequence when you insert a new row into the table, you use the RETURNING id clause in the INSERT statement.

The following statement inserts a new row into the fruits table and returns the value generated for the id column.

The sequence generator operation is not transaction-safe. It means that if two concurrent database connections attempt to get the next value from a sequence, each client will get a different value. If one client rolls back the transaction, the sequence number of that client will be unused, creating a gap in the sequence.

In this tutorial, you have learned how to use the PostgreSQL pseudo-type SERIAL to create an auto-increment column for a table.

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A quick reference to PostgreSQL.

Created on: 2019-01-22

Tag: cheat_sheet

To check postgresql version:

source: https://stackoverflow.com/a/13733856

To create a super suer with passowrd:

To create a database on Postgresql:

To remove an extension:

To connect to remote psql host 1:

To backup a psql database without typing password 2:

To create database from sql file:

to backup a single table:

to export a sql statement output to a csv file with header:

to export a sql statement output to a geojson file:

COPY current_relation_members TO '/var/lib/postgresql/csv/current_relation_members.CSV' DELIMITER ',' CSV HEADER;

The following are the Meta-Commands for psql command. This can be used with either with -c flag of the psql command like:

Or within the interactive prompt that comes after sudo -u postgres psql command. There are many Meta-Commands and there are available in the psql document. Bellow are a few useful most useful for me:

• connect to a database: c $DATEBASE_NAME

• list all users: du

• list all database: l or list

• list all table: dt

To allow remote connections to PostgreSQL database server, first check listen_addresses in postgresql.conf:

The output would show something like this:

Now let's edit the postgresql.conf file in our editor of choice:

Search for listen_addresses, and set it to '*' for all addresses or comma separated IP address, save the file and exit. Now we need to change the pg_hba.conf file so let's open it with our editor:

More details here PostgreSQL: Documentation: Connections and Authentication.

Now add the following to the end of file:

Now save the file and exit. Now restart PostgreSQL:

OR:

source: https://bosnadev.com/2015/12/15/allow-remote-connections-postgresql-database-server/

Now connect to the remote server:

source: https://askubuntu.com/a/423181

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