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Sequences and Increments

Sequences are user defined ordered list of integers. You can define a sequence like 1,2,3,4,5 or multiple of something like 2,4,6,8,10 among different combinations. Since these are unique, typically they are used as primary keys.

Creating a Sequence

We can create a new sequence using the CREATE SEQUENCE statement. For example:

CREATE SEQUENCE increment_by_two INCREMENT 2 START 2;

Now the above statement creates a sequence called increment_by_two which starts at the value 2 and increments by 2.

Auto increment in PostgreSQL

Let's apply a simple sequence like 1,2,3,4,5... to a column.

CREATE TABLE profile( id SERIAL );

Here the id column has been assigned a data type called SERIAL which generates a sequence called profile_id_seq with values starting from 1 and followed by increments of 1. Typically id is used as a primary key and sequencing ensures the uniqueness of the column values.

Operating on Sequence

Once a sequence is created, it can be operated on using certain functions. Primarily to fetch the current value, the next value in the sequence or (re)set the sequence to start from a new value.

  • nextval
  • currval
  • setval

The above functions can be used to perform the operations on the sequence.

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