Oracle Auto-Increment Sequence Guide

Oracle can generate incrementing numbers by using Sequences. A Sequence is an object that can generate unique numerical values. You can create and use Sequences by following these steps:

Firstly, create a sequence in the Oracle database. You can use the CREATE SEQUENCE statement to create a sequence, as shown below:

   CREATE SEQUENCE sequence_name
   START WITH initial_value
   INCREMENT BY increment_value
   MINVALUE min_value
   MAXVALUE max_value
   NOCACHE;

sequence_name is the name of the sequence, initial_value is the starting value of the sequence, increment_value is the step by which the sequence increases, min_value is the smallest value of the sequence, max_value is the largest value of the sequence, and NOCACHE indicates not to cache the values of the sequence.

In tables where an auto-increment sequence is needed, use the NEXTVAL function of the sequence to obtain the next sequence value. The NEXTVAL function can be used in an INSERT statement as shown below:

   INSERT INTO table_name (column1, column2, column3, ...)
   VALUES (sequence_name.NEXTVAL, value1, value2, ...);

In this way, every time the INSERT statement is executed, the next value of the sequence will be inserted into the specified column of the table.

3. The CURRENT VALUE function of a sequence can be used to obtain the current value of the sequence. For example, you can use a SELECT statement to retrieve the current sequence value as shown below:

   SELECT sequence_name.CURRVAL
   FROM dual;

This will return the value of the current sequence.

It is important to note that a sequence is an object independent of a table and can be used in multiple tables to generate incrementing values.