What is the purpose of a sequence in SQL?

A sequence in SQL is used to generate a sequence of numeric values in a specific order.

In more detail, a sequence in SQL is a database object that is essentially a list of integers. It is used to automatically generate unique identifiers for rows of a table. This is particularly useful when you need to create a unique primary key value for new rows in a database table.

Sequences are created with the CREATE SEQUENCE statement, and the next value in the sequence can be obtained with the NEXT VALUE FOR function. The sequence of numbers generated by a sequence is not affected by rollbacks, and the sequence does not automatically reset when the maximum value for the sequence is reached.

The sequence object generates numbers according to the specifications defined during its creation, such as the starting point, the increment value, the maximum and minimum values, and whether the sequence should cycle when the limit is reached.

For example, if you have a table of students and you want to assign each student a unique ID, you could use a sequence. When a new student is added to the table, the sequence would automatically generate a new, unique ID for that student. This ensures that each student can be uniquely identified by their ID, which is particularly useful in large databases where manually assigning unique IDs would be impractical.

In summary, a sequence in SQL is a powerful tool for automatically generating unique identifiers, ensuring data integrity and simplifying database management.