A Sequence is a database item that creates a unique integer sequence. These numbers are used as primary keys in tables or for other uses that need a unique identification. A sequence can be used to produce unique client IDs, order numbers, or invoice numbers, for example. Sequences can also be used for other reasons when a unique number is required, such as creating unique session IDs for online applications.
Sequences are a quick and easy technique to produce unique integers in a SQL database.
Why Sequences?
Generating unique identifiers
Sequences may be used to produce unique primary keys for tables, which are used to identify each row. Even if the table has millions of entries, this assures that each row has a unique identity.
Consistency
Sequences guarantee that each produced value is distinct and consistent.
This can be useful in a variety of applications, particularly those involving financial transactions or other sensitive data.
Flexibility
Sequences can have various starting values, increment values, and maximum or minimum values.
Sequence Syntax
CREATE SEQUENCE customer_id_seq START WITH 1 INCREMENT BY 1 MINVALUE 1 MAXVALUE 9999 CYCLE; INSERT INTO customers (customer_id, customer_name, customer_email) VALUES (NEXT VALUE FOR customer_id_seq, 'Raj Bhatt', 'rajbhatt993@gmail.com');
The CREATE SEQUENCE command in SQL is used to construct a Sequence, which defines the Sequence’s starting value, increment value, maximum value, and other parameters. Once constructed, a sequence may be used to generate unique integers with the NEXTVAL or CURRVAL functions.
The NEXTVAL method delivers the Sequence’s next available value, whereas the CURRVAL function returns the Sequence’s current value. Each time a value is created, the Sequence is automatically increased, ensuring that the next value supplied by NEXTVAL is always unique.
Sequences in SQL are commonly used to generate primary keys for tables.
How To drop a sequence in SQL
DROP SEQUENCE customer_id_seq;
How To check all Sequence available in Database
SELECT * FROM sys.sequences Order by name desc
Summary
- A sequence is a database item that creates a series of unique integers.
- Primary key values for tables are frequently generated using sequences.
- Sequences may be generated in Oracle using the “CREATE SEQUENCE” command or in Microsoft SQL Server using the “SEQUENCE” object.
- While generating a series, the initial value, increment, and other parameters can be given.
- To utilise a sequence to create values in a table, use the “NEXT VALUE FOR” syntax in SQL Server or the “SEQUENCE NAME.NEXTVAL” syntax in Oracle in an INSERT statement.
- In SQL, sequences can be discarded using the “DROP SEQUENCE” command.
Note
It is critical when utilising sequences to verify that the values created are unique and do not exceed any limits imposed on the table column.
