![]() ![]() If sequence values in a table are required to be unique throughout a group of tables, create triggers to prevent duplicates caused by update statements or sequence number cycling. ![]() If sequence values in a table are required to be unique, create a unique constraint on the column. The ability to reuse sequence values is by design. Uniqueness is not automatically enforced for sequence values. To prevent sequence values from being changed, use an update trigger on the table to roll back changes. Unlike identity columns, whose values cannot be changed, sequence values are not automatically protected after insertion into the table. You need to change the specification of the sequence, such as the increment value. Calling sp_sequence_get_range can retrieve several numbers in the sequence at once. Requesting identity values could result in gaps in the series if other processes were simultaneously issued numbers. ![]() For example, an application needs to reserve five sequential numbers. The OVER clause guarantees that the values returned are generated in the order of the OVER clause's ORDER BY clause.Īn application requires multiple numbers to be assigned at the same time. The NEXT VALUE FOR function can apply the OVER clause to the function call. The application requires sequence values to be sorted by another field. For example, after assigning values 1 through 10, the application starts assigning values 1 through 10 again. The application must restart the number series when a specified number is reached. ![]() The application requires sharing a single series of numbers between multiple tables or multiple columns within a table. The application requires a number before the insert into the table is made. Use sequences instead of identity columns in the following scenarios: If the data type is not specified, a sequence defaults to bigint. Use sp_sequence_get_range to get a range of multiple sequence numbers at once.Ī sequence can be defined as any integer data type. The NEXT VALUE FOR function can be used as the default value for a column in a table definition. The sequence number is allocated when NEXT VALUE FOR is called even if the number is never inserted into a table. Unlike identity column values, which are generated when rows are inserted, an application can obtain the next sequence number before inserting the row by calling the NEXT VALUE FOR function. For information about the options, see CREATE SEQUENCE. Options enable you to control the increment, maximum and minimum values, starting point, automatic restarting capability, and caching to improve performance. User applications can reference a sequence object and coordinate the values keys across multiple rows and tables.Ī sequence is created independently of the tables by using the CREATE SEQUENCE statement. The relationship between sequences and tables is controlled by the application. An application refers to a sequence object to receive its next value. Sequences, unlike identity columns, are not associated with tables. The sequence of numeric values is generated in an ascending or descending order at a defined interval and may cycle (repeat) as requested. Applies to: SQL Server Azure SQL Database Azure SQL Managed InstanceĪ sequence is a user-defined schema-bound object that generates a sequence of numeric values according to the specification with which the sequence was created. ![]()
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