After reading my previous article about SEQUENCE one of my friend asked a question about the performance of using Sequence for quick and continuous generation and whether there is a way to create and manage this using Management Studio ?
Yes, SEQUENCE support CACHE option
Using CACHE option, you can specify how many values should be pre generated and available ready, you can set the cache size based on your application’ requirement.
Default cache size is 20
To use in Loop for quick processing
To get a range of numbers to use in a loop, you can use sp_sequence_get_range System stored procedure, so that you can get a range and not have to use NEXT VALUE option for each loop call
You can use [Sequence First Value] and [Sequence Last Value] and use it in your loop to insert data.
How to create and manage SEQUENCE from Management Studio ?
Step 1 : Open SQL Server “Denali” Management Studio, and connect to SQL Server “Denali” instance and go to your database in Object Explorer
Step 2: Expand “Programmability” and then expand "Sequences" to currently available ones
Step 3: To create a new sequence, right click on Sequence and click on “New Sequence”
Step 4: Specify the name and other required options such as Start Value, Increment By, etc.. and click “Ok” to create Sequence
Step 5: To modify the Sequence, right click on the selected sequence and click “Properties”
If you see the above screenshot, you might notice that Data Type, Precision or name of sequence can not be modified. You can change the other values, similarly you will see an option to restart the sequence as well.
Note: To rename you can use the “Rename” option in Context menu.
Step 6: To drop the sequence, right click on the selected sequence and click “Delete”
Let me know your experiences and feedback about SEQUENCEs
SQL Server “Denali” introduces a new feature called “SEQUENCE”. SEQUENCE is a user-defined object that generates a sequence of numeric values according to specified options.
Its not bound to a table like IDENTITY, You can use SEQUENCE across tables
Supported Data Types for creating SEQUENCE are as follows:
The above code creates a simple SEQUENCE with starting number as 1 and increments by 1
To get the next number in SEQUENCE, you need to use “NEXT VALUE” option
The below code might syntactically look same as the SEQUENCE "- RunningNumbers, but if you look at the output, its entirely different
If you see the output from RunningNumbers2, you will be getting a Negative value, its due to not specifying the Start number, so make sure you specify a Positive Start Number if you don’t want your table keys to Negative
Other options available in Creating Sequence are as follows:
You can specify Minimum Value and Maximum Value and whether to Cycle the numbers when reaching maximum value or not
If you see the below output, for every 5 records, the IDs are recycling and starts from 1 again
Restarting the Sequence
To restart the Sequence, you need to ALTER the sequence with RESTART option and start value
Since we restarted the Sequence with 1, Now we are getting output as 1 for RunningNumber2
Find the available Sequences in a database
You can Sys.Sequence system view to query the list of available Sequences in a database
How to use it as Identity across tables ?
Create tables for each reqion
Insert data to table using Sequences
Query the inserted data
If you see the Union output from 4 different tables, we are able to create a identity column across 4 tables, This will be very helpful when you horizontally partition data across tables
Delete the Sequences
I hope you all find this information about Sequences useful and informative !!!