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Sequence – Long awaited feature

As per BOL (https://msdn.microsoft.com/en-us/library/ff878058(v=sql.110).aspx) : A 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. The sequence of numeric values is generated in an ascending or descending order at a defined interval and may cycle (repeat) as requested. Sequences, unlike identity columns, are not associated with tables. An application refers to a sequence object to receive its next value. The relationship between sequences and tables is controlled by the application. User applications can reference a sequence object and coordinate the values keys across multiple rows and tables.

This feature is really a good to have and this feature is same as Oracle’s sequence objects.  A sequence object generates sequence of unique numeric values as per specifications mentioned.

A sequence can be defined as any integer data type. If the data type is not specified, a sequence defaults to bigint. A sequence value is not effected by SQL server restart. Many people think sequence is similar to identity. But big difference is sequence object is independent of a table while identity columns are attached to a table.

Create Sequence

CREATE SEQUENCE TEMPSEQ AS INT

START WITH 1 — START WITH VALUE 1

INCREMENT BY 1– INCREMENT WITH VALUE 1

MINVALUE 0 — MINIMUM VALUE TO START IS 0

MAXVALUE 5 — MAXIMUM IT CAN GO TO 5

NO CYCLE — DO NOT GO ABOVE 5

CACHE 2 — INCREMENT 2 VALUES IN MEMORY RATHER THAN INCREMENTING FROM IO

Generate value from Sequence

SELECT NEXT VALUE FOR TEMPSEQ AS seq_no;

Error when Sequence reach to MAX value

Msg 11728, Level 16, State 1, Line 18

The sequence object ‘TEMPSEQ’ has reached its minimum or maximum value. Restart the sequence object to allow new values to be generated.

Alter Sequence to RESTART it from 1 or desired value

ALTER SEQUENCE TEMPSEQ RESTART WITH 1

 

Create Sequence with CYCLE mode, where value will be reset to MIN value when it reaches to MAX value

CREATE SEQUENCE TEMPSEQ_CYCLE AS INT

START WITH 1 — START WITH VALUE 1

INCREMENT BY 1– INCREMENT WITH VALUE 1

MINVALUE 0 — MINIMUM VALUE TO START IS 0

MAXVALUE 5 — MAXIMUM IT CAN GO TO 5

CYCLE — RESET to 0 once reached to MAX VALUE 5

CACHE 2 — INCREMENT 2 VALUES IN MEMORY RATHER THAN INCREMENTING FROM IO

Output of Sequence with CYCLE

SELECT NEXT VALUE FOR TEMPSEQ_CYCLE AS ID, NAME FROM SYS.OBJECTS

Sequence

Alter existing Sequence to set it to CYCLE mode

ALTER SEQUENCE TEMPSEQ CYCLE — RESET to 0 once reached to MAX VALUE 5

Use Sequence in Table as Default constraint.

Scenario: We need to generate token for each customer coming to meet him with HR & finance personal.

  1. Create Sequence

CREATE SEQUENCE TOKENNO AS INT

START WITH 1 — START WITH VALUE 1

INCREMENT BY 1– INCREMENT WITH VALUE 1

MINVALUE 0 — MINIMUM VALUE TO START IS 0

MAXVALUE 5000 — MAXIMUM IT CAN GO TO 5000

NO CYCLE — RESET to 0 once reached to MAX VALUE 5000

CACHE 200 — INCREMENT 200 VALUES IN MEMORY RATHER THAN INCREMENTING FROM IO

  1. Create Table with Sequence

CREATE TABLE HR_EXECUTIVE_MEETING

(TOKENNO INT DEFAULT (NEXT VALUE FOR TOKENNO), DESKNO INT)

 

CREATE TABLE FINANCE_EXECUTIVE_MEETING

(TOKENNO INT DEFAULT (NEXT VALUE FOR TOKENNO), DESKNO INT)

  1. Insert into table having Sequence

INSERT INTO HR_EXECUTIVE_MEETING(TOKENNO,DESKNO) VALUES(DEFAULT,22)

INSERT INTO FINANCE_EXECUTIVE_MEETING(TOKENNO,DESKNO) VALUES(DEFAULT,7)

  1. Check the table values

SELECT * FROM HR_EXECUTIVE_MEETING

SELECT * FROM FINANCE_EXECUTIVE_MEETING

Sequence

Reference: Rohit Garg (http://mssqlfun.com/)

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Creation & Deletion of Database Snapshot by SQL Agent Job

Some days back, I received one query on my facebook page that user want to create Database Snapshot frequently & want to delete the oldest with same frequency. Quite interesting scenario. I did not go in deep why he has such requirement but I am clear that It can be done very easily.

So let’s do it. I have setup 2 scripts one for creation of snapshot & another is for deletion of snapshot. We can schedule a SQL agent jobs with 2 steps using these scripts.

Step 1 :-

DECLARE @CREATE_SS VARCHAR(MAX)

DECLARE @DT VARCHAR(100)

SET @DT = REPLACE(REPLACE(REPLACE(CONVERT(VARCHAR,GETDATE(),120),’-‘,’_’),’ ‘,’_’),’:’,’_’)

SET @CREATE_SS =

‘CREATE DATABASE TEST_’+@DT+’ ON

( NAME = TEST, FILENAME =

”C:\TEST_’+@DT+’.SS” )

AS SNAPSHOT OF TEST’

EXEC (@CREATE_SS)

Step 2 :-

IF(SELECT COUNT(*) FROM SYS.DATABASES WHERE SOURCE_DATABASE_ID = DB_ID(‘TEST’))>1

BEGIN

DECLARE @DROP_SS VARCHAR(MAX)

DECLARE @SS_NAME VARCHAR(100)

SELECT TOP 1 @SS_NAME = NAME FROM SYS.DATABASES WHERE SOURCE_DATABASE_ID = DB_ID(‘TEST’)

ORDER BY CREATE_DATE ASC

SET @DROP_SS = ‘DROP DATABASE ‘+ @SS_NAME

EXEC (@DROP_SS)

END

Reference : Rohit Garg (http://mssqlfun.com/)

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Thanks to Toadworld.com team for recognition !

Thanks to Toadworld.com team for recognition !

Toadworld.com Profile : http://www.toadworld.com/members/rohit-garg/blogs/default.aspx

If you liked this post, do like on Facebook at http://www.facebook.com/mssqlfun

Reference : Rohit Garg (http://mssqlfun.com/)

2013 with You & SQL Server

The WordPress.com stats helper monkeys prepared a 2013 annual report for this blog.

Here’s an excerpt:

The concert hall at the Sydney Opera House holds 2,700 people. This blog was viewed about 41,000 times in 2013. If it were a concert at Sydney Opera House, it would take about 15 sold-out performances for that many people to see it.

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Refresh Intellisense in SSMS(SQL Server Management Studio) 2008 & above

Intellisense is a new feature that comes with SSMS(SQL Server Management Studio) 2008 onwards. Intellisense makes coding quite easy.

But Sometimes I find that intellisense becomes stale and you start getting the wavy red lines when writing code. Even though object exists in database but Intellisense is not able to recognize it.

Refreshing the cache is quite easy but not necessarily strictly required.

Go to Edit -> IntelliSense -> Refresh Local Cache OR you can use shortcut Ctrl + Shift + R

You can check in below image that database has 5 table but intellisense showing only 4 tables. Table “JKL” is missing from intellisense list. You can refresh the Intellisense to get all tables.

More details on Intellisense can be found over MSDN : http://msdn.microsoft.com/en-us/library/hh245114.aspx

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Reference : Rohit Garg (http://mssqlfun.com/)

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