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SQL Server 2019 Hosting - HostForLIFE.eu :: Creating a custom sequence in MS-SQL Server

clock December 13, 2019 11:56 by author Peter

A sequence object in MS-SQL Server is designated to define and get only integer values, such as int, bigint, smallint, tinyint. However, if we want to generate sequence value(s) that are alpha-numeric, then we can define a Stored Procedure that can combine to generate an alpha-numeric combination of sequence values. This blog gives a complete idea of how this can be implemented.

CREATE DATABASE sampdb1

use sampdb1

--First Create a sequence object s3 which will generate numbers from 1 to 5 and cycles

CREATE SEQUENCE s3

START WITH 1

INCREMENT BY 1

MINVALUE 1

MAXVALUE 5

CYCLE

--Ensuring that the sequence object is defined properly and generating defined values.

SELECT NEXT VALUE FOR s3

--Defining a Stored Procedure that generates a Custom-sequence of values. This stored procedure is going to just get the generated alpha-numeric combination of the sequence.

CREATE PROCEDURE genSeqVals AS

Begin

DECLARE @n as int, @msg varchar(4)

SELECT @n=NEXT VALUE FOR s3

PRINT 'A'+cast(@n as varchar(2))

End

--Execute the following code and check.

Exec genSeqVals

--Defining another Stored Procedure that generates a Custom-sequence of values. This stored procedure returns the alpha-numeric combination of the sequence value that is generated using an OUTPUT parameter.

CREATE PROCEDURE getSeqVals(@res varchar(4) OUTPUT) AS

Begin

DECLARE @n as int, @msg varchar(4)

SELECT @n=NEXT VALUE FOR s3

SET @res = 'A'+cast(@n as varchar(2))

End

--Execute the following code and check.

DECLARE @seqnum varchar(4)

EXECUTE getSeqVals @seqnum output

print @seqnum


This is one way in which sequence objects can be custom-implemented as per the requirement. I hope that the above lines of code have given you deeper insight into T-SQL for custom implementation. Happy coding!

 



SQL Server 2019 Hosting - HostForLIFE.eu :: Drop Indexes In Views In SQL Server

clock December 3, 2019 11:51 by author Peter

In this article, I am going to tell about the dropping of indexes in View in SQL Server. Views are virtual tables in which data from one or more tables gives the result set as our SQL table does with rows and columns. A View doesn’t store the data permanently in the database and at the time of execution, only its result set gets determined. When a View contains a large amount of rows and has complex logic in it then we can create an index on a View to improve the query performance. A View consists of a Unique Clustered Index and it is stored in the database as the clustered index does. Now, let’s run a few scenarios to check when Clustered index which is created on a View gets dropped automatically.

First, I will create a table on which I will run those scenarios.
CREATE TABLE[dbo]. [Customer] 
    ( 
        [CustomerID][int] IDENTITY(1, 1) NOT NULL, [CustomerName][varchar](50) NOT NULL, [CEO][varchar](40) NULL, [Phone][varchar](20) NOT NULL PRIMARY KEY CLUSTERED( 
            [CustomerID] ASC)) 
GO 


Now, I will create a View which will use this Customer table.
-- Create view 
Create VIEW vw_customer 
 WITH SCHEMABINDING  
AS  
 SELECT  CustomerID, CustomerName, CEO 
  from dbo.Customer 
  GO 


Here in the definition of View, I have used WITH SCHEMABINDING which is necessary for creating an index on a View. This option simulates that we cannot delete any of the base table used in the View and in order to make any changes, first, we need to drop or alter the View.

Also, all the table references in a View should have two part naming convention (schemaname.tablename) as we have in vw_Customer view (dbo.Customer).

Now, I will create an index on our View.


Scenario 1

Create index IX_CustomerID  
 ON vw_customer (CustomerID); 
 GO 


Error returned: Cannot create index on view 'vw_customer'. It does not have a unique clustered index. On Views, the first index must be a unique clustered index, so this will throw the error.


So, the first index on View should be UNIQUE CLUSTERD INDEX, else it will throw an error.

Scenario 2
Create unique clustered index IX_CustomerID  
 ON vw_customer (CustomerID) 
 GO 

Now, our Indexed View is created having a clustered index on it. Now, I want to alter my View and add one more column GETDATE() as CurrentDate  in the View definition and alter the View.

Now, alter the View after Scenario 2.

Scenario 3
ALTER  VIEW vw_customer 
 WITH SCHEMABINDING  
AS  
 SELECT  CustomerID, CustomerName , GETDATE() as CurrentDate 
  from dbo.Customer 
GO 

Now, as I have altered the View, I want to create another index on column CustomerName which will be a NonClustered index.

Scenario 4
Create index IX_CustomerName  
 ON vw_customer (CustomerName); 
GO 


Again, I get an error: Cannot create index on view 'vw_customer'. It does not have a unique clustered index.

As we have already created Unique Clustered Index on View, still it gives an error. The interesting thing is that after updating the View, the index that was created in Scenario 2 is dropped and the code will throw the same error as in Scenario 1.

As mentioned here,
"ALTER VIEW can be applied to indexed views; however, ALTER VIEW unconditionally drops all indexes on the view."
Hope you will like this post.

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SQL Server 2019 Hosting - HostForLIFE.eu :: SQL Constraints Explained

clock November 12, 2019 10:22 by author Peter

In this blog, I will explain SQL Constraints. They are used to specify rules for the data in a table. The following SQL Constraints are commonly used (Primary key, foreign key, unique key, Composite key, null, Not Null, check).

Primary Key

The Primary key must contain be a unique value. It is the primary column and can’t have the null value. It uniquely identifies each row in a database table.
 
Syntax
    CREATE TABLE TB_NAME(Column1 datatype,column2 datatype PRIMARY KEY(Column1)) 

Foreign Key
1. Foreign key always refers to the primary key column.
2. Foreign key accepted to duplicate value.
 
Syntax
    CREATE TABLE TB_NAME(column1 datatype FOREIGN KEY REFERENCES(primary_key column_name),cloumn2 datatype) 

Unique Key
 
The unique key is the same as the primary key, but one row is accepted for the null value.
 
Syntax
    CREATE TABLE TB_NAME(Column_name datatatype UNIQUE,column_name2 datatype) 

Composite key
A composite key is a set of multiple keys that, together, uniquely identifies each record
 
Syntax
    CREATE TABLE TB_NAME(Column1 datatype,column2 datatype PRIMARY KEY(Column1,column2)) 

Not Null
Forces a column not to accept NULL values
 
Syntax
    CREATE TABLE TB_NAME(Column1 datatype,column2 datatype NOT NULL) 

Check
The CHECK constraint is used to limit the value range that can be placed in a column.
 
Syntax
    CREATE TABLE TB_NAME(MARKS INT CHECK(MARKS<=100))



SQL Server 2019 Hosting - HostForLIFE.eu :: How To Track Database Changes in SQL server?

clock November 6, 2019 11:33 by author Peter

Version control helps you to track the changes of a code repository. But, it doesn't much help to track database changes. General practice is to create a single script file that includes all the schema and update that file every time you make any changes into the database and commit it to version control. However, this is a bit longer a way to track the changes. Another way is to use popular tools like Red Gate Change Automation. But there is a native way around to handle tracking! simply put, DDL trigger can be used to track the DB changes.

Track Stored Procedure changes using DDL trigger

Here we'll see how to track stored procedure changes using DDL trigger.

Create your audit database and create a table.  
USE AuditDB;  
GO  
 
CREATE TABLE dbo.ProcedureChanges  
(  
    EventDate    DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,  
    EventType    NVARCHAR(100),  
    EventDDL     NVARCHAR(MAX),  
    DatabaseName NVARCHAR(255),  
    SchemaName   NVARCHAR(255),  
    ObjectName   NVARCHAR(255),  
    HostName     NVARCHAR(255),  
    IPAddress    VARCHAR(32),  
    ProgramName  NVARCHAR(255),  
    LoginName    NVARCHAR(255)  
);   

Add data of all existing stored procedures from your actual database (Product DB in this example)
USE ProductDB;  
GO  
 
INSERT AuditDB.dbo.ProcedureChanges  
(  
    EventType,  
    EventDDL,  
    DatabaseName,  
    SchemaName,  
    ObjectName  
)  
SELECT  
    N'Initial control',  
    OBJECT_DEFINITION([object_id]),  
    DB_NAME(),  
    OBJECT_SCHEMA_NAME([object_id]),  
    OBJECT_NAME([object_id])  
FROM  
    sys.procedures;  
Create DDL trigger to capture changes
USE ProductDB;  
GO  
 
CREATE TRIGGER CaptureStoredProcedureChanges  
    ON DATABASE  
    FOR CREATE_PROCEDURE, ALTER_PROCEDURE, DROP_PROCEDURE,   
    ALTER_SCHEMA, RENAME  
AS  
BEGIN  
    SET NOCOUNT ON;  
 
    DECLARE @EventData XML = EVENTDATA(), @ip VARCHAR(32);  
 
    SELECT @ip = client_net_address  
        FROM sys.dm_exec_connections  
        WHERE session_id = @@SPID;  
 
    INSERT AuditDB.dbo.ProcedureChanges  
    (  
        EventType,  
        EventDDL,  
        SchemaName,  
        ObjectName,  
        DatabaseName,  
        HostName,  
        IPAddress,  
        ProgramName,  
        LoginName  
    )  
    SELECT  
        @EventData.value('(/EVENT_INSTANCE/EventType)[1]',   'NVARCHAR(100)'),   
        @EventData.value('(/EVENT_INSTANCE/TSQLCommand)[1]', 'NVARCHAR(MAX)'),  
        @EventData.value('(/EVENT_INSTANCE/SchemaName)[1]',  'NVARCHAR(255)'),   
        @EventData.value('(/EVENT_INSTANCE/ObjectName)[1]',  'NVARCHAR(255)'),  
        DB_NAME(), HOST_NAME(), @ip, PROGRAM_NAME(), SUSER_SNAME();  
END  
GO  

Modify any stored procedure and check the ProcedureChanges table from AuditDB.

The method might have some limitations, but this is the simplest way to tracking changes of small size databases.



SQL Server 2019 Hosting - HostForLIFE.eu :: How To Track Database Changes in SQL server?

clock October 23, 2019 12:18 by author Peter

Version control helps you to track the changes of a code repository. But, it doesn't much help to track database changes. General practice is to create a single script file that includes all the schema and update that file every time you make any changes into the database and commit it to version control.

However, this is a bit longer a way to track the changes. Another way is to use popular tools like Red Gate Change Automation. But there is a native way around to handle tracking! simply put, DDL trigger can be used to track the DB changes.

Track Stored Procedure changes using DDL trigger

Here we'll see how to track stored procedure changes using DDL trigger.

Create your audit database and create a table. 
USE AuditDB; 
GO 
 
CREATE TABLE dbo.ProcedureChanges 

    EventDate    DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP, 
    EventType    NVARCHAR(100), 
    EventDDL     NVARCHAR(MAX), 
    DatabaseName NVARCHAR(255), 
    SchemaName   NVARCHAR(255), 
    ObjectName   NVARCHAR(255), 
    HostName     NVARCHAR(255), 
    IPAddress    VARCHAR(32), 
    ProgramName  NVARCHAR(255), 
    LoginName    NVARCHAR(255) 
);  
Add data of all existing stored procedures from your actual database (Product DB in this example)
USE ProductDB; 
GO 

 
INSERT AuditDB.dbo.ProcedureChanges 

    EventType, 
    EventDDL, 
    DatabaseName, 
    SchemaName, 
    ObjectName 

SELECT 
    N'Initial control', 
    OBJECT_DEFINITION([object_id]), 
    DB_NAME(), 
    OBJECT_SCHEMA_NAME([object_id]), 
    OBJECT_NAME([object_id]) 
FROM 
    sys.procedures; 
Create DDL trigger to capture changes
USE ProductDB; 
GO 
 
CREATE TRIGGER CaptureStoredProcedureChanges 
    ON DATABASE 
    FOR CREATE_PROCEDURE, ALTER_PROCEDURE, DROP_PROCEDURE,  
    ALTER_SCHEMA, RENAME 
AS 
BEGIN 
    SET NOCOUNT ON; 
 
    DECLARE @EventData XML = EVENTDATA(), @ip VARCHAR(32); 
 
    SELECT @ip = client_net_address 
        FROM sys.dm_exec_connections 
        WHERE session_id = @@SPID; 
 
    INSERT AuditDB.dbo.ProcedureChanges 
    ( 
        EventType, 
        EventDDL, 
        SchemaName, 
        ObjectName, 
        DatabaseName, 
        HostName, 
        IPAddress, 
        ProgramName, 
        LoginName 
    ) 
    SELECT 
        @EventData.value('(/EVENT_INSTANCE/EventType)[1]',   'NVARCHAR(100)'),  
        @EventData.value('(/EVENT_INSTANCE/TSQLCommand)[1]', 'NVARCHAR(MAX)'), 
        @EventData.value('(/EVENT_INSTANCE/SchemaName)[1]',  'NVARCHAR(255)'),  
        @EventData.value('(/EVENT_INSTANCE/ObjectName)[1]',  'NVARCHAR(255)'), 
        DB_NAME(), HOST_NAME(), @ip, PROGRAM_NAME(), SUSER_SNAME(); 
END 
GO  

Modify any stored procedure and check the ProcedureChanges table from AuditDB.

The method might have some limitations, but this is the simplest way to tracking changes of small size databases.



SQL Server 2019 Hosting - HostForLIFE.eu :: Enforcing Foreign Key Constraint In A Multi-Valued Column In SQL Server

clock October 4, 2019 09:04 by author Peter

I have seen that sometimes, a few developers create a multi-valued column to store more than one value in a comma-separated manner (like 1,3,4) and then, they read the individual values by splitting using comma.

However, due to such design, they can't add a foreign key constraint like below.

  • ALTER TABLE <Table-name> 
  • ADD CONSTRAINT <FK-Name> FOREIGN KEY (<col-name>) REFERENCES <Lookup Table-name>(<Lookup col-name>); 

PS - Personally, I am not a fan of such design and I would recommend having a mapping table in such cases; however, at times, mostly on the existing system, you don't have the choice to rewrite or change the design and hence finding a quick fix is the only option.
 
To illustrate the problem and solution, let's take an example of two tables - Employee and Country - as below.
    CREATE TABLE Country ( 
       Id INT NOT NULL PRIMARY KEY, 
       Name varchar(100) NOT NULL, 
       Code varchar(50) NULL 
    ); 
      
    CREATE TABLE Employee ( 
       Id INT NOT NULL PRIMARY KEY, 
       HomeCountryId INT NOT NULL, 
       VisitedCountryIds varchar(200) NULL, 
       Constraint FK_Employee_Country FOREIGN KEY (HomeCountryId) REFERENCES Country(Id) 
    ); 


Let's assume the country id as 1, 2 till 249 (As per the latest data available during the time of writing the post).
 
As you can see there is FK constraint on the HomeCountryId, hence only valid Country Id (from 1-249) can be entered; however, in the field VisitedCountryIds, there is no check and any id (like 250, 251, etc.) can also be added even if it doesn't exist in the country table. Well, this can lead to the data integrity issue.
 
So how we can make sure that users can only enter valid country ids (from 1-249) in the VisitedCountryIds column?
 
The fix is two-fold as following.
 
Create the function in the SQL Server as below.
    CREATE FUNCTION [dbo].[svf_CheckCountryIds](@CountryIds nvarchar(200)) 
    RETURNS bit AS 
    BEGIN 
    declare @valid bit 
    declare @rowsInserted INT 
    declare @addedCountryIds table([CountryId] nvarchar(200)) 
     
    insert into @addedCountryIds 
    select value from STRING_SPLIT(@CountryIds, ',') 
    set @rowsInserted = @@rowcount 
     
    if (@rowsInserted = (select count(a.CountryId) from @addedCountryIds a join [Country] b on a.CountryId = b.Id)) 
    begin 
    set @valid = 1 
    end 
    else 
    begin 
    set @valid = 0 
    end 
     
    RETURN @valid 
    END 


As you can see in the above function, we are passing the column data that is in the comma concatenated form and then they are split using STRING_SPLIT function and stored in the addedCountryIds table variable. Also, the inserted row count is stored in the rowsInserted variable.
 
Later, the values on addedCountryIds arejoined with Country table and if the count is matching, i.e., if all the passed country id is present in the Country table, true/1 is returned else false/0 is returned.
 
Create the FK with check constraint on the VisitedCountryIds as follows,
    ALTER TABLE Employee 
    ADD CONSTRAINT [FK_Employee_VisitedCountryIds] CHECK ([dbo].[svf_CheckCountryIds]([VisitedCountryIds]) = 1) 


As you can see constraint FK_Employee_VisitedCountryIds is created on VisitedCountryIds with condition that function svf_CheckCountryIds should return value as 1/true.
Now when you enter any country id other than 1 to 249, for example, if you enter VisitedCountryIds as '103,236,250', an error will be thrown as follows as id 250 is not the part of the country id list.
 
Msg 547, Level 16, State 0, Line 4
The INSERT statement conflicted with the CHECK constraint "FK_Employee_VisitedCountryIds". The conflict occurred in database "TestDb", table "dbo.Employee", column 'VisitedCountryIds'.
The statement has been terminated.
 
However, if you enter VisitedCountryIds as '103,236,249', it will be successfully inserted because all the ids are part of the country list.
 
I hope you found this post useful in handling the foreign keys in multivalued columns. Looking forward to your comments.



SQL Server 2019 Hosting - HostForLIFE.eu :: Store Multiple NULL Values With Unique Data In SQL Server

clock August 30, 2019 12:01 by author Peter

Sometimes, we get data that needs to be unique but we can also get NULL records. Existing ways to achieve uniqueness don’t allow NULLs (Primary Key) or allow a maximum of one NULL (Unique Constraint).
 
Let’s take an example to understand this better. Suppose, you have an Employee table with fields like Id, FirstName, MiddleName, LastName, Email, etc. As per the requirement, the email needs to be unique (if supplied), however, users are also allowed to register without entering their email and hence in the database Email is a nullable field.
 
So, how would you achieve the Email uniqueness having more than one NULL?

    CREATE UNIQUE NONCLUSTERED INDEX [UX_Employee_Email] ON [dbo].Employee WHERE Email IS NOT NULL 

The above code will ensure that the Email doesn’t have duplicate data, however, it may store more than one NULL.

 



SQL Server 2019 Hosting - HostForLIFE.eu :: How To Find Indian Financial Year And Financial Quarter From A Particular Date In SQL?

clock August 7, 2019 12:15 by author Peter

Here we will explain how to find the Indian financial year and financial quarter in a particular date with an example in SQL Server.  I have used the CASE statement and DATEPART() function to achieve this requirement.

DATEPART() in SQL Server
The DATEPART() function returns a specified part of a date, like – year, month, day, hour, minute, etc.

CASE Statement in SQL Server
CASE is the extension of IF ... ELSE statement. So, once a condition is true, it will stop reading & return the result. If no conditions are true, it returns the value in the ELSE block.
 
A) Find the FINANCIAL YEAR from date
 Write the below-given SQL code to find the financial year from given particular date,
    DECLARE@FilterDateASDATETIME 
    SET@FilterDate = GETDATE() 
    SELECTCASEWHENDATEPART(QUARTER,@FilterDate)= 1 THENYEAR(@FilterDate)ELSEYEAR(@FilterDate)+ 1 ENDAS[FINANCIAL_YEAR] 
    ** Note - @FilterDate - The date to be find the financial year


Output
Following is the result of the SQL query for financial year,

 
B) Find the FINANCIAL QUARTER from date
 
Write the below SQL code to find the financial Quarter from given particular date,
    DECLARE@FilterDateASDATETIME 
    SET@FilterDate = GETDATE() 
    SELECTCASEDATEPART(QUARTER, @FilterDate)WHEN 1 THEN'Q4'WHEN 2 THEN'Q1'WHEN 3 THEN'Q2'WHEN 4 THEN'Q3'ENDAS[FINANCIAL_QUARTER] 
    ** Note - @FilterDate - The date to be find the financial Quarter


Output
Following is the result of the SQL query for the financial quarter,



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