I was working with a client and they had set up one sql server for an ETL process. When we tried to get the data from  the database we got the error:
"Could not find server 'server name' in sys.servers in SQL Server"

How to resolve this
First you need to check if the server exists in sys servers,
select name from sys.servers 

You will get the servers list here, if the server does not exist in the list, then add it using the command,
EXEC sp_addlinkedserver @server = 'New_Server_Name' 

Once the server is added to the linked server, then you can log in like this,
EXEC sp_addlinkedsrvlogin 'New_Server_Name','false',NULL,'USERNAME','PASSWORD' 

Now you can do whatever you want to do, you can use your local server now,
exec [New_Server_Name].[Database_Name].dbo.Procedure_NAME

Finally, you can drop this server from the linked server list using this command,
sp_dropserver 'New_Server_Name', 'droplogins' 

There's so many new capabilities to play around and explore in SQL Server 2019. One of the new capabilities that has caught our attention is the introduction of JSON support. In this post, I will get started in creating a JSON document using SQL Server 2019.

SQL Server 2016 will support JSON (JavaScript Object Notation). JSON is an open, text-based exchange format based on JavaScript’s object literal notation. JSON is a popular data-interchange format used in modern web and mobile applications, as well for storing unstructured data. It is supported in several DB/NoSQL engines and this improvement will enable developers to put some JSON processing logic in the SQL Server that will enable them to parse, query, analyze, and update JSON data.

Step 1

In this post, you will query a standard table and then convert it into JSON format. For this example, you are querying the standard AdventureWorks database:

SELECT TOP(2) PP.[PersonType], PP.[FirstName], PP.[MiddleName], PP.[LastName], EA.[EmailAddress]
FROM Person.Person PP
INNER JOIN [Person].[EmailAddress] EA
ON EA.[BusinessEntityID] = PP.[BusinessEntityID]

Sample output for rows inside SQL Server Management Studio looks like below:

Step 2

Now, you will add the FOR JSON AUTO support to get the same output in JSON format.

SELECT TOP(2) PP.[PersonType], PP.[FirstName], PP.[MiddleName], PP.[LastName], EA.[EmailAddress]
FROM Person.Person PP
INNER JOIN [Person].[EmailAddress] EA
ON EA.[BusinessEntityID] = PP.[BusinessEntityID]
FOR JSON AUTO

The output looks like below:

[
{
"PersonType":"EM",
"FirstName":"X",
"MiddleName":"Y",
"LastName":"Z",
"EA":[{"EmailAddress":"[email protected]"}]
},
{"PersonType":"EM",
"FirstName":"A",
"MiddleName":"B",
"LastName":"C",
"EA":[{"EmailAddress":"[email protected]"}]
}
]

Step 3

You can also generate JSON using the PATH option like:

SELECT TOP(2) PP.[PersonType], PP.[FirstName], PP.[MiddleName], PP.[LastName], EA.[EmailAddress]
FROM Person.Person PP
INNER JOIN [Person].[EmailAddress] EA
ON EA.[BusinessEntityID] = PP.[BusinessEntityID]
FOR JSON PATH

The output for this query would look little different like:

[
{"PersonType":"EM", "FirstName":"X”, “MiddleName":"Y”, “LastName":"Z”, “EmailAddress":"[email protected]"},{"PersonType":"EM”, “FirstName":"A”, “MiddleName":"B”, “LastName":"C”, “EmailAddress":"[email protected]"}
]

Now that you are able to generate few simple output using JSON keyword.

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Hi all, In this blog, I will explain to you how to apply a script or a query to multiple databases in a single execution using a database name. I get all database names, create a loop, and execute a command that I want to do.

Here I am using 2 databases, EnterpriseGL and GR8. I get all database names using a loop, and after that, I get database names one by one, put a script with a name, and execute the script.
  BEGIN TRAN 
    
  CREATE TABLE #TempGETDBLIST 
     ( 
        [NAME] NVARCHAR(255) NULL, 
        [ROWID] INT IDENTITY NOT NULL 
     ) 
           INSERT INTO #TempGETDBLIST (NAME) 
    
        --unomment which database use want to apply 
       --SELECT NAME FROM master.dbo.sysdatabases WHERE name like '%EnterpriseGL%'  -- get all GL databases 
        --SELECT NAME FROM master.dbo.sysdatabases WHERE name like '%GR8%' --get all GR8 databases 
    
          SELECT '#TempGETDBLIST',* FROM #TempGETDBLIST 
           DECLARE @Flag INT = 1 
    
  WHILE (@Flag <= (SELECT COUNT(1) FROM #TempGETDBLIST)) 
  BEGIN 
        DECLARE @ABC NVARCHAR(50), @query NVARCHAR(max) 
        SET @ABC =(SELECT Name FROM #TempGETDBLIST WHERE ROWID = @Flag) 
        SET @query = 'USE '+ @ABC +' select top 1 * from SystemConfiguration' 
    
     EXECUTE( @query ) 
     SET @Flag = @Flag + 1 
    
  END 
    
  DROP TABLE #TempGETDBLIST 
  ROLLBACK TRAN

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The SQL 'Is Null' statement returns the specified value if the expression is NULL, otherwise, it returns the expression. If the expression is NOT NULL, then this function returns the expression.

Syntax
    SELECT ISNULL(NULL, 'Csharpcorner');   

This replaces Null with the specified replacement value. 
 
A null statement doesn't specify that the Boolean result is negated. The predicate reverses its return values, returning True if the value is not Null, and False if the value is a Null statement.
 
Syntax
    ISNULL ( check_expression , replacement_value ) 

This is the expression returned if the check_expression is NULL. The replacement_value must be of a type that is implicitly convertible to the type of check_expression.
 
Using IsNull with Avg in SQL statement
 
The following example finds the average of the OrderDetails.  It substitutes the value 8 for all NULL entries in the orderId column of theOrderDetails table.
 
Syntax
    USE sample ;     
    GO     
    SELECT AVG(ISNULL(OrderId, 8))     
    FROM OrderDetails ;     
    GO     

Example

Using ISNULL in SQL
The following example selects the description, discount percentage, minimum quantity, and maximum quantity for all special offers in the sample. If the maximum quantity for a particular special offer is NULL, the MaxQty shown in the result set is 0.00. 
 
Syntax
    USE sample ;     
    GO     
    SELECT OrderId , OrderName, Orderaddress , ISNULL(OrderId, 0.00) AS 'Max Quantity'     
    FROM OrderDetails;     
    GO   

Testing for NULL in a Where clause
Do not use ISNULL to find NULL values; use IS NULL instead. The following example finds all OrderDetails that have NULL in the ordername, orderAddress, OrderDate  column. Note the space between IS and NULL.
 
Syntax
    -- Uses sample     
    SELECT OrderName, orderAddress, OrderDate     
    FROM  OrderDetails     
    WHERE OrderId  IS NULL;  

A SQL cursor is a database object that is used to retrieve data from a result set one row at a time. A SQL cursor is used when the data needs to be updated row by row. This article explains everything about SQL cursors. In this article, we will learn the following:

•     Introduction to SQL cursor
•     Cursor life cycle
•     Why and when use a cursor
•     How to implement cursors
•     What are the limitation of SQL cursor
•     How can we replace a SQL Cursor

SQL Cursor Life Cycle
The following steps are involced in a SQL cursor life cycle.

    Declaring Cursor
    A cursor is declared by defining the SQL statement.

    Opening Cursor
    A cursor is opened for storing data retrieved from the result set.

    Fetching Cursor
    When a cursor is opened, rows can be fetched from the cursor one by one or in a block to do data manipulation.

    Closing Cursor
    The cursor should be closed explicitly after data manipulation.

    Deallocating Cursor
    Cursors should be deallocated to delete cursor definition and release all the system resources associated with the cursor.

Why use a SQL Cursor?
In relational databases, operations are made on a set of rows. For example, a SELECT statement returns a set of rows which is called a result set. Sometimes the application logic needs to work with one row at a time rather than the entire result set at once. This can be done using cursors.

In programming, we use a loop like FOR or WHILE to iterate through one item at a time, the cursor follows the same approach and might be preferred because it follows the same logic.
SQL Cursor Syntax
    DECLARE cursor_name CURSOR [ LOCAL | GLOBAL ]  
    [ FORWARD_ONLY | SCROLL ] 
     [ STATIC | KEYSET | DYNAMIC | FAST_FORWARD ]  
    [ READ_ONLY | SCROLL_LOCKS | OPTIMISTIC ]  
    [ TYPE_WARNING ] FOR select_statement 
     [ FOR UPDATE [ OF column_name [ ,...n ] ] ] [;]  

Cursor Example
The following cursor is defined for retrieving employee_id and  employee_name from Employee table.The FETCH_STATUS value is 0 until there are rows.when all rows are fetched then  FETCH_STATUS becomes 1.
    use Product_Database 
    SET NOCOUNT ON;   
     
    DECLARE @emp_id int ,@emp_name varchar(20),   
        @message varchar(max);   
     
    PRINT '-------- EMPLOYEE DETAILS --------';   
     
    DECLARE emp_cursor CURSOR FOR    
    SELECT emp_id,emp_name   
    FROM Employee 
    order by emp_id;   
     
    OPEN emp_cursor   
     
    FETCH NEXT FROM emp_cursor    
    INTO @emp_id,@emp_name   
     
    print 'Employee_ID  Employee_Name'      
     
    WHILE @@FETCH_STATUS = 0   
    BEGIN   
        print '   ' + CAST(@emp_id as varchar(10)) +'           '+ 
            cast(@emp_name as varchar(20)) 
     
         
        FETCH NEXT FROM emp_cursor    
    INTO @emp_id,@emp_name   
      
    END    
    CLOSE emp_cursor;   
    DEALLOCATE emp_cursor;   

The Output of the above program will be as follows

SQL Server
What are the limitations of a SQL Cursor

A cursor is a memory resident set of pointers -- meaning it occupies memory from your system that may be available for other processes.

Cursors can be faster than a while loop but they do have more overhead.

Another factor affecting cursor speed is the number of rows and columns brought into the cursor. Time how long it takes to open your cursor and fetch statements.

Too many columns being dragged around in memory, which are never referenced in the subsequent cursor operations, can slow things down.

The cursors are slower because they update tables row by row.
How can we replace SQL Cursors
There's one replacement for cursors in SQL server joins.

Suppose we have to retrieve data from two tables simultaneously by comparing primary keys and foreign keys. In these types of problems, the cursor gives very poor performance as it processes through each and every column. On the other hand using joins in those conditions is feasible because it processes only those columns which meet the condition. So here joins are faster than cursors.

The following example explains the replacement of cursors through joins.

Suppose, we have two tables, ProductTable and Brand Table. The primary key of BrandTable is brand_id which is stored in ProductTable as foreign key brand_id. Now suppose, I have to retrieve brand_name from BrandTable using foreign key brand_id from ProductTable. In these situations cursor programs will be as follows,
    use Product_Database 
    SET NOCOUNT ON;   
     
    DECLARE @brand_id int    
    DECLARE @brand_name varchar(20)  
     
     
    PRINT '--------Brand Details --------';   
     
    DECLARE brand_cursor CURSOR FOR    
    SELECT distinct(brand_id) 
    FROM ProductTable;  
     
    OPEN brand_cursor   
     
    FETCH NEXT FROM brand_cursor    
    INTO @brand_id   
     
    WHILE @@FETCH_STATUS = 0   
    BEGIN   
        select brand_id,brand_name from BrandTable where brand_id=@brand_id 
    --(@brand_id is of ProductTable) 
         
        FETCH NEXT FROM brand_cursor    
    INTO @brand_id  
      
    END    
    CLOSE brand_cursor;   
    DEALLOCATE brand_cursor;   

The Output of the above program will be as follows

SQL Server
The same program can be done using joins as follows,
Select distinct b.brand_id,b.brand_name from BrandTable b inner join
ProductTable p on b.brand_id=p.brand_id

The Output of the above program will be as follows

SQL Server
As we can see from the above example, using joins reduces the lines of code and gives faster performance in case huge records need to be processed.