SQL Server Nested Select

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SQL Server nested select is also known as a “sub query”. This is where instead of using a list, table, or view, you actually use another query. In this article, we will go over the basics on how to use a SQL Server nested select statement.

Basic Rules For A Nested Select
Here are a couple basic rules when using a nested select statement in SQL Server.

  • The nested select statement must be enclosed in parentheses.
  • When using an ORDER BY clause in your nested select, you must specify TOP command.
  • Many times, you will need to alias the nested select.

 
Sample Nested Select
Here is a sample where we return the basic animal information with their average weight.

In the above example, we do our normal inner join, but we join to a nested select statement. This allows you to join on the results from the nested select. You can see that the nested select statement will get the average weight of the animals by AnimalID. That whole query is inside parenthesis. Then we alias that nested select results as “W”. We can then reference the 2 return values (AnimalID and AverageWeight) outside of the nested select statement by using the table alias W.

 
 
NOTE: Remember that you will need to alias your nested select statements most of the time. This can stop you up if you aren’t looking for it.

SQL Server Kill All Connections

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Killing all connections in SQL Server is something that you may need to do from time to time. The two times that I’ve needed to do this most is when I’m restoring a database in my test environment or when I need to rename a database. Both of these operations require that there are not any open connections to the SQL Server database. There are a couple good scripts that I will show here. My favored method is to set it in single user mode.

 
Kill All Connections Using Single User Mode
This is the easiest way kill all the connections to the database. It basically sets the database to only allow 1 user (you) and it will kill all the other connections.

 
Kill All Connections Using The Kill Command
The following query will loop through all the open processes on the database and kill each one. Note that this may take a little bit of time to execute if there are long running transactions, it may take some time to roll them back.

 
Reference: https://msdn.microsoft.com/en-us/library/bb522682(v=sql.105).aspx
https://msdn.microsoft.com/en-us/library/ms173730.aspx

Script Multiple Objects [Easy]

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Have you ever noticed that you can only highlight 1 object in the Object Explorer in SQL Server Management Studio? This usually is enough for most things you do, but if you want to script multiple objects at once… it becomes a pain. Well there is a way to script multiple objects at once, and it’s super easy.

  1. Open the Object Explorer Details screen by selecting View -> Object Explorer Details.
    Script Multiple Objects 1
  2. Highlight the folder with the objects that you would like script. A list of all objects in that folder will appear on the right. This works for tables, stored procedures, etc…
    Script Multiple Objects 2
  3. Highlight all the objects that you want, right click, and select Create To.
    Script Multiple Objects 3

JSON In SQL Server

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Finally in SQL Server 2016, Microsoft SQL Server now supports JSON serialization. It provides it through the FOR clause… like XML serialization. This will take a recordset and output it in JSON format with very little effort by the coder.

As you can see. To get the output to come in JSON format, all you need to do is add FOR JSON PATH at the end of your query. Simple right? Here is what the results would look like.

Adding All Columns In A Table To A Query [Easy]

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I wanted to share this quick tip with you on how to add a list of all the columns in a table to your query window in SQL Server Management Studio. This is the easiest way I know!

  1. Expand the Object Explorer to show the table that you want to add the columns for.
        Adding All Columns 1
  2. Select the Columns folder on to your query window.
        Adding All Columns 2
  3. Drag the whole folder on to your query window and just drop it where you want it. That’s it!
    Adding All Columns 3