How To Run SQL Scripts Via Command Prompt

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Usually, when we run SQL scripts, it is done on an ad hoc basis.  We usually run one file at a time just once.  From time to time there is the need to run a set of SQL script files.  One common reason I’ve seen for doing this is to rebuild a database for testing.  If you had all of your create tables/stored procedure commands stored in a series of SQL script files, then you could rebuild your database fairly easily by executing the SQL files in sequence.

 
SQL Server provides a tool to do this called SQLCMD.

The sqlcmd utility lets you run entire SQL script files full of t-sql via command prompt.  Leveraging this tool, you can create a batch file to run the sql script files in sequence.

 
 
How To Execute A SQL Script File Via Command Prompt With SQLCMD

Although there are TONS of command line options for executing a sql script.  Just executing a sql script file with the basic options is very easy.

The above command uses the -i option to specify the input file of DropTables.sql.  Everything inside this file will be execute on the current database.

 
NOTE: When you create your SQL script files, I always recommend putting a USE statement at the top of your script.  This will ensure that you are using the correct database when your dropping and creating tables.

 
 
Run A Batch Of SQL Script Files

Now that you know how to run one SQL script file… running multiple should be easy.  All you need to do is create a batch file and run one script after the other.

 
Your batch file will look something like this:

 
 
What About Errors?

So what happens if the SQL script file throws an error?  The above commands I showed you will just ignore any errors.  If you want to capture your errors, you need to add the command line option /b.  This flag will tell the sqlcmd utility to stop processing the script and output a DOS ERRORLEVEL value.  You can then check the DOS ERRORLEVEL value after each execution.

 
 
Reference: http://msdn.microsoft.com/en-us/library/ms162773.aspx

 

SQL Server Trim

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SQL Server trim function does not exist!  Although this seems a bit odd, SQL Server does somewhat have support for trimming data.  SQL Server has built in functions for Right Trim and for Left Trim.  Using these functions, you can accomplish a full trim.  I’ll first show you how to trim the different sides of the text and then show how to trim the full thing.

 
Trim Text Inline

The functions to trim text are RTrim() and LTrim().

 
If a full trim is something that you do often, you can create a SQL Server Trim function to make the process a little simpler.

You can use this new fancy SQL Server Trim function by calling it like this:

Option Recompile

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Option recompile is one of those hidden gems when it comes to increasing stored procedure performance.  When used in the right spot, this can speed up a never ending stored procedure call to instantaneous.  If you don’t know what option recompile is… it’s just a query hint that can be added to the end of a sql query.

What Option Recompile Does

When option recompile is added to the query hints, it does a couple things.  The first thing that it does is it tells SQL Server to discard any stored execution plan for that query.  This will cause SQL Server to rebuild the execution plan for this query.  The next thing it does is the magical part.  When SQL Server goes to build the execution plan, it will replace the local variables with the actual values in those variables.  This allows SQL Server to pull the data SUPER fast.

Symptoms

Keep in mind that many times the slowdown in a stored procedure call is just one statement inside the stored procedure.

The easiest way that I have found to figure out if this will help a slow stored procedure is to decompose the stored procedure in to separate sql statements.  I then run the sql statements to see what one is the slow one.  If I run a statement that is slow and uses a local variable, this may be a good candidate.  Next I replace the local variables in that statement with the explicit values.  If I rerun the statement and it performs fast, I know that this could use option recompile.

Syntax

Rebuild Execution Plan

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One way that SQL Server optimizes stored procedure execution time is by caching the execution plan.  This functionality is built-in to SQL Server and is done every time that you create a stored procedure.

What Is An Execution Plan?

An execution plan in SQL Server is simply the way that SQL Server will go about getting the data for the client.  When a query is executed in SQL Server, it will generate an execution plan.  This execution plan is a set of steps that is the most efficient way to get this data from the database for the user.

How Do You Know If You Need To Rebuild An Execution Plan?

Okay, this is not very scientific.  Usually what I’ve found in the past is that when a stored procedure runs fast one day… and the next day it is running slow… one cause might be that the execution plan needs to be rebuilt.

How To Rebuild An Execution Plan?

If you think that a stored procedure in your database has an execution plan that is not the most efficient, here are a couple easy ways to rebuild the execution plan.  Keep in mind that the following queries do not actually rebuild the execution plan.  They merely force the stored procedure to rebuild the execution plan next time that it is executed.

Rebuild For One Specific Stored Procedure

In the example below, CustOrderHist is the name of the stored procedure we want to rebuild the execution plan for.

Rebuild All Execution Plans For All Stored Procedures On Your Server

NOTE: The WITH NO_INFOMSGS option will suppress a generic message that comes up after executing the FREEPROCCACHE command.

Why Does This Happen?

As data changes in your database, the data in the index will change as well.  As the statistics for an index change, what used to be the fastest way to pull data may no longer be the fastest way.

Automatic Rebuild Of The Execution Plan

Of course SQL Server does not require you to always rebuild the execution plans manually.  There are triggers in the database that will cause an automatic rebuild of the execution plan.

  • Alterations to the table, view, stored procedure, or indexes used by the stored procedure
  • Updating statistics on the table or index that the stored procedure uses
  • Dropping an index used by the stored procedure
  • A lot of inserts or deletes from a table (causing a large change in the keys)
  • Executing a stored procedure with the WITH RECOMPILE option

Reference: http://technet.microsoft.com/en-us/library/ms181647.aspx  –  sp_recompile (Transact-SQL)
Reference: http://technet.microsoft.com/en-us/library/ms174283(v=sql.105).aspx  –  DBCC FREEPROCCACHE (Transact-SQL)