16May 2016 by Grant Fritchey 8 Comments

Query Store, Forced Plans, and New Plans

Azure, SQL Server 2016
I love questions. I recently received one about new plans in the Query Store (available in Azure SQL Database now and in SQL Server 2016 after June 1). Let's say you have selected a plan that you want to force. You set it up. Now, let's say the plan ages out of cache or even goes through a recompile. During the recompile, due to out of date statistics or skew in the statistics, you would, under normal circumstances, get a new plan. However, with Query Store and plan forcing, the plan that's going to be used is the plan that is being forced. But, does that other plan, the one not used, get stored in Query Store? I have no idea. Let's find out. The Setup To start with, a small stored procedure…
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12May 2016 by Grant Fritchey 9 Comments

Use The Correct Data Type

SQL Server, SQL Server 2016, T-SQL
Blog post #5 in support of Tim Ford’s (b|t) #iwanttohelp, #entrylevel. Read about it here. Saying that you should use the correct data type seems like something that should be very straight forward. Unfortunately it's very easy for things to get confusing. Let's take a simple example from AdventureWorks. If I run this query: SELECT a.ModifiedDate FROM Person.Address AS a WHERE a.AddressID = 42; The output looks like this: 2009-01-20 00:00:00.000 Normal right? You see the year, the month and the day followed by the time in hours, minutes, and seconds as a decimal. Ah, but there is an issue. This query is supposed to be for the reporting system, and the business only cares about the date that the values in the Person.Address table have been modified, so they don't want…
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03May 2016 by Grant Fritchey 5 Comments

Implicit Conversion and Performance

SQL Server, SQL Server 2016, T-SQL
Letting SQL Server change data types automatically can seriously impact performance in a negative way. Because a calculation has to be run on each column, you can't get an index seek. Instead, you're forced to use a scan. I can demonstrate this pretty simply. Here's a script that sets up a test table with three columns and three indexes and tosses a couple of rows in: CREATE TABLE dbo.ConvertTest ( BigIntColumn BIGINT NOT NULL, IntColumn INT NOT NULL, DateColumn VARCHAR(30) ); CREATE INDEX BigIntIndex ON dbo.ConvertTest (BigIntColumn); CREATE INDEX IntIndex ON dbo.ConvertTest (IntColumn); CREATE INDEX DateIndex ON dbo.ConvertTest (DateColumn); WITH Nums AS (SELECT TOP (1000000) ROW_NUMBER() OVER (ORDER BY (SELECT 1 )) AS n FROM master.sys.all_columns ac1 CROSS JOIN master.sys.all_columns ac2 ) INSERT INTO dbo.ConvertTest (BigIntColumn, IntColumn, DateColumn ) SELECT Nums.n, Nums.n,…
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12Apr 2016 by Grant Fritchey 8 Comments

A View Is Not A Table

Azure, SQL Server, SQL Server 2016, T-SQL
Blog post #4 in support of Tim Ford’s (b|t) #iwanttohelp, #entrylevel In SQL Server, in the T-SQL you use to query it, a view looks just like a table (I'm using the AdventureWorks2014 database for all these examples): SELECT * FROM Production.vProductAndDescription AS vpad;   SELECT vpad.Name, vpad.Description, vpmi.Instructions FROM Production.vProductAndDescription AS vpad JOIN Production.Product AS p ON p.ProductID = vpad.ProductID JOIN Production.vProductModelInstructions AS vpmi ON vpmi.ProductModelID = p.ProductModelID WHERE vpad.ProductID = 891 AND vpad.CultureID = 'fr'; The above query actually combines two views and a table. This is what is commonly referred to as a "code smell". A code smell is a coding practice that works, but that can lead to problems. In this case, we're talking about performance problems. The performance problems when using views to join to…
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05Apr 2016 by Grant Fritchey 3 Comments

Views and Simplification

SQL Server, SQL Server 2016, T-SQL
I've been getting lots of questions on views lately. Must be something in the water. Because SQL Server allows you to treat a view as if it was a table, lots of people pretty much assume that it is a table since they get to treat it that way. The thing is, a view is not a table. It's a query. Let's explore this just a little bit. Here's a relatively straight forward view: CREATE VIEW dbo.PersonInfo AS SELECT a.AddressLine1, a.City, a.PostalCode, a.SpatialLocation, p.FirstName, p.LastName, be.BusinessEntityID, bea.AddressID, bea.AddressTypeID FROM Person.Address AS a JOIN Person.BusinessEntityAddress AS bea ON a.AddressID = bea.AddressID JOIN Person.BusinessEntity AS be ON bea.BusinessEntityID = be.BusinessEntityID JOIN Person.Person AS p ON be.BusinessEntityID = p.BusinessEntityID; GO I can query this view like this: SELECT * FROM dbo.PersonInfo AS pni…
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28Mar 2016 by Grant Fritchey 8 Comments

Query Store and Optimize For Ad Hoc

SQL Server 2016
I love presenting sessions because you get so many interesting questions. For example, what happens with Optimize for Ad Hoc when Query Store is enabled? Great question. I didn't have the answer, so, on to testing. For those who don't know, Optimize for Ad Hoc is a mechanism for dealing with lots and lots of ad hoc queries. When this is enabled, instead of storing an execution plan the first time a query is called, a plan stub, basically the identifying mechanisms, for the plan is stored in cache. This reduces the amount of space wasted in your cache. The second time the query is called, the plan is then stored in cache. I'm going to set up Optimize for Ad Hoc and Query Store and, to clean the slate,…
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07Mar 2016 by Grant Fritchey 2 Comments

SQL Server Backups Are A Business Decision

SQL Server, SQL Server 2016
Blog post #3 in support of Tim Ford’s (b|t) #iwanttohelp, #entrylevel Read more about Tim's challenge here. It's very easy to think of SQL Server backups as a technical problem. You have so much stuff going on, BACKUP DATABASE commands, recovery models, BACKUP LOG commands, Differential backups. Getting them all into the correct order and automating the processes sure seems like a technical problem. It isn't. It's all about the business. If you're taking on the duties of a DBA whether you're an accidental DBA, a reluctant DBA or you were voluntold into the DBA position, you need to plan to sit down with responsible parties from the business and get an understanding with them regarding RPO and RTO. RPO is a TLA for Recovery Point Objective. The easiest way to…
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12Jan 2016 by Grant Fritchey No Comments

“Applies To…” in the MSDN Documentation

Azure, SQL Server 2016, T-SQL
Quick little post. I just wanted to share how happy I am with the new "THIS TOPIC APPLIES TO" infographic. An example here: I think it makes things much more clear when you're attempting to figure out what's up with some T-SQL syntax. Well done Microsoft and thank you. Side note, this only exists in documentation that has been updated recently. I first saw it in some documentation that was updated January 11, 2016. It's not there in another piece of documentation I saw that was updated October 15, 2015. Here's hoping it gets put everywhere. It works.
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20Oct 2015 by Grant Fritchey No Comments

Statistics for the New Data Pro

PASS, SQL Server, SQL Server 2016, T-SQL
Next week at the PASS Summit I'll be presenting a session called Statistics for the New Data Pro. You can read the abstract at the link. I just want to emphasize that this is a beginner level session. I think way too many people who are just starting out with SQL Server don't understand the role that statistics play in determining how your queries are going to behave. What's more, too many people don't know how to get and read statistics to understand how it is that the optimizer thinks you have X number of rows in your database that match a given value. I'm going to make darned sure that the people who attend this session come out with a full understanding of how to read the statistics. This includes…
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13May 2014 by Grant Fritchey 8 Comments

Add an Instance to SQL Server Azure Virtual Machine

Azure, SQL Server
How do you add an instance to your local SQL Server installation? You run the executable that you probably downloaded from MSDN or maybe from a CD. Works the same on an Azure VM right? Sure... but wait. Do I have to go and download the software to my VM instance? Let's assume that you're running one of the VMs from the Gallery, then, the answer is "No." Just navigate to C:\SQLServer_12.0_Full. There you'll find the full installation setup for SQL Server. And you're off and running... Until you realize that you don't have the Product Key for this thing. What happens when you get to this screen: You can look around all you want and you won't see a product key anywhere. At least no where that I could…
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