Sql-Server

When you run a query against SQL Server, you might want the rows to be returned in a specific order. However, the first thing you should ask yourself is whether that’s needed at all.

Sorting can be a very expensive operation if there is no suitable index that’s already sorted the data for you. And the question is: should SQL Server be the one doing the sorting? In many cases, the client application that’s reading the data might be a better place to do the sorting. That’s not always true but it’s worth considering. You often have way more clients than your single database server, and sorting data unnecessarily in the database server could limit your ability to scale your system to higher volumes.

2019-05-06

This is part 3 in a series of posts:

• Part 1 covered being sure there is a locking and blocking issue
• Part 2 covered the impact of RCSI

Today, though, I want to look at the next potential issue, and that’s indexing.

Indexing impacts on locking

It might seem obvious that you need to fix indexing issues in your database applications but it mightn’t be so obvious that locking is one of the main things that is affected.

2019-05-02

While doing my consulting work, I often come across Foreign Keys and Check Constraints that are not trusted. What this means is that either:

• They were created without checking existing data
• They were disabled for a period and re-enabled without re-checking the existing data

I like to see this fixed whenever possible. To make that easy, in our free SDU Tools for developers and DBAs, we added two stored procedures to help: RetrustForeignKeys and RetrustCheckConstraints.

2019-05-01

Look carefully at the following queries:

I’ve shown several examples here of what are called aliases. There are two basic types of aliases.

Column Alias

In the first query, I’ve used a column alias. I wanted to query the Description column in the dbo.Products table but I wanted the column called ProductName instead. So I follow the column with the word AS and then the name I want to use for the alias.

2019-04-29

This is part 2 in a series of posts:

• Part 1 covered being sure there is a locking and blocking issue

In part 1, I talked about pseudo locking and blocking issues that come from having queries running too long. I said that before you start fixing any locking and blocking issues, that you first need to make sure your queries are running fast. Today I want to discuss RCSI.

2019-04-25

When I’m writing utility scripts for SQL Server, I often need to make decisions or report on, details of the operating system that I’m running on. Unfortunately, SQL Server doesn’t have views that return this sort of information.

In our free SDU Tools for developers and DBAs, we added a series of views to help.

OperatingSystemConfiguration has details of OperatingSystemRelease, OperatingSystemName, ServicePackLevel, OperatingSystemSKU, OperatingSystemSKUName, and LanguageName.

OperatingSystemVersions has details of OS_Family, OS_Version, and OS_Name.

2019-04-24

We all see news articles talking about how company after company exposed private details of their clients, customers, and sometimes, even staff. In so many cases, a reasonable approach to encryption would have avoided these issues. Time and again though, I see people doing dodgy work on protecting their data; some even trying to roll their own protection.

Don’t do this!

Encryption is one of the most important yet least understood technologies in SQL Server. It’s improved so much over the years and 2019 makes it even better.

2019-04-23

If you look carefully at the following simple query:

you’ll notice that I didn’t just say FROM Cinemas, I said FROM dbo.Cinemas. The “dbo.” part is the name of the schema. I talked about schemas in an earlier post. And all through these T-SQL 101 blog posts, I keep mentioning that you should always use the schema name as well as the object name.

By why?

2019-04-22

According to Wikipedia, Betteridge’s law of headlines is an adage that states: “Any headline that ends in a question mark can be answered by the word no.” In this case, they’re correct because the answer is no. But as with most things in this industry, there are subtle issues with that answer.

In SQL Server, a view is just a SELECT statement that’s been given a name. That’s pretty much it. No data is stored, and every time you access the view, the query optimizer expands the view into the surrounding query. By the time you get to an execution plan, the view is nowhere to be found.

2019-04-19

I get lots of requests to help customers with their SQL Server systems. Many, many requests start with customers asking me if I can help them fix their blocking issues. Most customers aren’t actually aware of true blocking issues. Invariably what they mean, is that they’ve started to have deadlocks and things are blowing up.

Is blocking really the issue?

I always start by working out if they really have a blocking issue. When I see performance problems, after eliminating obvious hardware and configuration issues, I’d say the issues fall into these buckets:

2019-04-18