Sql-Server

There is a SQL Server T-SQL function that calculates the number of days (or months, or years, or other time periods) between any two dates.

SELECT DATEDIFF(day, ‘firstdate’, ‘seconddate’);

But I regularly get asked how to work out the number of days between two dates, excluding the weekends (Saturday and Sunday).

I’ve seen a few functions around that do a pretty good job at this but many don’t work properly if you have DATEFIRST changed in your session ie: if you change the first day of the week.

2017-11-15

Most of the time, we want SQL Server T-SQL queries to run as fast as possible, just the same as we want programs in any programming language to run as fast as possible.

But there are times when you want SQL Server to just sleep for a while, and without tying up system resources (like spinning around on the CPU).

Example of this would be waiting for new entries in Service Broker queues, or waiting to retry deadlocks.

2017-11-10

This is a really popular shortcut in SQL Server Management Studio (SSMS) but I continue to be amazed how many people aren’t aware of it.

Object Explorer is a very useful part of SSMS and you can drag pretty much any name that you see in it, across to a query window.

You could do the same for each column in the Columns list.

You might also realize that you can hover over the asterisk and see a list of columns:

2017-11-09

I love it when SQL Server gets brand new T-SQL language features.

SQL Server 2017 added a great new language feature called TRANSLATE. It’s been in some other products like Oracle for a while but it’s just been added to SQL Server.

Imagine I have a string like this:

’[02] 9992:2343’ 

But what I really want is one like this:

’(02) 9992-2343’

Up to SQL Server 2016, I could do this with a series of replace statements:

2017-11-08

Many people know that I have an issue with ORMs (object relational mappers). It’s worth spending a blog post to describe why.

Unfortunately, I spend my life on the back end of trying to deal with the messes involved. The following are the key issues that I see:

Potentially horrid performance

I’ve been on the back end of this all the time. There are several reasons. One is that the frameworks generate horrid code to start with, the second is that they are typically quite resistant to improvement, the third is that they tend to encourage processing with far too much data movement.

2017-11-07

Occasionally I run into a need to clear out all objects in a schema in a SQL Server database. Sometimes it’s because I want to remove the schema itself. It’s often painful to do as I have to find all the types of T-SQL objects, and then often have to remove them in a particular order.

So I added a tool to my SDU Tools collection to do just that.

2017-11-03

I recently shipped the latest update to my SDU Tools collection.

This time I decided to add a tool that’s in the “cute” category. It’s called InvertString and you can see it action in the image above.

Yes, it takes an input string and returns a string that looks quite like an upside down version of the same string.

As part of the inversion I also reversed the order of the string so when you look at it upside down, it still looks correct. But if what you really want is a mirror image, you could combine it with REVERSE to achieve that outcome:

2017-10-31

I spend most of my life in a variety of customer sites. Most of these nowadays tend to be large financial organizations. When I talk to developers in those organizations, and ask them about how they interact with their DBAs, I can’t tell you how often I hear that they try to avoid ever making schema changes, etc. as it takes too long and the process is painful.

When I talk to the DBAs at the same organizations, and I ask them why they resist making schema changes, I hear this:

2017-10-27

GUIDs (uniqueidentifiers in SQL Server) are well understood to cause fragmentation issues when used as clustering keys for SQL Server tables. It’s easy to understand why, but is NEWSEQUENTIALID the answer? I don’t think so. Here’s why.

When a SQL Server table has a clustered index, it needs to maintain the logical sequence of rows in the order of the clustering key. There are a few important notes here:

• I’ve mentioned key, not column. The key might involve more than one column.
• I’m not talking about primary keys. While the default for SQL Server is to make primary keys clustered if there isn’t already another clustering key, primary keys are a logical construct unrelated to how the table data is stored.
• I’m not talking about physical storage. I often hear people say that clustered indexes determine how data is physically stored. That was in old Microsoft courseware, etc. and just isn’t true. It’s about logical ordering. If not, there would be no fragmentation and changing the data would take forever.
• The problem with using GUIDs as clustering keys is that they are typically generated in a random order using a function like NEWID() or using a function like System.Guid.NewGuid() in .NET (or similar functions in other languages).

Let’s take a look at this by creating a table and populating it:

2017-10-26

I recently posted that I was moving to this new blog and wanted to thank Adam Machanic and Peter DeBetta.

Well I need to thank Adam Machanic even more. I was intending to just start the new blog from scratch and leave the old one in place but Adam was working on code to help to migrate to WordPress-based engines from Community Server, so he offered to let me Alpha test it.

2017-10-20