Blog Archives

Installing SQL Server 2016 Language Reference Help from disk

A couple of years ago I blogged about Installing the SQL Server 2014 Language Reference Help from disk.

With SQL Server 2016 things changed significantly: we have the new Help Viewer 2.2, which is shipped with the Management Studio setup kit.

However, despite all the changes in the way help works and is shipped, I am still unable to download and install help content from the web, so I resorted to using the same trick that I used for SQL Server 2014.

This time the URLs and the files to download are different:

    1. Point your browser to
    2. Download the Language Reference Files:

      If you’re a PowerShell person, these three lines will do:

Invoke-WebRequest -Uri "" `
	-OutFile "sql_2016_branding_en-us(1bd6e667-f159-ac3b-f0a5-964c04ca5a13).cab"
Invoke-WebRequest -Uri "" `
	-OutFile "v2sql_shared_language_reference_b4621_sql_130_en-us_1(83748a56-8810-751f-d453-00c5accc862d).cab"
Invoke-WebRequest -Uri "" `
	-OutFile "v2sql_shared_language_reference_b4621_sql_130_en-us_2(ccc38276-b744-93bd-9008-fe79b294ff41).cab"
      1. Create a text file name HelpContentSetup.msha in the same folder as the .cab files and paste the following html:
<html xmlns="">
<head />
<body class="vendor-book">
    <div class="details">
        <span class="vendor">Microsoft</span>
        <span class="locale">en-us</span>
        <span class="product">SQL Server 2016</span>
        <span class="name">Microsoft SQL Server Language Reference</span>
    <div class="package-list">
        <div class="package">
            <span class="name">SQL_2016_Branding_en-US</span>
            <span class="deployed">False</span>
            <a class="current-link" href="sql_2016_branding_en-us(1bd6e667-f159-ac3b-f0a5-964c04ca5a13).cab">sql_2016_branding_en-us(1bd6e667-f159-ac3b-f0a5-964c04ca5a13).cab</a>
        <div class="package">
            <span class="name">v2SQL_Shared_Language_Reference_B4621_SQL_130_en-us_1</span>
            <span class="deployed">False</span>
            <a class="current-link" href="v2sql_shared_language_reference_b4621_sql_130_en-us_1(83748a56-8810-751f-d453-00c5accc862d).cab">v2sql_shared_language_reference_b4621_sql_130_en-us_1(83748a56-8810-751f-d453-00c5accc862d).cab</a>
        <div class="package">
            <span class="name">v2SQL_Shared_Language_Reference_B4621_SQL_130_en-us_2</span>
            <span class="deployed">False</span>
            <a class="current-link" href="v2sql_shared_language_reference_b4621_sql_130_en-us_2(ccc38276-b744-93bd-9008-fe79b294ff41).cab">v2sql_shared_language_reference_b4621_sql_130_en-us_2(ccc38276-b744-93bd-9008-fe79b294ff41).cab</a>
      1. First, set the Help Viewer to open help from the local sources:
      2. Then select the “Add and Remove Help Content” command:
      3. This command opens the Help Viewer and asks for the content to add.
        Browse to the file you created in step 3.
        Click “Add” on all the items you wish to add to the library. In this case you will have only 1 item.
        When done, click the “Update” button.
      4. Unfortunately, during the installation phase of the library item, something crashes and the installation won’t proceed until you tell it to ignore or report the error.
      5. Despite the crash, everything works as expected and you will find the topic installed in your help library:

Here it is, nice and easy. Hope it works for you too.

SSMS is now High-DPI ready

One of the most popular posts on this bog describes how to enable bitmap scaling is SSMS on high DPI displays, which is a sign that more and more people are starting to use 4K displays and are unhappy with SSMS’s behaviour at high DPI. The solution described in that post is to enable bitmap scaling, which renders graphic objects correctly, at the price of some blurriness.

The good news is that starting with SSMS 16.3 high DPI displays are finally first class citizens and SSMS does its best to scale objects properly. By default, SSMS will keep using bitmap scaling: in order to enable DPI scaling you will have to use a manifest file.

  1. Merge this key to your registry:
Windows Registry Editor Version 5.00[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\SideBySide]
  1. Save this manifest file to “C:\Program Files (x86)\Microsoft SQL Server\130\Tools\Binn\ManagementStudio\Ssms.exe.manifest” using UTF-8 format:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0" xmlns:asmv3="urn:schemas-microsoft-com:asm.v3">
        <asmv3:windowsSettings xmlns="">
            <assemblyIdentity type="win32" name="Microsoft.Windows.Common-Controls" version="" processorArchitecture="X86" publicKeyToken="6595b64144ccf1df" language="*" />
            <assemblyIdentity type="win32" name="debuggerproxy.dll" processorArchitecture="X86" version=""></assemblyIdentity>

This is a huge improvement over the bitmap scaling solution we had to use up to now: no more blurriness and proper fonts are used in SSMS.

For comparison, this is how bitmap scaling renders in SSMS 2014:


And this is how DPI scaling renders is SSMS 16.3, with scaling set to 200%:


As you can see, it’s not perfect yet (for instance, I had to change the grid font size to 9pt. in order to have readable fonts).

However, the GUI is much more readable now. For instance, look at the difference in object explorer: (click on the image to open fullsize and see the difference)


Now that your favourite tool is working in high DPI displays, nothing is holding you back from buying one of those fancy 4K laptops!

Upcoming Speaking Engagements

The next few months will be crazy for me. I will be travelling a lot around Europe, speaking about SQL Server topics.

Here is where you will find me in the upcoming weeks:

SQLNexus is a new conference in Copenhagen and will be the official launch event in Denmark for SQL Server 2016.
I will speak about “Responding to Extended Events in near Real-Time”.

SQLBits doesn’t need to be introduced. It’s the biggest SQL Server event in Europe and it will also be the official SQL Server 2016 launch event in UK.
Again, I will speak about “Responding to Extended Events in near Real-Time”.

NTK is a famous conference in Slovenia, which has been running for many years now. This year it will be held in Portorosz, near the Italian border.
It’s going to be fun: I will speak about “Benchmarking, Baselining and Workload Analysis”.

INSIDE-SQL is also a new event, run this year for the first time. It’s an event focused on in-depth concepts, delivered in 75 minutes sessions, with long breaks between sessions, so that attendees can go to the next session without rushing and can hang out with the speakers and ask questions.
I will deliver two sessions:
“Responding to Extended Events in near Real-Time”
“Advanced T-SQL Techniques”

Free SQL Server training from the 40th floor of the Tour Montparnasse in Paris.What else can I say?
I will be speaking about “New Security Features in SQL Server 2016”

One of the coolest SQLSats around!
This time I’ll be speaking about “SQL Server Infernals”, AKA “how to torture your SQL Server instances to death with worst practices”. It’s going to be fun!

I hope to see you at these super cool events!

An annoying Bug in the Restore Dialog

Today, thanks to a customer, I discovered  one of those annoying little things that can really drive you nuts.

Basically, they were trying to restore a backup using the SSMS Restore Database window and they kept getting “No backupset selected to be restored” whenever a backup file was selected.

You just had to select a file for restore and click OK…


… to be met with an error message in the Restore Database window:


The weird thing about it is that the backup file restored perfectly fine from a T-SQL script:


So it had to be something wrong with SSMS, but what?

Looking closer at the restore script, one thing stands out. Look at the file name:


Yep, there’s a leading whitespace in the file name. Could that be the source of the problem?

Let’s try again with the GUI in a slightly different way. This time I will copy the folder path from the “Backup File Location” textbox…


… and paste it directly in the “File name” textbox, right before the file name:


This time everything works as expected.

Bottom line:

  1. This is a bug in SSMS: go on and vote this Connect item to have it fixed in a future version.
  2. Don’t use the GUI to restore a database.
  3. Don’t use the GUI at all.

SSMS in High-DPI Displays: How to Stop the Madness

I spent the last few weeks travelling a lot compared to my usual routine and I got quickly fed up with bringing my mobile workstation with me. My Dell precision M4600 is a powerhouse, but it’s definitely too big and too heavy for travelling, so I decided it was time to buy a small laptop just for travelling and presenting at SQL Saturdays and events around Europe.

After lots of research, I pulled the trigger on a new XPS13. It’s a very nice, tiny and light machine, beefy enough to run my virtual machines and slim enough to fit in a small bag.

So, everything fine? Not quite. The XPS13 2015 sports a stunning QHD touch display, with almost no bezel: a small wonder. The only complaint with it is windows and its (in)ability to scale applications when running at High DPI.

Windows got better at scaling applications on HiDPI displays and Windows 10 is doing a remarkably good job at scaling applications that can actually scale. I am running at maximum resolution (3200 x 1800) with 200% scale factor and, for instance, Visual Studio 2015 renders perfectly:


Other applications scale horribly. For instance, SSMS (SQL Server Management Studio) 2014 is a complete disaster:


At a first glance, it looks ok, but look at those icons on the Object Explorer tree: aren’t they a little bit too small compared to the labels next to them?

I can live with small icons, but you just need to open some dialog windows to understand how bad things really are:


As you can see, text gets scaled correctly, but the size of the window and some controls are completely wrong.

While some dialog windows are easily fixed by resizing them, some other are completely unusable. For instance, the restore database dialog, when locating a backup file, looks like this:


I’m not the first one to discover this kind of issues: Scott Hanselman posted his impressions quite a long time ago, but he offered no solution.

There’s also a Connect item that describes this issue, but… ok, you know what I’m about to say.

A new hope from an old technique

In Windows Vista, you had two possible ways of scaling applications: with the first one (the default) applications were instructed to scale their objects using the scaling factor imposed by the operating system. The results, depending on the quality of the application and the Windows version, could vary a lot. Some scaled correctly, some other look very similar to what we are seeing in SSMS, with some weird-looking GUIs. In Vista, this option was called “XP style DPI scaling”.

The second option, which you could activate by unchecking the “XP style” checkbox, involved drawing the graphical components of the GUI to an off-screen buffer and then drawing them back to the display, scaling the whole thing up to the screen resolution. This option is called “bitmap scaling” and the result is a perfectly laid out GUI:


In order to enable this option in Windows 10, you need to merge this key to your registry:

Windows Registry Editor Version 5.00


Then, the application has to be decorated with a manifest file that instructs Windows to disable DPI scaling and enable bitmap scaling, by declaring the application as DPI unaware. The manifest file has to be saved in the same folder as the executable (ssms.exe) and its name must be ssms.exe.manifest. In this case, for SSMS 2014, the file path is “C:\Program Files (x86)\Microsoft SQL Server\120\Tools\Binn\ManagementStudio\Ssms.exe.manifest”.

Paste this text inside the manifest file and save it in UTF8 encoding:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>

<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0" xmlns:asmv3="urn:schemas-microsoft-com:asm.v3">

    <assemblyIdentity type="win32" name="Microsoft.Windows.Common-Controls" version="" processorArchitecture="*" publicKeyToken="6595b64144ccf1df" language="*">

    <assemblyIdentity type="win32" name="Microsoft.VC90.CRT" version="9.0.21022.8" processorArchitecture="amd64" publicKeyToken="1fc8b3b9a1e18e3b">

<trustInfo xmlns="urn:schemas-microsoft-com:asm.v3">
      <requestedExecutionLevel level="asInvoker" uiAccess="false"/>

  <asmv3:windowsSettings xmlns="">
    <ms_windowsSettings:dpiAware xmlns:ms_windowsSettings="">false</ms_windowsSettings:dpiAware>


This “Vista style” bitmap scaling is very similar to what Apple is doing on his Retina displays, except that Apple uses a different font rendering algorithm that looks better when scaled up. If you use this technique in Windows, ClearType rendering is performed on the off-screen buffer before upscaling, so the final result might look a bit blurry.

The amount of blurriness you will see depends on the scale factor you set in the control panel or in the settings app in Windows 10. Needless to say that exact pixel scaling looks better, so prefer 200% over 225% or 250% scale factors, because there is no such thing as “half pixel”.

Seeing is believing:

Bitmap scaling at 200%

Bitmap scaling at 200%

Bitmap scaling at 225%

Bitmap scaling at 225%

Bitmap scaling at 250%

Bitmap scaling at 250%

That’s it: nice and easy. Enjoy your High DPI lifestyle, until Microsoft comes up with a better solution (or a better SSMS).

SQL Server Infernals – Circle 6: Environment Pollutors


Don’t tell me that you didn’t see it coming: at some point, Developers end up being put to hell by a DBA!

I don’t want to enter the DBA/Developer wars, but some sins committed by Developers really deserve a ticket to the SQL Server hell. In particular, some of those sins are perpetrated when not even a single line of code is written yet and they have to do with the way the development environment is set up.

What they say in Heaven

Before starting a software project, the angelic developers set up their environment in the best of all ways, with proper environment isolation and definition. In particular they will have:

  • Development Environment: this is the place (ideally a dev’s desktop) where the development work is performed. It should resemble the production environment as much as possible.
  • Test Environment (QA): This is where the testers ensure the quality of the application, open bugs and review bug fixes. It should be identical to the production environment (in Heaven it is).
  • User Acceptance Test Environment (UAT): this is where the clients test the quality of third-party applications, request features and file bugs.
  • Staging Environment (Pre-Production): this environment is used to assemble, test and review newer versions of the database before it is moved into production. The hardware mirrors that of the production environment.
  • Production Environment: This is where the real database lives. It can be updated from the staging environment, when available, as well as new functionality and bug fixes release from UAT or staging environment.

If your organization or the project are small, you probably don’t need all of these environments. In Heaven, where time and money are not a constraint, they have all of them and they’re all identical to production. Heh, Heaven is Heaven after all…

Environmental sinners will face SQL Server’s judgement

Setting up your development environment in the wrong way can harm SQL Server (and your software) in many ways, right from the start of the project, throughout its whole lifetime. Let’s see some of the most common sins:


A notable example of Polluted Database

  1. Using the production environment for development: frankly, I don’t think this sin needs any further explanation. On the other hand, don’t assume that nobody’s doing it, despite we’re in 2015: lots of damned developers’ souls confess this sin while entering the SQL Server hell!
  1. Using the test environment for development: Again, this seems so obvious that there should be no need to discuss it: development is development and test is test. The test environment(s) should be used to test the application, not to see it breaking every minute because you changed something. Developing the code and testing it are two different things and, even if you happen to be in charge of both, this is not a good reason to confuse the two tasks.
  1. Using a shared instance for development: Back in the old days, when I was working as an ASP classic developer in a software house, we had a shared development environment on a central IIS server, where everyone saved their code on a shared folder and just had to hit F5 in Internet Explorer to see the changes immediately in action.
    If you think this model is foolish you’re 100% right, but in the 90s’ we didn’t know better. However, while everyone today agrees that it’s a terrible idea for code, you will still find hordes of developers not completely convinced that it’s an equally terrible idea as far as the database is concerned. Having a shared development database greatly simplifies the process of creating a consistent development database, which is a problem only if you have no authoritative source to build it from (which brings us to the next sin).
  1. No source control: Nobody in their right mind would start a software project today without using source control, yet source control for the database is still an esoteric topic, despite the plethora of tools to accomplish this task.
  1. Granting sysadmin rights to the application: If you’re using a local development instance (and you should), you probably are the administrator of that instance. Hey, nothing wrong with that, unless you use windows authentication in your application. In that case, whenever you debug the application in Visual Studio (or whatever you’re using), the application impersonates you (a sysadmin) when hitting the database, so there is no need to grant any permission in order to let the app perform anything on the instance.
    So, what happens when you’re done with development and you have to deploy in test (or, worse, production)? Exactly: nothing works, because (hopefully) the application won’t run with sysadmin privileges in production. At that point, extracting the complete lists of permissions needed by the application is an overwhelming task that you could have happily avoided by developing with a non-privileged user in the first place. When using a regular user, each time the application needs additional permissions, you simply have to add a GRANT statement to the deployment script, which also acts as the documentation the DBA will ask for.
    If you fail to provide this documentation, two things could happen: a) the DBA may refuse to deploy the database b) you could end up needing sysadmin privileges, which means a dedicated instance, which could in turn bring us back to a).
  1. Developing on a different version/edition from production: if your application is targeting SQL Server 2008 R2, developing on SQL Server 2012 could mean that you will discover incompatible T-SQL features after development. The same can be said for the SQL Server edition: if you are using a Developer Edition for development but you are targeting Standard Edition, you will discover the use of enterprise-only features when it’s too late. You can save yourself all the pain by using in development the same exact SQL Server version and edition you are targeting in production.

In the next episodes of SQL Server Infernals I’m afraid I will have to put more developers to hell. If you’re a developer, stay tuned to find out if your soul is a at risk! If you’re a DBA, stay tuned to enjoy seeing more developers damned!

SQL Server Infernals – Circle 5: Inconsistent Baptists


There’s a place in the SQL Server hell where you can find poor souls wandering the paths of their circle, shouting nonsense table names or system-generated constraint names, trying to baptize everything they find on their way in a different manner. They might seem innocuous at a first glance, but beware those damned souls, as they can raise confusion and endanger performance.

What they say in Heaven

Guided by the Intelligent Designer’s hands, database architects in Heaven always name their tables, columns and all database objects following the rules in the ISO 11179 standard. However, standards aside, the most important thing they do is adhere to a single naming convention, so that every angelic DBA and developer can sing in the same language.

It has to be said that even in Heaven some angels prefer specific naming conventions and some other angels might prefer different ones (say plural or singular table names), but as soon as they start to design a database, every disagreement magically disappears and they all sing in harmony.

Damnation by namification

Some naming conventions are better than others, but many times it all comes down to personal preference. It’s a highly debatable subject and I will refrain from posting here what my preference is. If you want to learn more about naming conventions, take advice from one of the masters.

That said, some naming conventions are really bad and adopting them is a one way ticket to the SQL Server hell:


  1. Hungarian Notation: my friends in Hungary will forgive me if I say that their notation doesn’t play well with database objects. In fact, the Hungarian Notation was conceived in order to overcome the lack of proper data types in the BCPL language, putting a metadata prefix in each variable name. For instance, a variable holding a string would carry the “str” prefix, while a variable holding a long integer would carry the “l” prefix.
    SQL Server (and all modern relational databases) have proper data type support and all sorts of metadata discovery features, so there is no point in naming a table “tbl_customer” or a view “vwSales”. Moreover, if the DBA decides to break a table in two and expose its previous structure as a view (in order to prevent breaking existing code), having the “tbl” prefix in the view name completely defeats the purpose of identifying the object type by its prefix.
    Next time you’re tempted to use the Hungarian Notation ask yourself: “is my name John or DBA_John?”


    Hungary is a nice str_country.

  2. Using insanely short object names: Some legacy databases (yes, you, DB2/400) used to have a hard maximum of 10 characters for object names. It wasn’t uncommon to see table names such as “VN30SKF0OF” or “PRB10SPE4F”: good luck figuring out what those tables represented!
    Fortunately, those days are gone and today there is no single reason to use alphabet soup names for your objects. The object name is a contract between the object and its contents and it should be immediately clear what the contents are by just glancing at the name.
  1. Using insanely long object names: On the other hand, table names such as “ThisIsTheViewThatContainsOrdersWhichAreYetToBeShipped” adds nothing to clarity of the schema. “UnshippedOrders” will do just as well.
  1. Mixing Languages: if you’re fortunate enough to be a native English speaker, you have no idea what this means. In countries such as Italy or Spain, this is a real issue. Many people may end up designing different parts the database schema and each designer may be inclined to use English (the lingua franca of Information Technology) or his/her first language. Needless to say that the result is a mess.
  1. Using the “sp_” prefix for stored procedures: it’s a special case of Hungarian Notation, with severe performance implications. In his blog, Aaron Bertrand discussed the notorious negative impact of the “sp_” prefix, offering a performance comparison with charts and crunchy numbers.
    TL;DR version: SQL Server looks up objects with the sp_ prefix in the master database first, then in the user database. While it may look like a negligible performance issue, it can explode at scale.
  1. Using reserved keywords or illegal characters: While it’s still possible to include almost anything inside square brackets, the use of spaces, quotes or any other illegal character is a totally unneeded masochistic habit. Reserved keywords may also add a thrilling touch of insane confusion to your T-SQL code:
    Enough said.
  1. Using system-generated names for constraints, indexes and so on: When you don’t name your constraints and indexes explicitly, SQL Server is kind enough as to do it for you, using a semi-random system-generated name. That’s great! Uh, wait a moment: this means that two databases deployed to two different instances will contains the same index with a different name, making all your deployment scripts nearly useless. Do yourself a favor and take the time to name all your objects explicitly.
  1. No naming convention or multiple, inconsistent naming conventions: The worst of all mistakes is having multiple naming conventions, or no naming convention at all (which is equal to “as many naming conventions as objects in the database”). Naming conventions is a sort of religious subject and there are multiple valid reasons to adopt one or another: the only thing you should absolutely avoid is turning your database into a sort of Babel tower, where multiple different languages are spoken and nobody understands what the others say.


This is the last circle of SQL Server hell dedicated to Database Design sins: in the next episode of SQL Server Infernals we will venture into the first circle dedicated to development. Stay tuned!

SQL Server Infernals – Circle 4: Anarchic Designers


Constraints are sometimes annoying in real life, but no society can exist without rules and regulations. The same concept is found in Database Design: no good data can exist without constraints.

What they say in Heaven

Constraints define what is acceptable in the database and what does not comply with business rules. In Heaven, where the perfect database runs smoothly, no constraint is overlooked and all the data obeys to the rules of angels:

  • Every column accepts only the data it was meant for, using the appropriate data type
  • Every column that requires a value has a NOT NULL constraint
  • Every column that references a key in a different table has a FOREIGN KEY constraint
  • Every column that must comply with a business rule has a CHECK constraint
  • Every column that must be populated with a predefined value has a DEFAULT constraint
  • Every table has a PRIMARY KEY constraint
  • Every group of columns that does not accept duplicate values has a UNIQUE constraint

Chaos belongs to hell

OK: Heaven is Heaven, but what about hell? Let’s see what will get you instant damnation:


  1. Using the wrong data type: we already found out that the SQL Server hell is full of Shaky Typers. The data type is the first constraint on your data: choose it carefully.
  1. No PRIMARY KEY constraints: In the relational model, tables have primary keys. Without a primary key, a table is not even a table (exception made for staging tables and other temporary objects). Do you want duplicate data and unusable data? Go on and drop your primary key.
  1. NULL and NOT NULL used interchangeably: NOT NULL is a constraint on your data: failing to mark required columns with NOT NULL will inevitably mean that you’ll end up having missing information in your rows. At the same time, marking all columns as NOT NULL will bring garbage data in the database, because users will start using dummy data to circumvent the stupid constraint. We already met these sinners in the First Circle of the SQL Server hell.
  1. No Foreign Key constraints: Foreign Keys can be annoying, because they force you to modify the database in the correct order, but following the rules pays off. Without proper constraints, what would happen if you tried to delete from a lookup table a key referenced in other tables? Unfortunately, it would work, silently destroying the correctness of your data.
    What would happen if you tried to sneak in a row that references a non-existing key? Again, it would bring in invalid data.
  1. No CHECK constraints: Many columns have explicit or implicit constraints: failing to add them to the database schema means that values forbidden by the business rules will start to flow into the database. Some constraints are implicit, but equally important as the explicit ones. For instance:
    • an order should never be placed in a future date
    • a stock quantity should never be negative
    • a ZIP code should only contain numeric characters
    • a Social Security Number should be exactly 9 digits long
  1. Relying on the application to validate data: If I had €0.01 for every time I found invalid data in a database and the developers said “the application will guarantee consistency”, I would be blogging from my castle in Mauritius. Maybe the application can guarantee consistency for the data that it manipulates (and it won’t, trust me), but it can do nothing for other applications using the same database. Often the database is a hub for many applications, each with its own degree of complexity and each with its level of quality. Pretending that all these applications will independently guarantee that no invalid data is brought in is totally unrealistic.

 The last circle of SQL Server hell dedicated to Database Design sins is the circle of Inconsistent Baptists, those who fail to comply to sensible naming conventions. Stay tuned!

SQL Server Infernals – Circle 3: Shaky Typers


Choosing the right data type for your columns is first of all a design decision that has tremendous impact on the correctness of the database schema. It is not just about performance or space usage: the data type is the first constraint on your data and it decides what can be persisted in your columns and what is not acceptable.

Choosing the wrong data type for your columns is a mistake that might make your life as a DBA look like hell.

What they say in Heaven

Guided by angelic spells, the hands that design databases in Heaven always choose the right data type. Database architects always look at the logical schema and ask the right questions about each attribute and they always manage to understand what the attribute is used for and what it will be used for in the future.

What will put you to hell

Choosing the wrong data type is like trying to fit a square peg in a round hole. The worst thing about it is that you end up damaging the peg… ahem… the data.


  1. Using numeric data types for non-numeric attributes: Even if a telephone number contains only digits and it’s called telephone number, it is not a number at all. It does not allow mathematical operations and it has no order relation (saying that a telephone number is greater than another one makes no sense). In fact, a telephone number is a code you have to dial to contact a telephone extension. The same can be said for ZIP codes, which only allow numeric digits, but are nothing like a number. Storing this data in a numeric column is looking for trouble.
  1. Storing data as their human-readable representation: A Notable example is dates stored as (var)char. The string representation of a date is not a date at all: without the validation rules included in the date types, any invalid date could be saved in your column, including ‘2015-02-30’ or ‘2015-33-99’. Moreover, varchar columns do not allow date manipulation functions, such as DATEADD, DATEDIFF, YEAR, MONTH and so on. Another reason why this is a terrible idea is that dates have their own sorting rules, which you lose when you store them as strings. You also need more storage space to save a string representation of a date compared to the proper date type. If you really want to convert a date to a string, you can find many algorithms and functions to perform the conversion in this article I wrote for SQLServerCentral in 2012, but please do it in your presentation layer, not when storing the data in your tables.
    Another surprisingly common mistake in the AS/400 world is storing dates in three separate integer columns for year, month and day. I have no idea where this pattern comes from, but it definitely belongs to hell.
    While much more uncommon in the wild, the same applies to numbers: storing them as varchars is a terrible idea.
    Extra evil bonus: you get double evil points for storing dates and numbers as nvarchar: double the storage, double the pain.
  1. Using deprecated data types: (n)text and image are things of the past: get over it. The replacement (n)varchar(max) and varbinary(max) are much more powerful and flexible.
  1. Using “extended” data type just to “be safe”: This applies both to numeric and character columns: using a bigger data type just to play it safe can be a good idea at times, but not when the size of the column is well known upfront and is instead a vital constraint on the data itself. For instance, a ZIP code longer than 5 characters is obviously an error. A social security number longer than 9 digits is not valid.
    Along the same lines, storing years in a int column is only going to be a waste of storage space. The same can be said about small lookup tables with just a handful of rows in them, where the key column can be a smallint or even a tinyint: it won’t save much space in the lookup table itself, but it can save lots of space in the main tables (with many more rows) where the code is referenced.
  1. Storing fixed-size information in varchar columns: Similarly to the previous sin, when your attribute has a fixed character size, there is no point in using a varying character type. If your attribute has exactly 3 characters, why use varchar(3)?
    Extra evil bonus: varchar(1) will get you double points.
  1. Storing duration in time or datetime columns: Datetime and time represent points in time and they are not meant for storing durations. If you really want to store a duration, use a numeric column to store the number of seconds (it’s the ANSI standard unit measure for representing a duration). Even better, you could store the start/end date and time in two separate datetime columns. SQL Server 2016 also supports periods. 
  1. Getting Unicode wrong: Choosing nvarchar for attributes that will never contain Unicode data and choosing varchar for attributes that can contain Unicode data are equally evil and will get you instant damnation. For instance, a ZIP code will only contain numeric characters, so using Unicode data types will have the only outcome of wasting space. At the same time, storing customer business names or annotations in varchar columns means that you won’t be able to persist international characters. While it may appear quite unlikely that such characters will ever appear in your database, you will regret your decision when that happens (and it will). 
  1. Messing with XML: I’m not a big fan of XML in the database, but sometimes it can come handy. Storing XML data in a plain varchar column is a very bad idea. The XML data type provides validation rules that won’t allow in invalid or malformed XML and also provides functions to manipulate the XML data. Storing schema-less XML is another bad idea: if you have an XML schema use it, otherwise you will end up saving invalid data. On the other hand, using XML to go “beyond relational” and mimic Oracle’s nested tables will only get you damned. Fun times. 
  1. Using different data types in different tables for the same attribute: there’s only one thing worse than getting your data types wrong: getting them wrong in multiple places. Once you decided the data type to store an attribute, don’t change your mind when designing new tables. If it is a varchar(10), don’t use varchar(15) in your next table. Usually proper foreign key constraints help you avoid this issue, but it’s not always the case.
    If this query returns rows, chances are that you have schizophrenic columns in your database schema:

    WITH my_schema AS (
        SELECT OBJECT_NAME(c.object_id) AS table_name,
   AS column_name,
   AS type_name,
        FROM sys.columns AS c
        INNER JOIN sys.types AS t
            ON c.system_type_id = t.system_type_id
    incarnations AS (
        SELECT *,
            DENSE_RANK() OVER (
                PARTITION BY column_name
                ORDER BY type_name, max_length, precision, scale
            ) AS incarnation_number
        FROM my_schema
    incarnation_count AS (
        SELECT *,
            MAX(incarnation_number) OVER (
                PARTITION BY column_name
            ) AS incarnation_count
        FROM incarnations
    SELECT *
    FROM incarnation_count
    WHERE incarnation_count > 1
    ORDER BY incarnation_count DESC,

The lack of proper constraints will be the topic of the next post, when we will meet the anarchic designers. Stay tuned!