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Category: Data Types

Data Type Casing in SQL Server

Aaron Bertrand finds a case where casing matters:

We all have coding conventions that we have learned and adopted over the years and, trust me, we can be stubborn about them once they’re part of our muscle memory. For a long time, I would always uppercase data type names, like INTVARCHAR, and DATETIME. Then I came across a scenario where this wasn’t possible anymore: a case-sensitive instance. In a recent post, Solomon Rutzky suggested:

As long as you are working with SQL Server 2008 or newer, all data type names, including sysname, are always case-insensitive, regardless of instance-level or database-level collations.

I have a counter-example that has led me to be much more careful about always matching the case found in sys.types.

Click through for that scenario.

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Implicit Conversions and SARGability

Erik Darling bears bad news:

Data types are one of those core things you need to get right. Whether it’s matching types between join columns, or between parameters and predicates, not doing so can really squash application performance in quite similar ways to writing non-SARGable predicates.

That’s because — wait for it — a lot of the stuff we’ve talked about over the last week that can happen with poorly written predicates can happen with poorly matched data types, too.

Click through for an example. If this keeps up, we may never save Sarge.

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Working with Complex Return Types in Power Query

Gerhard Brueckl works with some complex data:

When working with Power Query, you have probably already realized that every expression you write returns a value of a specific type. Usually this will be a primitive type like text, number, or date. (A full list of types available in Power Query can be found here: https://docs.microsoft.com/en-us/powerquery-m/m-spec-types). If for some reason the type of an expression cannot be defined, the special type *any* will be used. For sure you already encountered this when using Table.AddColumn which, by default, results in the new column being of type *any*.

Read on to learn more, including what you can do if you’re creating Power Query functions.

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Avoid Deprecated Data Types

Aaron Bertrand has some advice for us:

I’ve recently discussed a few features that Microsoft advises against using, and that I think you should forget exist, too. There was the case where a colleague constantly promoted the deprecated backward compatibility view sys.sysprocesses instead of newer dynamic management views (DMVs), and another case where a different colleague took down a production server using SQL Server Profiler.

My latest run-in with things best forgotten is a new stored procedure with an ntext parameter. I checked and, sure enough, the data type matches the schema for the underlying table. My mind started racing about these older data types to explain why we really shouldn’t be using them anymore:

I can’t remember the last time I saw new SQL Server tables created with ntext or other deprecated types, but apparently it happens.

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Data Type Conversions and Query Folding

Chris Webb explains how data type conversions and query folding might not mix:

It’s surprisingly easy to stop query folding happening in Power Query by changing the data type of a column. This is mentioned in the docs here, and it’s something several people have blogged about already (for example here). However there is something new to note: an option that will allow you to convert text columns to number or date columns in a foldable way for SQL Server data sources.

Consider the following table in a SQL Server database that consists of a single nvarchar(50) column containing numeric values:

Click through for the example, and also check out the comments below for more info.

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Storing DATETIMEOFFSETs

Randolph West shows us how the DATETIMEOFFSET type is stored in SQL Server:

Cast your mind back to our discussion on DATETIME2. As you know, DATETIME2 is basically the same as squishing DATE (3 bytes) and TIME (between 3 and 5 bytes depending on the scale) into the same column. You end up with a persisted value that is between 6 and 8 bytes wide.

DATETIMEOFFSET is kinda sorta the same thing, but with more bytes on the end. If you take a look at the Microsoft Docs page, the similar idea of a varied column size is retained. For a scale of 0 fractions of a second you only need 8 bytes to store your value, while the default scale of 7 decimal places for storing seconds requires the full 10 bytes.

Click through to understand how the sordid details.

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Memory Grants for CHAR vs VARCHAR

Erik Darling has a head-slapping moment:

While working with a client recently, we found that someone, at some point in time, probably during the original migration from Access, had chosen CHAR columns rather than VARCHAR columns.

Okay, fine. How bad could it be?

Bad enough that… A whole bunch of columns that only had a single character in them were stored in CHAR(1000) columns.

I like CHAR…well, to be specific, NCHAR. But only when you’ll need exactly that many characters.

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Arithmetic Operations on DATETIME Data Types

Eitan Bluman shows off some math skills:

Mathematical addition and subtraction can be performed between two datetime data types:

SET @d2 = '1900-03-30 18:00'SELECT@d1 + @d2 -- result: 1900-04-01 10:15:15.900, @d1 - @d2 -- result: 1899-10-05 22:15:15.900, @d2 - @d1 -- result: 1900-03-29 01:44:44.100

This means that we can have basic datetime arithmetics in SQL server. We can use subtraction to find an accurate difference between two dates, and use addition to add an accurate interval to a datetime column or variable.

This is one of those things you can do, but I’m not very fond of. First of all, as Eitan points out, you can’t do these in the (in all ways superior) DATETIME2 data type. Secondly, it adds some confusion to the code, as you don’t always get what you expect.

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