Category: Data Types

Raul Gonzalez shows how to get one of the benefits of older, deprecated data types using (MAX) data types:

We can see that our table is managed by two different allocation units, IN_ROW_DATA and LOB_DATA, which means that all data within columns of the data types above, will end up in different pages by default, regardless of the size of the data.

This is the default behaviour for old LOB types, to be stored separately, but new LOB types (MAX) by default will try to get them In-Row if they are small enough to fit.

Having some of those documents In-Row will result in a serious increase in the number of pages to scan, therefore affecting performance.

Note that for the table scan we have used only the IN_ROW_DATA pages, making it much lighter than if we have to scan the sum of all pages.

This might be helpful for some situations, like where you rarely need to get to the LOB data.

Erik Darling warns against using SQL_VARIANT data types:

I half-stumbled on the weirdness around SQL_VARIANT a while back while writing another post about implicit conversion. What I didn’t get into at the time is that it can give you incorrect results.

When I see people using SQL_VARIANT, it’s often in dynamic SQL, when they don’t know what someone will pass in, or what they’ll compare it to. One issue with that is you’ll have to enclose most things in single quotes, in case a string or date is passed in. Ever try to hand SQL those without quotes? Bad news bears. You don’t get very far.

Read on for the demo.  I have never used SQL_VARIANT in any project.  I’ve done a lot of crazy things with SQL Server (some of them intentionally) but never this.

Daniel Hutmacher explains what binary data types are and one use case:

Because binary values are essentially strings, they easily convert to and from character strings, using CAST or CONVERT. To convert the binary value of 0x41 to a plain-text character value, try

SELECT CAST(0x41 AS char(1));    --- 'A'

The binary value 0x41 is equivalent to decimal 65, and CHAR(65) is the letter “A”. Note that I haven’t placed any quotes around 0x41 – that’s because it’s a numeric value (albeit in hex notation) and not a string.

A couple use cases I’ve seen are creating hashes (SHA1 or MD5) for change detection, storing password hashes, and encrypted columns—Always Encrypted uses varbinary data types to store encrypted information, for example.

Erik Darling shows how variable definition can be important, even without implicit conversion:

SQL Server makes many good and successful attempts at something called predicate pushdown, or predicate pushing. This is where certain filter conditions are applied directly to the data access operation. It can sometimes prevent reading all the rows in a table, depending on index structure and if you’re searching on an equality vs. a range, or something else.

What it’s really good for is limiting data movement. When rows are filtered at access time, you avoid needing to pass them all to a separate operator in order to reduce them to the rows you’re actually interested in. Fun for you! Be extra cautious of filter operators happening really late in your execution plans.

Click through for Erik’s demo.