Category: Data Types

Dave Saunders describes the concept of linear data structures:

As we said in the introduction, a data structure is ‘linear’ if the elements form a sequence.

That means that the data structure has a first and last element, and each element is connected to its previous and next element.

– An ‘array’ is a linear data structure; the items are stores sequentially.

– A ‘graph’ is not a linear data structure; any node can be linked to any other node in the graph – there is no fixed ‘sequence’.

Click through for several examples of linear data structures.

Steve Jones wants to know if people are still using CHAR:

I ran across an article, titled When to use CHAR, VARCHAR, or VARCHAR(MAX), which struck me as something I never do. I mean, I do use varchar (and nvarchar), but I can’t remember the last time I actually created a char column. The article is worth a read, and it sets the stage for you to think about your database design process and the choices you make.

It’s Friday, and if you take a few minutes and think about the last few times you’ve added columns to a table have you used CHAR as a data type? Or do you default to varchar of any size as a general rule?

Yeah, using CHAR (or NCHAR, which you’d probably want to use instead) is pretty rare. This is a consequence of storage becoming much less of a constraint over the past couple decades, as well as considerable gains in efficiency for data platform products. (N)CHAR might be a little faster than (N)VARCHAR for certain operations and may be a bit more efficient for single-character columns, but I agree with Steve’s premise.

Greg Larsen compares CHAR, VARCHAR, and VARCHAR(MAX):

In every database, there are different kinds of data that need to be stored. Some data is strictly numeric, while other data consists of only letters or a combination of letters, numbers, and even special symbols. Whether it is just stored in memory or on disk, each piece of data requires a data type. Picking the correct data type depends on the characteristics of the data being stored. This article explains the differences between CHAR, VARCHAR, and VARCHAR(MAX).

Click through for Greg’s explanation. My official rule of thumb is as follows:

• If you have a fixed-length code which you display to customers, use NCHAR.
• If you have a fixed-length code which you only use internally and you know that the code will never include characters outside of your SQL Server installation’s code page and you know that the code page will never change…probably still use NCHAR, though if you twist my arm enough I’d say fine, CHAR.
• Otherwise, use NVARCHAR.

Three decades ago, the choice was a lot trickier given performance differences between the two. Today? Unless you’re hunting for microseconds I don’t think you’ll see a practical difference. And if you are hunting for microseconds, you probably want more than rules of thumb.