The sysname datatype defaults to not NULL.


August 26, 2021 by Kenneth Fisher

The other day I was creating a table to store some metadata. Since the metadata I was collecting ( for example) uses the datatype sysname I used the same datatype. In case you didn’t know sysname is an nvarchar(128) user defined datatype used in a number of the system views.

Anyway, I was a bit surprised (and later realized I probably shouldn’t be) that the default for sysname is to not allow nulls.

CREATE TABLE sysname_test (
	Col1 sysname
	,Col2 nvarchar(128)
EXEC sp_help sysname_test;
DROP TABLE sysname_test;

Now you can override that if you need to, it’s just the default, but the final definition for sysname is going to be:

sysname := nvarchar(128) NOT NULL

Which you can see pretty easily by looking in the sys.types system view.

SELECT * FROM sys.types
WHERE NAME = 'sysname';

4 thoughts on “The sysname datatype defaults to not NULL.

  1. Chad Estes says:

    You’ve piqued my interest; why would you need/want a nullable field of the sysname type? I would think you’d only use this for table, index, column, etc. names, so I’d be curious to know why any of these values would be null.

    • In this case I’m saving a bunch of metadata and occasionally I’ll have a row that’s missing a piece of information. I’d be surprised to see a nullable sysname in a system view, but when I’m using it in my own code it happens occasionally :).

  2. […] Kenneth Fisher discovers a secret of the sysname datatype: […]

  3. […] because that’s usually plenty. You might need more (or even less) or you could even use sysname. I typically use original_login() because it ignores impersonation. However, depending on how your […]

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