What is SYSNAME data type in SQL Server?

sysname is a built in datatype limited to 128 Unicode characters that, IIRC, is used primarily to store object names when creating scripts. Its value cannot be NULL

It is basically the same as using nvarchar(128) NOT NULL

EDIT

As mentioned by @Jim in the comments, I don't think there is really a business case where you would use sysname to be honest. It is mainly used by Microsoft when building the internal sys tables and stored procedures etc within SQL Server.

For example, by executing Exec sp_help 'sys.tables' you will see that the column name is defined as sysname this is because the value of this is actually an object in itself (a table)

I wouldn't worry too much about it.

It's also worth noting that for those people still using SQL Server 6.5 and lower (are there still people using it?) the built in type of sysname is the equivalent of varchar(30)

Documentation

sysname is defined with the documentation for nchar and nvarchar, in the remarks section:

sysname is a system-supplied user-defined data type that is functionally equivalent to nvarchar(128), except that it is not nullable. sysname is used to reference database object names.

To clarify the above remarks, by default sysname is defined as NOT NULL it is certainly possible to define it as nullable. It is also important to note that the exact definition can vary between instances of SQL Server.

Using Special Data Types

The sysname data type is used for table columns, variables, and storedprocedure parameters that store object names. The exact definition ofsysname is related to the rules for identifiers. Therefore, it canvary between instances of SQL Server. sysname is functionally the sameas nvarchar(128) except that, by default, sysname is NOT NULL. Inearlier versions of SQL Server, sysname is defined as varchar(30).

Some further information about sysname allowing or disallowing NULL values can be found here https://stackoverflow.com/a/52290792/300863

Just because it is the default (to be NOT NULL) does not guarantee that it will be!

Is there use case you can provide?

If you ever have the need for creating some dynamic sql it is appropriate to use sysname as data type for variables holding table names, column names and server names.

Just as an FYI....

select * from sys.types where system_type_id = 231 gives you two rows.

(i'm not sure what this means yet but i'm 100% sure it's messing up my code right now)

edit: i guess what it means is that you should join by the user_type_id in this situation (my situation) or possibly both the user_type_id and the system_type_id

name        system_type_id   user_type_id   schema_id   principal_id    max_length  precision   scale   collation_name                  is_nullable     is_user_defined     is_assembly_type    default_object_id   rule_object_idnvarchar    231              231            4           NULL            8000        0           0       SQL_Latin1_General_CP1_CI_AS    1               0                   0                   0                   0sysname     231              256            4           NULL            256         0           0       SQL_Latin1_General_CP1_CI_AS    0               0                   0                   0                   0

create procedure dbo.yyy_test (    @col_one    nvarchar(max),    @col_two    nvarchar(max)  = 'default',    @col_three  nvarchar(1),    @col_four   nvarchar(1)    = 'default',    @col_five   nvarchar(128),    @col_six    nvarchar(128)  = 'default',    @col_seven  sysname  )as begin     select 1end 

This query:

select  parm.name AS Parameter,            parm.max_length,         parm.parameter_id          from    sys.procedures sp        join sys.parameters parm ON sp.object_id = parm.object_id         where   sp.name = 'yyy_test'order   by parm.parameter_id

Yields:

parameter           max_length  parameter_id@col_one            -1          1@col_two            -1          2@col_three           2          3@col_four            2          4@col_five            256        5@col_six             256        6@col_seven           256        7

And This:

select  parm.name as parameter,            parm.max_length,         parm.parameter_id,        typ.name as data_type,         typ.system_type_id,         typ.user_type_id,        typ.collation_name,        typ.is_nullable from    sys.procedures sp        join sys.parameters parm ON sp.object_id = parm.object_id                join sys.types typ ON parm.system_type_id = typ.system_type_id        where   sp.name = 'yyy_test'order   by parm.parameter_id

Gives You This:

parameter   max_length  parameter_id    data_type   system_type_id  user_type_id    collation_name                  is_nullable@col_one    -1          1               nvarchar    231             231             SQL_Latin1_General_CP1_CI_AS    1@col_one    -1          1               sysname     231             256             SQL_Latin1_General_CP1_CI_AS    0@col_two    -1          2               nvarchar    231             231             SQL_Latin1_General_CP1_CI_AS    1@col_two    -1          2               sysname     231             256             SQL_Latin1_General_CP1_CI_AS    0@col_three   2          3               nvarchar    231             231             SQL_Latin1_General_CP1_CI_AS    1@col_three   2          3               sysname     231             256             SQL_Latin1_General_CP1_CI_AS    0@col_four    2          4               nvarchar    231             231             SQL_Latin1_General_CP1_CI_AS    1@col_four    2          4               sysname     231             256             SQL_Latin1_General_CP1_CI_AS    0@col_five    256        5               nvarchar    231             231             SQL_Latin1_General_CP1_CI_AS    1@col_five    256        5               sysname     231             256             SQL_Latin1_General_CP1_CI_AS    0@col_six     256        6               nvarchar    231             231             SQL_Latin1_General_CP1_CI_AS    1@col_six     256        6               sysname     231             256             SQL_Latin1_General_CP1_CI_AS    0@col_seven   256        7               nvarchar    231             231             SQL_Latin1_General_CP1_CI_AS    1@col_seven   256        7               sysname     231             256             SQL_Latin1_General_CP1_CI_AS    0