SUSER_SID (Transact-SQL)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Returns the security identification number (SID) for the specified login name.
Transact-SQL syntax conventions
Syntax
SUSER_SID ( [ 'login' ] [ , Param2 ] )
Arguments
' login '
Applies to: SQL Server 2008 (10.0.x) and later
Is the login name of the user. login is sysname. login, which is optional, can be a SQL Server login or Microsoft Windows user or group. If login is not specified, information about the current security context is returned. If the parameter contains the word NULL will return NULL.
Param2
Applies to: SQL Server 2012 (11.x) and later
Specifies whether the login name is validated. Param2 is of type int and is optional. When Param2 is 0, the login name is not validated. When Param2 is not specified as 0, the Windows login name is verified to be exactly the same as the login name stored in SQL Server.
Return Types
varbinary(85)
Remarks
SUSER_SID can be used as a DEFAULT constraint in either ALTER TABLE or CREATE TABLE. SUSER_SID can be used in a select list, in a WHERE clause, and anywhere an expression is allowed. SUSER_SID must always be followed by parentheses, even if no parameter is specified.
When called without an argument, SUSER_SID returns the SID of the current security context. When called without an argument within a batch that has switched context by using EXECUTE AS, SUSER_SID returns the SID of the impersonated context. When called from an impersonated context, SUSER_SID(ORIGINAL_LOGIN()) returns the SID of the original context.
When the SQL Server collation and the Windows collation are different, SUSER_SID can fail when SQL Server and Windows store the login in a different format. For example, if the Windows computer TestComputer has the login User and SQL Server stores the login as TESTCOMPUTER\User, the lookup of the login TestComputer\User might fail to resolve the login name correctly. To skip this validation of the login name, use Param2. Differing collations is often a cause of SQL Server error 15401:
Windows NT user or group '%s' not found. Check the name again.
Azure SQL Database Remarks
SUSER_SID always return the login SID for the current security context. Use sys.database_principals to obtain the SID of a different login.
The SUSER_SID statement does not support execution using an impersonated security context through EXECUTE AS.
Examples
A. Using SUSER_SID
The following example returns the security identification number (SID) for the current security context.
SELECT SUSER_SID();
B. Using SUSER_SID with a specific login
The following example returns the security identification number for the SQL Server sa login.
Applies to: SQL Server 2012 (11.x) and later
SELECT SUSER_SID('sa');
GO
C. Using SUSER_SID with a Windows user name
The following example returns the security identification number for the Windows user London\Workstation1.
Applies to: SQL Server 2012 (11.x) and later
SELECT SUSER_SID('London\Workstation1');
GO
D. Using SUSER_SID as a DEFAULT constraint
The following example uses SUSER_SID as a DEFAULT constraint in a CREATE TABLE statement.
USE AdventureWorks2022;
GO
CREATE TABLE sid_example
(
login_sid VARBINARY(85) DEFAULT SUSER_SID(),
login_name VARCHAR(30) DEFAULT SYSTEM_USER,
login_dept VARCHAR(10) DEFAULT 'SALES',
login_date DATETIME DEFAULT GETDATE()
);
GO
INSERT sid_example DEFAULT VALUES;
GO
E. Comparing the Windows login name to the login name stored in SQL Server
The following example shows how to use Param2 to obtain the SID from Windows and uses that SID as an input to the SUSER_SNAME function. The example provides the login in the format in which it is stored in Windows (TestComputer\User), and returns the login in the format in which it is stored in SQL Server (TESTCOMPUTER\User).
Applies to: SQL Server 2012 (11.x) and later
SELECT SUSER_SNAME(SUSER_SID('TestComputer\User', 0));
See Also
ORIGINAL_LOGIN (Transact-SQL)
CREATE TABLE (Transact-SQL)
binary and varbinary (Transact-SQL)
System Functions (Transact-SQL)