Chapter 2: Transact-SQL Functions

suser_name

Returns the name of the current server user or the user whose server ID is specified.

suser_name([server_user_id])

select suser_name()

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sa

select suser_name(4)

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margaret

suser_name, a system function, returns the server user’s name. Server user IDs are stored in syslogins. If no server_user_id is supplied, suser_name returns the name of the current user.
For general information about system functions, see “System functions”.

ANSI SQL – Compliance level: Transact-SQL extension.

Any user can execute suser_name.