SYSTEM_USER special register

The SYSTEM_USER special register specifies the authorization ID of the user that connected to the database. The value of this register can only be changed by connecting as a user with a different authorization ID. The data type of the register is VARCHAR(128). If the length of the authorization ID is less than 8 bytes, the special register value is padded with trailing blanks such that the length is 8 bytes.

See "Example" in the description of the SET SESSION AUTHORIZATION statement.