This file is a harmful and undesirable program. Probably virus. It's recommended to delete it.
What is Mssql.exe Windows startup process
File name: Mssql.exe
Program name: MSSQL
Description: SDBOT TROJAN
Information added by: Elrik at 02 March 2008
Hint: If mssql.exe file is a virus or trojan, we recommend to use a antivirus software or registry cleaner.
We are presenting list of Windows processes, startup files.
Name of Mssql.exe is MSSQL. Some of them are viruses, so you should use a antivirus program.