How to upload .dat file to the SQL Server database?

The best and the safest way to do this to first save the .dat as .txt and then upload to Microsoft Access and Upload the Access File as shown Here

To upload for .dat to Access

1.  make .dat as .txt.
2. open Microsoft Access
3. create a new blank database
4. go to EXTERNAL DATA tab
5. select TEXT
6. follow the pop up wizzard
7. Enter the delimited format generally '|'
8. Change all the data type to TEXT to avoid errors in uploading the data
9. click next next and finish. 
10. Save the table in .mdb format and upload it to the database as Access file