Sql is a file extension of Structured Query Language. It is a Database interrogation system that can be opened with Apachi.
If you have a Sql extension file on your computer it might be database backup of a webpage. It can be opened by Notepad and you are able to read it in some way. However if you want to see whole structure of table you should have a Apache system that installed Mysql. Then you should write http://localhost/Phpmyadmin/ into it. Finally you can install the file with import command.
You can check internet to find a free software that can open Database.
What to use SQL
which page related to SQL file
SQL Related Searches
You can check related links about SQL fileextension.