For the concepts of relational algebra that underly SQL, here is an overview:
https://en.wikipedia.org/wiki/Relational_algebra
The mathematical operators and functions included in the T-SQL language are quite basic.
https://msdn.microsoft.com/en-us/library/ms187716.aspx
https://msdn.microsoft.com/en-us/library/ms177516.aspx
"Do not seek to follow in the footsteps of the wise. Instead, seek what they sought." - Matsuo Basho