how to connect to mssql in unity for hololesn (Build Setting Error)

For connecting to mssql in unity, I referred to

System.Data.dll, located in C:\Program Files\Unity\Editor\Data\Mono\lib\mono\unity

( I found some blogs to recommend it, since unity can only refer to mono libraries)

It was successfully operated in unity editor.

However, when I did Bulid Setting for Hololens by Windows Universial Platform,

error occured to warn that it could not find System.dll and mscorlib.dll.

In my guess, it occured,

becuase the version of C:\Program Files\Unity\Editor\Data\Mono\lib\mono\unity\System.Data.dll

is 2.0, which is lower than the curretly defalut version of unity C# script 4.6.

I cannot find how to solve that problem. Please, help me by giving some good advice.

Thank you.