title: How to connect SQL Server Database with Unity3D?
body: <p>My English is not good but I’m trying my best to describe my problems. I have copied  I18N.dll, I18N.CJK.dll, I18N.West.dll and System.Data.dll from  </p>
  
  <p><code>D:\Program Files\Unity\Editor\Data\Mono\lib\mono\2.0</code>,   </p>
  
  <p>but soon an error occurred as follows:  </p>
  
  <blockquote>
    <p>error CS1703: Multiple assemblies with equivalent identity have been imported: 
    'D:\GSS Project\Assets\Plugins\System.Data.dll' and 'D:\Program Files\Unity\Editor\Data\MonoBleedingEdge\lib\mono\4.7.1-api\System.Data.dll'. Remove one of the duplicate references.  </p>
  </blockquote>
  
  <p>And also, the same Exception occurred in the other directory: </p>
  
  <p><code>D:\Program Files\Unity\Editor\Data\NetStandard\compat\2.0.0\shims\netfx\</code></p>
  
  <p>At that time, in order to solve the problem, I removed the System.Data.dll in both two directories and then I can use the namespace System.Data in the Visual Studio 2017. But when I use <code>System.Data.ConnectionState</code>, there is an another error:  </p>
  
  <blockquote>
    <p>Assets\Scripts\DBConnection.cs(39,35): error CS0433: The type 'ConnectionState' exists in both 'System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' and 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'  </p>
  </blockquote>
  
  <p>After many methods were tried, I found if I entered  </p>
  
  <p><code>Edit --&gt; Project Settings --&gt; Player --&gt; Other Settings --&gt; Configuration --&gt; Api Compatibility Level</code></p>
  
  <p>and turned .Net Standard 2.0 to .Net 4.x, the error could be avoid.
  But is this method right? After doing this I still can’t access the database because many Exceptions occurred(Most of them are about <code>SqlConnection</code>).  </p>
  
  <p>There might be many problems in my method, but can anyone please tell me what the right method is?  </p>
  
  <p>Thanks very much.</p>