Good day, Prompt please how to work with System.Data.OleDb, create sript C # and I wrote that did not see this library. I'm using Framework.
My first thought is that the version of Mono used in Unity doesn't implement that namespace. Because Unity is built on Mono (an open source library that mimics the functionality of .NET) and not .NET itself, you're limited to whatever was finished and working in the release version used, in Unity's case version 1.2.5. I can't seem to find the page in the Mono docs to confirm whether this namespace is implemented or not, but MoMA is a free tool to check compatibility of .NET projects in Mono. Don't know if it would help in this case, but you could try building a simple program in Visual Studio using that namespace and run it through MoMA (version 1.2.5) to see if it's implemented.
Try to find System.Data.OleDb's dll file in microsofts .NET and just copy it to your projects Assets folder. "Should" work... Please let us all know how it goes. Seems like a very common issue.