Why can't use SQLProvider connect to SqlServer and get data?

Question

I try to use sqlprovider to get data from sqlserver:

https://github.com/fsprojects/SQLProvider

I have installed SqlServer 2008 r2,everything is ok,I create database a,table b with field x,y

I use vs.net 2017,installed SQLProvider

Install-Package SQLProvider

then write code:

open FSharp.Data.Sql    

type Sqlmdf = SqlDataProvider<
Common.DatabaseProviderTypes.MSSQLSERVER,
"Server=localhost;Database=a;Trusted_Connection=True"
>

let dbm = Sqlmdf.GetDataContext()

let res=
query{
    for c in dbm.
}

in example of http://fsprojects.github.io/SQLProvider/

because I create table "b",so after type dbm. ,vs.net will show me table name "b",but it only show me Equals,ToString,GetType,GetHashCode four method

so what's wrong?vs.net,or sqlprovider itself?Thanks!

First I don't want to use sqlservr,I want to use sqlite or mysql,but the connect string is hard to understand,I want to use NORTHWND.mdf ,or sqlserver localDB,but failed too,vs.net can't show me the table name