How to make two SQL queries really asynchronous

Here's a way to to perform two tasks asynchronously and in parallel:

Task<int> accountTask = GetAccounts();
Task<int> depositsTask = GetDeposits();

int[] results = await Task.WhenAll(accountTask, depositsTask);

int accounts = results[0];
int deposits = results[1];

When you use the Result property on a task that hasn't completed yet the calling thread will block until the operation completes. That means in your case that the GetAccounts operation need to complete before the call to GetDeposits starts.

If you want to make sure these method are parallel (including the synchronous CPU-intensive parts) you need to offload that work to another thread. The simplest way to do so would be to use Task.Run:

static async Task Main()
{
    var accountTask = Task.Run(async () => Console.WriteLine(await GetAccounts()));
    var depositsTask = Task.Run(async () => Console.WriteLine(await GetDeposits()));

    await Task.WhenAll(accountTask, depositsTask);
}

I generally prefer to use Task.WaitAll. To setup for this code segment, I changed the GetAccounts/GetDeposits signatures just to return int (public static int GetAccounts())

I placed the Console.WriteLine in the same thread as assigning the return to validate that one GetDeposits returns before GetAccounts has, but this is unnecessary and probably best to move it after the Task.WaitAll

     private static void Main(string[] args) {

        int getAccountsTask = 0;
        int getDepositsTask = 0;
        List<Task> tasks = new List<Task>() {
            Task.Factory.StartNew(() => {
                getAccountsTask = GetAccounts();
                Console.WriteLine(getAccountsTask);
            }),
            Task.Factory.StartNew(() => {
                getDepositsTask = GetDeposits();
                Console.WriteLine(getDepositsTask);

            })

        };
        Task.WaitAll(tasks.ToArray());



    }