Composed query with groupBy clause in subquery fails

[simontreanor]

Describe the bug SqlException "Only one expression can be specified in the select list when the subquery is not introduced with EXISTS." returned when using a composed query when the subquery has a groupBy clause. This is because SQLProvider includes the groupBy key in the select clause even if you haven't asked for it.

To Reproduce Steps to reproduce the behavior:

1. Take a query that uses a subquery with a groupBy clause, e.g.:

let test =
    let lastAddresses =
        query {
            for a in dbContext.Address do
            where (a.Deleted.IsNone)
            groupBy a.UserId into g
            select (g.Max(fun a -> a.Id))
        }
    let result =
        query {
            for a in dbContext.Address do
            where (lastAddresses.Contains(a.Id))
            select a
        }
    result

2. Run the query, and you get the SqlException described above.
3. Inspecting the SQL produced, you can see the problem:

SELECT *
FROM [address] as [a] 
WHERE (([a].[Id] IN (
    SELECT [a].[UserId] as '[a].[UserId]', MAX([a].[Id]) as '[a].[MAX_Id]'
    FROM [address] as [a]
    WHERE (([a].[Deleted] IS NOT NULL))
    GROUP BY [a].[UserId]))
)

4. Basically SQLProvider is including [a].[UserId] as '[a].[UserId]' in the select clause of the subquery. The IN clause is only expecting a single column in the subquery so fails.

Expected behavior

SQLProvider should only return the columns requested in the query. The SQL produced should be:

SELECT *
FROM [address] as [a] 
WHERE (([a].[Id] IN (
    SELECT MAX([a].[Id]) as '[a].[MAX_Id]'
    FROM [address] as [a]
    WHERE (([a].[Deleted] IS NOT NULL))
    GROUP BY [a].[UserId]))
)

Additional context If we wanted the groupBy key included in the select statement, we could do so by requesting it explicitly, so there is no reason why SQLProvider should do this for us unsolicitedly:

let test =
    let lastAddresses =
        query {
            for a in dbContext.Address do
            where (a.Deleted.IsNone)
            groupBy a.UserId into g
            select (g.Key, g.Max(fun a -> a.Id))
        }
    let result =
        query {
            for a in dbContext.Address do
            where (lastAddresses.Contains(a.Id))
            select a
        }
    result