Query: Distinct followed by other operations can give rise to incorrect SQL

[smitpatel]

SQL generated by following tests is invalid and throws exception.
There can be more variations which may fail too.

[ConditionalFact]
public virtual void OrderBy_coalesce_take_distinct()
{
	AssertQuery<Product>(
		ps => ps.OrderBy(p => p.UnitPrice ?? 0)
			.Take(15)
			.Distinct()
			.Select(p => new {Price = p.UnitPrice ?? 0}),
		assertOrder: false,
		entryCount: 15);
}


[ConditionalFact]
public virtual void OrderBy_skip_take_distinct()
{
	AssertQuery<Customer>(
		cs => cs.OrderBy(c => c.ContactTitle)
			.ThenBy(c => c.ContactName)
			.Skip(5)
			.Take(15)
			.Distinct()
			.OrderBy(c => c.ContactTitle)
			.Take(8),
		assertOrder: false,
		entryCount: 8);
}