Aggregates on multiple child tables produces invalid SQL

[jmussett]

Doing a .Select on multiple aggregates of different child tables after a .GroupBy produces invalid SQL.

Steps to reproduce

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="6.0.1" />
  </ItemGroup>
</Project>

using Microsoft.EntityFrameworkCore;
using System.Linq;

class Program
{
	public class Parent
	{
		public int Id { get; set; }
		public Child1 Child1 { get; set; }
		public Child2 Child2 { get; set; }
	}

	public class Child1
	{
		public int Id { get; set; }
		public string Value1 { get; set; }
	}

	public class Child2
	{
		public int Id { get; set; }
		public string Value2 { get; set; }
	}

	public class TestDb : DbContext
	{
		public DbSet<Parent> Table { get; set; }
		protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
		{
			optionsBuilder.UseSqlServer("data source=dummy");
		}
	}
	static void Main()
	{
		using var db = new TestDb();

		var q = db.Table
			.GroupBy(x => new { })
			.Select(g => new
			{
				Test1 = g
					.Select(x => x.Child1.Value1)
					.Distinct()
					.Count(),
				Test2 = g
					.Select(x => x.Child2.Value2)
					.Distinct()
					.Count()
			});

		var sql = q.ToQueryString();
	}
}

Expected translation (Approximation):

SELECT COUNT(DISTINCT ([c].[Value1])) AS [Test1], COUNT(DISTINCT ([c2].[Value2])) AS [Test2]
FROM (
    SELECT [t].[Child1Id], [t].[Child2Id], 1 AS [Key]
    FROM [Table] AS [t]
) AS [t0]
LEFT JOIN [Child1] AS [c] ON [t0].[Child1Id] = [c].[Id]
LEFT JOIN [Child2] AS [c2] ON [t0].[Child2Id] = [c2].[Id]
GROUP BY [t0].[Key]

Actual translation:

SELECT COUNT(DISTINCT ([c].[Value1])) AS [Test1], COUNT(DISTINCT ([c].[Value2])) AS [Test2]
FROM (
    SELECT [t].[Child1Id], 1 AS [Key]
    FROM [Table] AS [t]
) AS [t0]
LEFT JOIN [Child1] AS [c] ON [t0].[Child1Id] = [c].[Id]
GROUP BY [t0].[Key]

Provider and version information

EF Core version: 6.0.1
Database provider: Microsoft.EntityFrameworkCore.SqlServer 6.0.1
Target framework: .NET 6.0
Operating system: Windows 10 Pro
IDE: Visual Studio 2022 17.0.1