GroupBy debug assert: Missing alias in the list: p1,p

Found working on samples for RC1, then running them as tests on main.

System.InvalidOperationException
Missing alias in the list: p1,p
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryTranslationPostprocessor.TableAliasVerifyingExpressionVisitor.ScopedVisitor.EntryPoint(Expression expression) in C:\dotnet\efcore\src\EFCore.Relational\Query\RelationalQueryTranslationPostprocessor.cs:line 128
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryTranslationPostprocessor.TableAliasVerifyingExpressionVisitor.UniquifyAliasInSelectExpression(Expression selectExpression) in C:\dotnet\efcore\src\EFCore.Relational\Query\RelationalQueryTranslationPostprocessor.cs:line 104
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryTranslationPostprocessor.TableAliasVerifyingExpressionVisitor.Visit(Expression expression) in C:\dotnet\efcore\src\EFCore.Relational\Query\RelationalQueryTranslationPostprocessor.cs:line 89
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryTranslationPostprocessor.Process(Expression query) in C:\dotnet\efcore\src\EFCore.Relational\Query\RelationalQueryTranslationPostprocessor.cs:line 52
   at Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query) in C:\dotnet\efcore\src\EFCore\Query\QueryCompilationContext.cs:line 190
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Boolean async) in C:\dotnet\efcore\src\EFCore\Storage\Database.cs:line 76
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](IDatabase database, Expression query, IModel model, Boolean async) in C:\dotnet\efcore\src\EFCore\Query\Internal\QueryCompiler.cs:line 111
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass9_0`1.<Execute>b__0() in C:\dotnet\efcore\src\EFCore\Query\Internal\QueryCompiler.cs:line 95
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler) in C:\dotnet\efcore\src\EFCore\Query\Internal\CompiledQueryCache.cs:line 74
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query) in C:\dotnet\efcore\src\EFCore\Query\Internal\QueryCompiler.cs:line 91
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression) in C:\dotnet\efcore\src\EFCore\Query\Internal\EntityQueryProvider.cs:line 78
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1.GetEnumerator() in C:\dotnet\efcore\src\EFCore\Query\Internal\EntityQueryable`.cs:line 90
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at GroupBySample.Translate_GroupBy_followed_by_FirstOrDefault_over_group() in C:\dotnet\efcore\test\EFCore.SqlServer.FunctionalTests\SqlServerEndToEndTest.cs:line 31

public class GroupBySample
{
    [ConditionalFact]
    public void Translate_GroupBy_followed_by_FirstOrDefault_over_group()
    {
        Console.WriteLine($">>>> Sample: {nameof(Translate_GroupBy_followed_by_FirstOrDefault_over_group)}");
        Console.WriteLine();

        Helpers.RecreateCleanDatabase();
        Helpers.PopulateDatabase();

        // Example 3. From #12640
        using (var context = new ShoesContext())
        {
            #region GroupBy3
            var people = context.People
                .Where(e => e.MiddleInitial == "Q" && e.Age == 20)
                .GroupBy(e => e.LastName)
                .Select(g => g.First().LastName)
                .OrderBy(e => e.Length)
                .ToList();
            #endregion
        
            Console.WriteLine();
        
            foreach (var person in people)
            {
                Console.WriteLine(person);
            }
        
            Console.WriteLine();
        }
        
        // Example 5. From #12601
        using (var context = new ShoesContext())
        {
            #region GroupBy5
            var results = context.People
                .GroupBy(e => e.FirstName)
                .Select(g => g.First().LastName)
                .OrderBy(e => e)
                .ToList();
            #endregion
        
            Console.WriteLine();
            
            foreach (var result in results)
            {
                Console.WriteLine(result);
            }
        
            Console.WriteLine();
        }

        // Example 6. From #12600
        using (var context = new ShoesContext())
        {
            #region GrouoBy6
            var results = context.People.Where(e => e.Age == 20)
                .GroupBy(e => e.Id)
                .Select(g => g.First().MiddleInitial)
                .OrderBy(e => e)
                .ToList();
            #endregion
        
            Console.WriteLine();
        
            foreach (var result in results)
            {
                Console.WriteLine(result);
            }
        
            Console.WriteLine();
        }
    }

    public static class Helpers
    {
        public static void RecreateCleanDatabase()
        {
            using var context = new ShoesContext(quiet: true);

            context.Database.EnsureDeleted();
            context.Database.EnsureCreated();
        }

        public static void PopulateDatabase()
        {
            using var context = new ShoesContext(quiet: true);

            context.AddRange(
                new Person
                {
                    FirstName = "Jim",
                    MiddleInitial = "A",
                    LastName = "Bob",
                    Age = 20,
                    Feet = new Feet { Size = 11 },
                    Shoes = { new() { Style = "Sneakers", Age = 19 }, new() { Style = "Dress", Age = 20 } }
                },
                new Person
                {
                    FirstName = "Tom",
                    MiddleInitial = "A",
                    LastName = "Bob",
                    Age = 20,
                    Feet = new Feet { Size = 12 },
                    Shoes = { new() { Style = "Sneakers", Age = 21 }, new() { Style = "Dress", Age = 19 } }
                },
                new Person
                {
                    FirstName = "Ben",
                    MiddleInitial = "Q",
                    LastName = "Bob",
                    Age = 20,
                    Feet = new Feet { Size = 12 },
                    Shoes = { new() { Style = "Sneakers", Age = 20 }, new() { Style = "Dress", Age = 21 } }
                },
                new Person
                {
                    FirstName = "Jim",
                    MiddleInitial = "Q",
                    LastName = "Jon",
                    Age = 20,
                    Feet = new Feet { Size = 11 },
                    Shoes = { new() { Style = "Sneakers", Age = 19 }, new() { Style = "Dress", Age = 20 } }
                },
                new Person
                {
                    FirstName = "Tom",
                    MiddleInitial = "A",
                    LastName = "Jon",
                    Age = 21,
                    Feet = new Feet { Size = 11 },
                    Shoes = { new() { Style = "Sneakers", Age = 21 }, new() { Style = "Dress", Age = 19 } }
                },
                new Person
                {
                    FirstName = "Ben",
                    MiddleInitial = "A",
                    LastName = "Jon",
                    Age = 21,
                    Feet = new Feet { Size = 12 },
                    Shoes = { new() { Style = "Sneakers", Age = 20 }, new() { Style = "Dress", Age = 21 } }
                },
                new Person
                {
                    FirstName = "Jim",
                    MiddleInitial = "Q",
                    LastName = "Don",
                    Age = 21,
                    Feet = new Feet { Size = 12 },
                    Shoes = { new() { Style = "Sneakers", Age = 19 }, new() { Style = "Dress", Age = 20 } }
                },
                new Person
                {
                    FirstName = "Tom",
                    MiddleInitial = "Q",
                    LastName = "Don",
                    Age = 21,
                    Feet = new Feet { Size = 11 },
                    Shoes = { new() { Style = "Sneakers", Age = 21 }, new() { Style = "Dress", Age = 19 } }
                },
                new Person
                {
                    FirstName = "Ben",
                    MiddleInitial = "A",
                    LastName = "Don",
                    Age = 21,
                    Feet = new Feet { Size = 11 },
                    Shoes = { new() { Style = "Sneakers", Age = 20 }, new() { Style = "Dress", Age = 21 } }
                },
                new Person
                {
                    FirstName = "Jim",
                    MiddleInitial = "A",
                    LastName = "Zee",
                    Age = 21,
                    Feet = new Feet { Size = 12 },
                    Shoes = { new() { Style = "Sneakers", Age = 19 }, new() { Style = "Dress", Age = 20 } }
                },
                new Person
                {
                    FirstName = "Tom",
                    MiddleInitial = "Q",
                    LastName = "Zee",
                    Age = 21,
                    Feet = new Feet { Size = 12 },
                    Shoes = { new() { Style = "Sneakers", Age = 21 }, new() { Style = "Dress", Age = 19 } }
                },
                new Person
                {
                    FirstName = "Ben",
                    MiddleInitial = "Q",
                    LastName = "Zee",
                    Age = 21,
                    Feet = new Feet { Size = 11 },
                    Shoes = { new() { Style = "Sneakers", Age = 20 }, new() { Style = "Dress", Age = 21 } }
                });

            context.SaveChanges();
        }
    }

    #region Model
    public class Person
    {
        public int Id { get; set; }
        public int Age { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string MiddleInitial { get; set; }
        public Feet Feet { get; set; }
        public ICollection<Shoes> Shoes { get; } = new List<Shoes>();
    }

    public class Shoes
    {
        public int Id { get; set; }
        public int Age { get; set; }
        public string Style { get; set; }
        public Person Person { get; set; }
    }

    public class Feet
    {
        public int Id { get; set; }
        public int Size { get; set; }
        public Person Person { get; set; }
    }
    #endregion

    public class ShoesContext : DbContext
    {
        public DbSet<Person> People { get; set; }
        public DbSet<Shoes> Shoes { get; set; }
        public DbSet<Feet> Feet { get; set; }

        private readonly bool _quiet;

        public ShoesContext(bool quiet = false)
        {
            _quiet = quiet;
        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder
                .EnableSensitiveDataLogging()
                .UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=EFCoreSample");

            if (!_quiet)
            {
                optionsBuilder.LogTo(Console.WriteLine, new[] { RelationalEventId.CommandExecuted });
            }
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Feet>().HasOne(e => e.Person).WithOne(e => e.Feet).HasForeignKey<Feet>();
        }
    }
}

[smitpatel]

.Select(g => g.First().LastName)
                .OrderBy(e => e.Length)

is the core issue. The selector needs to be something which is a scalar single result value so it gets lifted in projection and ordering is applied afterwards which copies earlier select and they both ends up getting shared so earlier alias is gone from the tree. Overlaps with #20291 #7776 #18775 Since this is debug only check, we can differ to next release.

[smitpatel]

Attempted to fix this by cloning SqlExpression when getting it through projection during Sql translation (so that composed fragment differs from projection causing them not to overwrite the aliases), but that cause issues because we need to identify both of them as same when pushing down subquery so that aggregate operation is lifted inside group by rather than as a subquery outside the group by query. Since it makes SQL worse, this approach may not be right choice.

Re-visit with pending selector work.