Query: Improve alias-ing of projection in SelectExpression

Issue: When we try to find name of the projection, we go through Convert/NullableExpression nodes. But when updating the alias we just wrap it inside a new AliasExpression. If the inner expression had AliasExpression giving it a name, then we would have multiple "AS" in SQL
Fix: When assigning new alias to projection, we run visitor and tries to replace old name to new name to avoid multiple aliases.

Resolves #11757

src/EFCore.Relational/Query/Expressions/SelectExpression.cs

@@ -760,16 +760,20 @@ var currentProjectionIndex
 
  var updatedExpression = expression;
 
- if (!(expression is ColumnReferenceExpression
- || expression is ColumnExpression
- || expression is AliasExpression)
+ // All subquery projections are required to be ColumnExpression/ColumnReferenceExpression/AliasExpression
+ if (!(updatedExpression is ColumnExpression
+ || updatedExpression is ColumnReferenceExpression
+ || updatedExpression is AliasExpression)
  || !string.Equals(currentAlias, uniqueAlias, StringComparison.OrdinalIgnoreCase))
  {
- updatedExpression = new AliasExpression(uniqueAlias, (expression as AliasExpression)?.Expression ?? expression);
+ var newExpression = new NameReplacingExpressionVisitor(currentAlias, uniqueAlias)
+ .Visit(updatedExpression);
+ updatedExpression = newExpression != updatedExpression
+ ? newExpression
+ : new AliasExpression(uniqueAlias, updatedExpression);
  }
 
  var currentOrderingIndex = _orderBy.FindIndex(e => e.Expression.Equals(expression));
-
  if (currentOrderingIndex != -1)
  {
  var oldOrdering = _orderBy[currentOrderingIndex];
@@ -786,6 +790,30 @@ var currentProjectionIndex
  return updatedExpression;
  }
 
+ private class NameReplacingExpressionVisitor : ExpressionVisitor
+ {
+ private readonly string _oldName;
+ private readonly string _newName;
+
+ public NameReplacingExpressionVisitor(string oldName, string newName)
+ {
+ _oldName = oldName;
+ _newName = newName;
+ }
+
+ protected override Expression VisitExtension(Expression extensionExpression)
+ {
+ switch (extensionExpression)
+ {
+ case AliasExpression aliasExpression
+ when string.Equals(aliasExpression.Alias, _oldName, StringComparison.OrdinalIgnoreCase):
+ return new AliasExpression(_newName, aliasExpression.Expression);
+ }
+
+ return base.VisitExtension(extensionExpression);
+ }
+ }
+
  private static string GetColumnName(Expression expression)
  {
  expression = expression.RemoveConvert();

src/EFCore.Specification.Tests/Query/AsyncGroupByQueryTestBase.cs

@@ -906,10 +906,11 @@ await AssertQuery<Order, Customer>(
  (from c in cs
  join o in os
  on c.CustomerID equals o.CustomerID into grouping
- from o in grouping
+ from o in grouping.DefaultIfEmpty()
+ where o != null
  select o)
  .GroupBy(o => o.CustomerID)
- .Select(g => new { g.Key, Count = g.Average(o => o.OrderID) }),
+ .Select(g => new { g.Key, Average = g.Average(o => o.OrderID) }),
  e => e.Key);
  }
 
@@ -921,10 +922,10 @@ await AssertQuery<Order, Customer>(
  (from c in cs
  join o in os
  on c.CustomerID equals o.CustomerID into grouping
- from o in grouping
+ from o in grouping.DefaultIfEmpty()
  select c)
  .GroupBy(c => c.CustomerID)
- .Select(g => new { g.Key, Count = g.Max(c => c.City) }),
+ .Select(g => new { g.Key, Max = g.Max(c => c.City) }),
  e => e.Key);
  }
 
@@ -936,13 +937,43 @@ await AssertQuery<Order, Customer>(
  (from o in os
  join c in cs
  on o.CustomerID equals c.CustomerID into grouping
- from c in grouping
+ from c in grouping.DefaultIfEmpty()
  select o)
  .GroupBy(o => o.CustomerID)
- .Select(g => new { g.Key, Count = g.Average(o => o.OrderID) }),
+ .Select(g => new { g.Key, Average = g.Average(o => o.OrderID) }),
  e => e.Key);
  }
 
+ [ConditionalFact]
+ public virtual async Task GroupJoin_GroupBy_Aggregate_4()
+ {
+ await AssertQuery<Order, Customer>(
+ (os, cs) =>
+ (from c in cs
+ join o in os
+ on c.CustomerID equals o.CustomerID into grouping
+ from o in grouping.DefaultIfEmpty()
+ select c)
+ .GroupBy(c => c.CustomerID)
+ .Select(g => new { Value = g.Key, Max = g.Max(c => c.City) }),
+ e => e.Value);
+ }
+
+ [ConditionalFact]
+ public virtual async Task GroupJoin_GroupBy_Aggregate_5()
+ {
+ await AssertQuery<Order, Customer>(
+ (os, cs) =>
+ (from o in os
+ join c in cs
+ on o.CustomerID equals c.CustomerID into grouping
+ from c in grouping.DefaultIfEmpty()
+ select o)
+ .GroupBy(o => o.OrderID)
+ .Select(g => new { Value = g.Key, Average = g.Average(o => o.OrderID) }),
+ e => e.Value);
+ }
+
  [ConditionalFact]
  public virtual async Task GroupBy_optional_navigation_member_Aggregate()
  {

src/EFCore.Specification.Tests/Query/GroupByQueryTestBase.cs

@@ -909,10 +909,11 @@ public virtual void GroupJoin_GroupBy_Aggregate()
  (from c in cs
  join o in os
  on c.CustomerID equals o.CustomerID into grouping
- from o in grouping
+ from o in grouping.DefaultIfEmpty()
+ where o != null
  select o)
  .GroupBy(o => o.CustomerID)
- .Select(g => new { g.Key, Count = g.Average(o => o.OrderID) }),
+ .Select(g => new { g.Key, Average = g.Average(o => o.OrderID) }),
  e => e.Key);
  }
 
@@ -924,10 +925,10 @@ public virtual void GroupJoin_GroupBy_Aggregate_2()
  (from c in cs
  join o in os
  on c.CustomerID equals o.CustomerID into grouping
- from o in grouping
+ from o in grouping.DefaultIfEmpty()
  select c)
  .GroupBy(c => c.CustomerID)
- .Select(g => new { g.Key, Count = g.Max(c => c.City) }),
+ .Select(g => new { g.Key, Max = g.Max(c => c.City) }),
  e => e.Key);
  }
 
@@ -939,13 +940,43 @@ public virtual void GroupJoin_GroupBy_Aggregate_3()
  (from o in os
  join c in cs
  on o.CustomerID equals c.CustomerID into grouping
- from c in grouping
+ from c in grouping.DefaultIfEmpty()
  select o)
  .GroupBy(o => o.CustomerID)
- .Select(g => new { g.Key, Count = g.Average(o => o.OrderID) }),
+ .Select(g => new { g.Key, Average = g.Average(o => o.OrderID) }),
  e => e.Key);
  }
 
+ [ConditionalFact]
+ public virtual void GroupJoin_GroupBy_Aggregate_4()
+ {
+ AssertQuery<Order, Customer>(
+ (os, cs) =>
+ (from c in cs
+ join o in os
+ on c.CustomerID equals o.CustomerID into grouping
+ from o in grouping.DefaultIfEmpty()
+ select c)
+ .GroupBy(c => c.CustomerID)
+ .Select(g => new { Value = g.Key, Max = g.Max(c => c.City) }),
+ e => e.Value);
+ }
+
+ [ConditionalFact]
+ public virtual void GroupJoin_GroupBy_Aggregate_5()
+ {
+ AssertQuery<Order, Customer>(
+ (os, cs) =>
+ (from o in os
+ join c in cs
+ on o.CustomerID equals c.CustomerID into grouping
+ from c in grouping.DefaultIfEmpty()
+ select o)
+ .GroupBy(o => o.OrderID)
+ .Select(g => new { Value = g.Key, Average = g.Average(o => o.OrderID) }),
+ e => e.Value);
+ }
+
  [ConditionalFact]
  public virtual void GroupBy_optional_navigation_member_Aggregate()
  {

test/EFCore.SqlServer.FunctionalTests/Query/GroupByQuerySqlServerTest.cs

@@ -810,9 +810,10 @@ public override void GroupJoin_GroupBy_Aggregate()
  base.GroupJoin_GroupBy_Aggregate();
 
  AssertSql(
- @"SELECT [o].[CustomerID] AS [Key], AVG(CAST([o].[OrderID] AS float)) AS [Count]
+ @"SELECT [o].[CustomerID] AS [Key], AVG(CAST([o].[OrderID] AS float)) AS [Average]
 FROM [Customers] AS [c]
-INNER JOIN [Orders] AS [o] ON [c].[CustomerID] = [o].[CustomerID]
+LEFT JOIN [Orders] AS [o] ON [c].[CustomerID] = [o].[CustomerID]
+WHERE [o].[OrderID] IS NOT NULL
 GROUP BY [o].[CustomerID]");
  }
 
@@ -821,9 +822,9 @@ public override void GroupJoin_GroupBy_Aggregate_2()
  base.GroupJoin_GroupBy_Aggregate_2();
 
  AssertSql(
- @"SELECT [c].[CustomerID] AS [Key], MAX([c].[City]) AS [Count]
+ @"SELECT [c].[CustomerID] AS [Key], MAX([c].[City]) AS [Max]
 FROM [Customers] AS [c]
-INNER JOIN [Orders] AS [o] ON [c].[CustomerID] = [o].[CustomerID]
+LEFT JOIN [Orders] AS [o] ON [c].[CustomerID] = [o].[CustomerID]
 GROUP BY [c].[CustomerID]");
  }
 
@@ -832,12 +833,35 @@ public override void GroupJoin_GroupBy_Aggregate_3()
  base.GroupJoin_GroupBy_Aggregate_3();
 
  AssertSql(
- @"SELECT [o].[CustomerID] AS [Key], AVG(CAST([o].[OrderID] AS float)) AS [Count]
+ @"SELECT [o].[CustomerID] AS [Key], AVG(CAST([o].[OrderID] AS float)) AS [Average]
 FROM [Orders] AS [o]
-INNER JOIN [Customers] AS [c] ON [o].[CustomerID] = [c].[CustomerID]
+LEFT JOIN [Customers] AS [c] ON [o].[CustomerID] = [c].[CustomerID]
 GROUP BY [o].[CustomerID]");
  }
 
+ public override void GroupJoin_GroupBy_Aggregate_4()
+ {
+ base.GroupJoin_GroupBy_Aggregate_4();
+
+ AssertSql(
+ @"SELECT [c].[CustomerID] AS [Value], MAX([c].[City]) AS [Max]
+FROM [Customers] AS [c]
+LEFT JOIN [Orders] AS [o] ON [c].[CustomerID] = [o].[CustomerID]
+GROUP BY [c].[CustomerID]");
+ }
+
+ public override void GroupJoin_GroupBy_Aggregate_5()
+ {
+ base.GroupJoin_GroupBy_Aggregate_5();
+
+ AssertSql(
+ @"SELECT [o].[OrderID] AS [Value], AVG(CAST([o].[OrderID] AS float)) AS [Average]
+FROM [Orders] AS [o]
+LEFT JOIN [Customers] AS [c] ON [o].[CustomerID] = [c].[CustomerID]
+GROUP BY [o].[OrderID]");
+
+ }
+
  public override void GroupBy_optional_navigation_member_Aggregate()
  {
  base.GroupBy_optional_navigation_member_Aggregate();