Refactor query SQL generation for standardization

* GenerateTop() implementation moved to SqlServer
* GenerateLimitOffset() generates ISO SQL:2008 by default, overridden
  by SqlServer (and Sqlite)

src/EFCore.Relational/Query/Pipeline/QuerySqlGenerator.cs

@@ -531,19 +531,12 @@ protected virtual string GenerateOperator(SqlBinaryExpression binaryExpression)
 
  protected virtual void GenerateTop(SelectExpression selectExpression)
  {
- if (selectExpression.Limit != null
- && selectExpression.Offset == null)
- {
- _relationalCommandBuilder.Append("TOP(");
-
- Visit(selectExpression.Limit);
-
- _relationalCommandBuilder.Append(") ");
- }
  }
 
  protected virtual void GenerateLimitOffset(SelectExpression selectExpression)
  {
+ // The below implements ISO SQL:2008
+
  if (selectExpression.Offset != null)
  {
  _relationalCommandBuilder.AppendLine()
@@ -562,6 +555,15 @@ protected virtual void GenerateLimitOffset(SelectExpression selectExpression)
  _relationalCommandBuilder.Append(" ROWS ONLY");
  }
  }
+ else if (selectExpression.Limit != null)
+ {
+ _relationalCommandBuilder.AppendLine()
+ .Append("FETCH FIRST ");
+
+ Visit(selectExpression.Limit);
+
+ _relationalCommandBuilder.Append(" ROWS ONLY");
+ }
  }
 
  private void GenerateList<T>(

src/EFCore.SqlServer/Extensions/SqlServerServiceCollectionExtensions.cs

@@ -90,6 +90,7 @@ public static IServiceCollection AddEntityFrameworkSqlServer([NotNull] this ISer
  // New Query Pipeline
  .TryAdd<IMethodCallTranslatorProvider, SqlServerMethodCallTranslatorProvider>()
  .TryAdd<IMemberTranslatorProvider, SqlServerMemberTranslatorProvider>()
+ .TryAdd<IQuerySqlGeneratorFactory, SqlServerQuerySqlGeneratorFactory>()
  .TryAdd<IShapedQueryOptimizerFactory, SqlServerShapedQueryOptimizerFactory>()
  .TryAdd<IRelationalSqlTranslatingExpressionVisitorFactory, SqlServerSqlTranslatingExpressionVisitorFactory>()
 

src/EFCore.SqlServer/Query/Pipeline/SqlServerQuerySqlGenerator.cs

@@ -0,0 +1,55 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.EntityFrameworkCore.Relational.Query.Pipeline;
+using Microsoft.EntityFrameworkCore.Relational.Query.Pipeline.SqlExpressions;
+using Microsoft.EntityFrameworkCore.Storage;
+
+namespace Microsoft.EntityFrameworkCore.SqlServer.Query.Pipeline
+{
+ public class SqlServerQuerySqlGenerator : QuerySqlGenerator
+ {
+ public SqlServerQuerySqlGenerator(
+ IRelationalCommandBuilderFactory relationalCommandBuilderFactory,
+ ISqlGenerationHelper sqlGenerationHelper)
+ : base(relationalCommandBuilderFactory, sqlGenerationHelper)
+ {
+ }
+
+ protected override void GenerateTop(SelectExpression selectExpression)
+ {
+ if (selectExpression.Limit != null
+ && selectExpression.Offset == null)
+ {
+ Sql.Append("TOP(");
+
+ Visit(selectExpression.Limit);
+
+ Sql.Append(") ");
+ }
+ }
+
+ protected override void GenerateLimitOffset(SelectExpression selectExpression)
+ {
+ // Note: For Limit without Offset, SqlServer generates TOP()
+ if (selectExpression.Offset != null)
+ {
+ Sql.AppendLine()
+ .Append("OFFSET ");
+
+ Visit(selectExpression.Offset);
+
+ Sql.Append(" ROWS");
+
+ if (selectExpression.Limit != null)
+ {
+ Sql.Append(" FETCH NEXT ");
+
+ Visit(selectExpression.Limit);
+
+ Sql.Append(" ROWS ONLY");
+ }
+ }
+ }
+ }
+}

src/EFCore.SqlServer/Query/Pipeline/SqlServerQuerySqlGeneratorFactory.cs

@@ -0,0 +1,26 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.EntityFrameworkCore.Relational.Query.Pipeline;
+using Microsoft.EntityFrameworkCore.Storage;
+
+namespace Microsoft.EntityFrameworkCore.SqlServer.Query.Pipeline
+{
+ public class SqlServerQuerySqlGeneratorFactory : QuerySqlGeneratorFactory
+ {
+ private readonly IRelationalCommandBuilderFactory _commandBuilderFactory;
+ private readonly ISqlGenerationHelper _sqlGenerationHelper;
+
+ public SqlServerQuerySqlGeneratorFactory(
+ IRelationalCommandBuilderFactory commandBuilderFactory,
+ ISqlGenerationHelper sqlGenerationHelper)
+ : base(commandBuilderFactory, sqlGenerationHelper)
+ {
+ _commandBuilderFactory = commandBuilderFactory;
+ _sqlGenerationHelper = sqlGenerationHelper;
+ }
+
+ public override QuerySqlGenerator Create()
+ => new SqlServerQuerySqlGenerator(_commandBuilderFactory, _sqlGenerationHelper);
+ }
+}

src/EFCore.Sqlite.Core/Query/Pipeline/SqliteQuerySqlGenerator.cs

@@ -24,11 +24,6 @@ protected override string GenerateOperator(SqlBinaryExpression binaryExpression)
  ? " || "
  : base.GenerateOperator(binaryExpression);
 
- protected override void GenerateTop(SelectExpression selectExpression)
- {
- // Handled by GenerateLimitOffset
- }
-
  protected override void GenerateLimitOffset(SelectExpression selectExpression)
  {
  Check.NotNull(selectExpression, nameof(selectExpression));

src/EFCore.Sqlite.Core/Query/Pipeline/SqliteQuerySqlGeneratorFactory2.cs → src/EFCore.Sqlite.Core/Query/Pipeline/SqliteQuerySqlGeneratorFactory.cs

@@ -21,8 +21,6 @@ public SqliteQuerySqlGeneratorFactory(
  }
 
  public override QuerySqlGenerator Create()
- {
- return new SqliteQuerySqlGenerator(_commandBuilderFactory, _sqlGenerationHelper);
- }
+ => new SqliteQuerySqlGenerator(_commandBuilderFactory, _sqlGenerationHelper);
  }
 }