Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Data.Linq/SqlClient/Query/SqlRewriteScalarSubqueries.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Collections.Generic;
+using System.Linq.Expressions;
+using System.Data.Linq;
+
+namespace System.Data.Linq.SqlClient {
+
+    // converts correlated scalar subqueries into outer-applies
+    // must be run after flattener.
+    internal class SqlRewriteScalarSubqueries {
+        Visitor visitor;
+
+        internal SqlRewriteScalarSubqueries(SqlFactory sqlFactory) {
+            this.visitor = new Visitor(sqlFactory);
+        }
+
+        internal SqlNode Rewrite(SqlNode node) {
+            return this.visitor.Visit(node);
+        }
+
+        class Visitor : SqlVisitor {
+            SqlFactory sql;
+            SqlSelect currentSelect;
+            SqlAggregateChecker aggregateChecker;
+
+            internal Visitor(SqlFactory sqlFactory) {
+                this.sql = sqlFactory;
+                this.aggregateChecker = new SqlAggregateChecker();
+            }
+
+            internal override SqlExpression VisitScalarSubSelect(SqlSubSelect ss) {
+                SqlSelect innerSelect = this.VisitSelect(ss.Select);
+                if (!this.aggregateChecker.HasAggregates(innerSelect)) {
+                    innerSelect.Top = this.sql.ValueFromObject(1, ss.SourceExpression);
+                }
+                innerSelect.OrderingType = SqlOrderingType.Blocked;
+                SqlAlias alias = new SqlAlias(innerSelect);
+                this.currentSelect.From = new SqlJoin(SqlJoinType.OuterApply, this.currentSelect.From, alias, null, ss.SourceExpression);
+                return new SqlColumnRef(innerSelect.Row.Columns[0]);
+            }
+
+            internal override SqlSelect VisitSelect(SqlSelect select) {
+                SqlSelect save = this.currentSelect;
+                try {
+                    this.currentSelect = select;
+                    return base.VisitSelect(select);
+                }
+                finally {
+                    this.currentSelect = save;
+                }
+            }
+        }
+    }
+}