Update MultithreadedOrderInsertMain.cs

There is a bug in the code when it tries to append the union, it generates invalid SQL. By encapsulating the underlying select's into parens, it eliminates the issue in both cases (just the first query vs both queries unioned).

Author: chadbaldwin

samples/databases/wide-world-importers/workload-drivers/order-insert/MultithreadedOrderInsert/MultithreadedOrderInsertMain.cs

@@ -151,10 +151,10 @@ public void PerformSqlTask(int TaskNumber, MultithreadedOrderInsertMain ParentFo
                             var orderTable = new DataTable("Orders");
                             da.Fill(orderTable);
 
-                            selectCommand.CommandText = "SELECT TOP(7) 1 AS OrderReference, si.StockItemID, si.StockItemName AS [Description], FLOOR(RAND() * 10) + 1 AS Quantity FROM Warehouse.StockItems AS si WHERE IsChillerStock = 0 ORDER BY NEWID()";
+                            selectCommand.CommandText = "SELECT * FROM (SELECT TOP(7) 1 AS OrderReference, si.StockItemID, si.StockItemName AS [Description], FLOOR(RAND() * 10) + 1 AS Quantity FROM Warehouse.StockItems AS si WHERE IsChillerStock = 0 ORDER BY NEWID()) x";
                             if (rnd.Next(1, 100) < 4)
                             {
-                                selectCommand.CommandText += "UNION ALL SELECT TOP(1) 1 AS OrderReference, si.StockItemID, si.StockItemName AS [Description], FLOOR(RAND() * 10) + 1 AS Quantity FROM Warehouse.StockItems AS si WHERE IsChillerStock <> 0 ORDER BY NEWID()";
+                                selectCommand.CommandText += " UNION ALL SELECT * FROM (SELECT TOP(1) 1 AS OrderReference, si.StockItemID, si.StockItemName AS [Description], FLOOR(RAND() * 10) + 1 AS Quantity FROM Warehouse.StockItems AS si WHERE IsChillerStock <> 0 ORDER BY NEWID()) x";
                             }
                             selectCommand.CommandText += ";";
                             var orderLinesTable = new DataTable("OrderLines");