#1. Your database contains two tables named DomesticSalesOrders and InternationalSalesOrders. Both tablescontain more than 100 million rows. Each table has a Primary Key column named SalesOrderId. The datain the two tables is distinct from one another. Business users want a report that includes aggregateinformation about the total number of global sales and total sales amounts. You need to ensure that yourquery executes in the minimum possible time. Which query should you use?
Explanation: http://msdn.microsoft.com/en-us/library/ms180026.aspx http://blog.sqlauthority.com/2009/03/11/sql-server-difference-between-union-vs-union-alloptimalperformance-comparison/