You use a Microsoft SQL Server 2012 database that contains two tables named SalesOrderHeader and SalesOrderDetail. The indexes on the tables are as shown in the exhibit. (Click the Exhibit button.)



You write the following Transact-SQL query:



You discover that the performance of the query is slow. Analysis of the query plan shows table scans where the estimated rows do not match the actual rows for SalesOrderHeader by using an unexpected index on SalesOrderDetail.

You need to improve the performance of the query.

What should you do?

A. Use a FORCESCAN hint in the query.

B. Add a clustered index on SalesOrderId in SalesOrderHeader.

C. Use a FORCESEEK hint in the query.

D. Update statistics on SalesOrderId on both tables.

Explanation:

New statistics would be useful.

The UPDATE STATISTICS command updates query optimization statistics on a table or indexed view. By default, the query optimizer already updates statistics as necessary to improve the query plan; in some cases you can improve query performance by using UPDATE STATISTICS or the stored procedure sp_updatestats to update statistics more frequently than the default updates.

References: http://msdn.microsoft.com/en-us/library/ms187348.aspx