You administer a Microsoft SQL Server 2012 database named Orders.

Orders contains a table named OrderShip that is defined as follows:

A NULL value represents a domestic order. Ninety percent of the values in CountryCode are NULL.

Customers require a procedure that will return orders for all customers from a specified country.

You create a new procedure:



Performance on this procedure is slow.

You need to alter the schema to optimize this query. Objects created must use a minimum amount of resources.

Which Transact-SQL statement should you use?

A. CREATE NONCLUSTERED INDEX IX_CountryCode ON Ordership (CountryCode) WHERE CountryCode IS NOT NULL

B. CREATE STATISTICS ST_CountryCode ON OrderShip (CountryCode) WHERE CountryCodeIS NOT NULL

C. CREATE CLUSTERED INDEX IX_CountryCode ON OrderShip (CountryCode)

D. CREATE INDEX IX_CountryCode ON OrderShip (CustomerID) WHERE CountryCode IS NOT NULL

Explanation:

Here creating statistics is relevant. The CREATE STATISTICS command creates query optimization statistics on one or more columns of a table, an indexed view, or an external table. For most queries, the query optimizer already generates the necessary statistics for a high-quality query plan; in a few cases, you need to create additional statistics with CREATE STATISTICS or modify the query design to improve query performance.

References: https://docs.microsoft.com/en-us/sql/t-sql/statements/create-statistics-transact-sql