Which Transact-SQL batch should you use?

You administer a Microsoft SQL Server 2014 database that contains a table named OrderDetail.

You discover that the NCI_OrderDetail_CustomerID non-clustered index is fragmented. You need to reduce fragmentation. You need to achieve this goal without taking the index offline.

Which Transact-SQL batch should you use?
A . CREATE INDEX NCI_OrderDetail_CustomerID ON OrderDetail.CustomerID WITH DROP EXISTING
B . ALTER INDEX NCI_OrderDetail_CustomerID ON OrderDetail.CustomerID REORGANIZE
C . ALTER INDEX ALL ON OrderDetail REBUILD
D . ALTER INDEX NCI_OrderDetail_CustomerID ON OrderDetail.CustomerID REBUILD

Answer: B

Explanation:

REORGANIZE specifies to reorganize the index leaf level. The REORGANIZE operation is always performed online. This means long-term blocking table locks are not held and queries or updates to the underlying table can continue during the ALTER INDEX REORGANIZE transaction.

References:https://docs.microsoft.com/en-us/sql/t-sql/statements/alter-index-transact-sql