Yanlış: One of the most common online recommendations for curing this type of deadlock is to use a NOLOCK table hint in the SELECT statement, to prevent it from acquiring shared locks. This is bad advice. While it might prevent the deadlock, it can have unwanted side effects, such as allowing operations to read uncommitted changes to the database data, and so return inaccurate results. Doğru: The correct fix for this type of deadlock is to change the definition of the non-clustered index so that it contains, either as additional key columns or as INCLUDE columns, all the columns it needs to cover the query. Columns returned by the query that are not used in a JOIN, WHERE, or GROUP BY clause, can be added to the index as INCLUDE columns. Any column used in a JOIN, the WHERE clause, or in a GROUP BY should ideally be a part of the index key but, in circumstances where this exceeds the 900-byte limit, addition as an INCLUDE column may work as well. Implementing the covering index will resolve the deadlock without the unexpected side effects of using NOLOCK.
