Use with (nolock) to improve query performance in suitable scenarios

The with (nolock) here refers to the with option in the SQL query, for example:

Select * from T1 with (nolock) where a = 'xx'

With (nolock) means that no locks are taken into account during query, and dirty reads may be performed. Although dirty reading may occur, it will improve the performance. It is used in some scenarios where dirty reading is not required. For example, when a user deletes all posts in the Forum when posting advertisements, this query will not be afraid of dirty reading or deleting all posts, it is not a problem to miss a sending task.

There are many options for with, such as specifying a lock table, locking rows, and using an index when specifying a query.

See http://msdn.microsoft.com/en-us/library/ms187373.aspx for details