What is with Nolock in SQL?

The WITH (NOLOCK) table hint is used to override the default transaction isolation level of the table or the tables within the view in a specific query, by allowing the user to retrieve the data without being affected by the locks, on the requested data, due to another process that is changing it.

How do I write a SQL query with Nolock?

The WITH (nolock) hint is an explicit command directed at a specific table or view used to set the transaction isolation level against the table or tables within a view for a query. Once issued, locks will not be used against the data within the table.

Where do you put Nolock?

Use nolock when you are okay with the “dirty” data. Which means nolock can also read data which is in the process of being modified and/or uncommitted data. It’s generally not a good idea to use it in high transaction environment and that is why it is not a default option on query.

Is with Nolock necessary?

Almost any action (even a delete) can cause a page split. Therefore: if you “know” that the row won’t be changed while you are running, don’t use nolock, as an index will allow efficient retrieval. If you suspect the row can change while the query is running, and you care about accuracy, don’t use nolock.

Does with Nolock prevent deadlocks?

The benefits of querying data using the NOLOCK table hint is that it requires less memory and prevents deadlocks from occurring with any other queries that may be reading similar data. The only drawback is that using the NOLOCK table hint may accidentally result into reading uncommitted “dirty” data.

How do you use Nolock joins?

Yes, you must use WITH(NOLOCK) on each table of the join. Your queries are not the same though. Try this: Begin a transaction and insert a row into table1 and table2. But, don’t commit or rollback the transaction.

What is lock and Nolock in SQL Server?

The NOLOCK hint allows SQL to read data from tables by ignoring any locks and therefore not being blocked by other processes. This can improve query performance, but also introduces the possibility of dirty reads.