What is a phantom read in SQL?

Can you explain what a phantom read is in SQL?

Sure! A phantom read occurs when a transaction reads a set of rows that match a certain condition, but another transaction inserts or deletes rows that affect that set before the first transaction is completed.

How does it differ from dirty reads and non-repeatable reads?

Great question! Dirty reads allow a transaction to read uncommitted changes from another transaction. Non-repeatable reads occur when a row is changed by another transaction after it has been read, while phantom reads involve new rows being added that match the original query.

What isolation level can prevent phantom reads?

To prevent phantom reads, you can use the Serializable isolation level. This level ensures that no new rows can be added that would match the query of a transaction until that transaction is complete.

Can you give an example of a phantom read scenario?

Certainly! Imagine a transaction that counts the number of active users. If another transaction adds a new user during the count, the first transaction might see a different count if it runs again, which is a phantom read.