The read committed isolation level defines that a transaction can't read data that is not committed by other transactions. This means that the dirty read is no longer an issue, but other issues may occur.

Let's see the following diagram:

In this example, Transaction A reads some data. Then, Transaction B writes that same data and commits. Later, Transaction A reads that same data again and may get different values, because Transaction B already made changes to that data and committed. This is a non-repeatable read.

Note that READ_COMMITTED can also create issues like phantom reads. A phantom reads occurs when a transaction isolation is selected as REPEATABLE_READ.

Let's see the REPEATABLE_READ isolation level in detail.