Which one of the following database concurrency issues occurs when one transaction reads information that was written to a database by a second transaction that never committed?

Dirty reads occur when one transaction reads a value from a database that was written by another transaction that did not commit. Lost updates occur when one transaction writes a value to the database that overwrites a value needed by transactions that have earlier precedence, causing those transactions to read an incorrect value. Incorrect summaries occur when one transaction is using an aggregate function to summarize data stored in a database, while a second transaction is making modifications to the database, causing the summary to include incorrect information. SQL injection is a web application security flaw, not a database concurrency problem.