What Is a Transaction?

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A transaction is a series of operations that are performed as one logical unit of work. Transactions allow SQL Server to ensure a certain level of data integrity and data recoverability. The transaction log, which every database must have, keeps a record of all transactions that make any type of modification (insert, update, or delete) to the database. SQL Server uses this transaction log to recover data in case of errors or system failures.

The integrity of a transaction depends in part on the SQL programmer. The programmer must know when to start and end the transaction and in what sequence to make data modifications to ensure logical consistency and meaningfulness of data. We'll cover how to begin and end transactions in later sections. Now that you know what a transaction is, let's take a look at the properties required for a valid transaction.