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The transaction, commit and rollback concepts are key to the ACID property of databases. [1] A COMMIT statement in SQL ends a transaction within a relational database management system (RDBMS) and makes all changes visible to other users. The general format is to issue a BEGIN WORK (or BEGIN TRANSACTION, depending on the database vendor ...
SQL refers to Structured Query Language, a kind of language used to access, update and manipulate database. In SQL, ROLLBACK is a command that causes all data changes since the last START TRANSACTION or BEGIN to be discarded by the relational database management systems (RDBMS), so that the state of the data is "rolled back" to the way it was before those changes were made.
A database transaction symbolizes a unit of work, performed within a database management system (or similar system) against a database, that is treated in a coherent and reliable way independent of other transactions. A transaction generally represents any change in a database. Transactions in a database environment have two main purposes:
To enable transaction time in the example above, two more fields are added to the Person table: transaction_from and transaction_to. Here, transaction_from is the time a transaction was made, and transaction_to is the time that the transaction was superseded (which may be infinity if it has not yet been superseded).
Nonetheless, in systems such as Microsoft SQL Server, as well as connection technologies such as ODBC and Microsoft OLE DB, autocommit mode is the default for all statements that change data, in order to ensure that individual statements will conform to the ACID (atomicity-consistency-isolation-durability) properties of transactions.
The time when a transaction is valid can be called the transaction time-period. It is a technical timeline controlled by a integration layer (for example a data warehouse ). [ 1 ] More formally, it is the point-in-time during which a fact stored in the database is considered to be true.
It is also possible to keep a separate journal of all modifications to a database management system. (sometimes called after images).This is not required for rollback of failed transactions but it is useful for updating the database management system in the event of a database failure, so some transaction-processing systems provide it.
The term "transaction" can have two different meanings, both of which might apply: in the realm of computers or database transactions it denotes an atomic change of state, whereas in the realm of business or finance, the term typically denotes an exchange of economic entities (as used by, e.g., Transaction Processing Performance Council or commercial transactions.