Sequence of instructions to satisfy a query A transaction is a sequence of operations that must be executed together as a single, indivisible unit of work, in order to maintain the consistency of the data. Transactions ensure that either all the operations in the sequence are executed successfully, or none of them are executed at all. For example, most banking operations should be transactions: if an account is debited, another should be credited. The case where only one of those two operations happens is undesirable as it would either destroy or create money. Either both happen or none.