database transactions

In database, a transaction is a group of statements that are executed atomically.

Subtopics

• ACID (atomicity, consistency, isolation, durability)
• conflict serializability

In SQL

In SQL, we use begin and commit to start and end a transaction:

begin;
  -- A group of SQL statements;
commit;

For example, consider the following table: R(id: integer, name: varchar(8)). If we perform the following transaction:

begin;
  insert into R values (1, 'Adam');
  insert into R values (1, 'Smith');
commit;

We won’t add anything because of integrity constraint violation.

We can also explicitly use the rollback keyword to abort a transaction. For example:

begin transaction;
 
  ...
  
  if ... then
    rollback transaction;
  end
 
commit transaction;

Related

• transactional memory