A transaction is a related set of SQL queries treated as a single atomic unit. It can be either entirely committed or entirely rolled back.
The standard SQL way to express a transaction is
start transaction; # do work commit;
but there are many equivalent ways to get the same effect.
ACID stands for Atomicity, Consistency, Isolation, and Durability. You should understand what these terms mean or other geeks will refuse to talk to you.
In order from strongest to weakest, the transaction isolation levels are serializable, repeatable read, read committed, and read uncommitted. The InnoDB default is repeatable read.
