PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

314 Chapter 13 Advanced MySQL Programming
A transaction that has been permanently written to the database is said to be committed.A
transaction that is not written to the database—so that the database is reset to the state it
was in before the transaction began—is said to be rolled back.
Using Transactions with InnoDB
By default, MySQL runs in autocommit mode.This means that each statement you execute
is immediately written to the database (committed). If you are using a transactionsafe
table type, more than likely you don’t want this behavior.
To turn autocommit off in the current session, type
set autocommit=0;
If autocommit is on, you need to begin a transaction with the statement
start transaction;
If it is off, you do not need this command because a transaction will be started automatically
for you when you enter an SQL statement.
After you have finished entering the statements that make up a transaction, you can
commit it to the database by simply typing
commit;
If you have changed your mind, you can revert to the previous state of the database by
typing
rollback;
Until you have committed a transaction, it will not be visible to other users or in other
sessions.
Let’s look at an example. Execute the ALTER TABLE statements in the previous section
of the chapter on your books database, as follows, if you have not already done so:
alter table orders type=innodb;
alter table order_items type=innodb;
These statements convert two of the tables to InnoDB tables. (You can convert them
back later if you want by running the same statement but with type=MyISAM.)
Now open two connections to the books database. In one connection, add a new
order record to the database:
insert into orders values (5, 2, 69.98, '2008-06-18');
insert into order_items values (5, '0-672-31697-8', 1);
Now check that you can see the new order:
select * from orders where orderid=5;