Berkeley DB and InnoDB. 

Automicity  transactions are atomic and should be treated 
as one in case of rollback. Consistency - the database 
should be in consistent state between multiple states in 
transaction.

Isolation  no other queries can access the data modified by 
a running transaction. Durability system crashes should not 
lose the data. 

A set of instructions/queries that should be executed or 
rolled back as a single atomic unit. 

Each row has two additional columns associated with it - 
creation time and deletion time, but instead of storing 
timestamps, MySQL stores version numbers

Multiversion concurrency control (abbreviated MCC or MVCC),
in the database field of computer science, is a concurrency
control method commonly used by database management systems
to provide concurrent access to the database.
MVCC provides each user connected to the database with a
"snapshot" of the database for that person to work with. Any
changes made will not be seen by other users of the database
until the transaction has been committed.

Table-level locks allow the user to lock the entire table, 
page-level locks allow locking of certain portions of the 
tables row-level locks are the most granular and allow 
locking of specific rows. 

The front layer takes care of network connections and 
security authentications, the middle layer does the SQL 
query parsing, and then the query is handled off to the 
storage engine.

A storage engine could be either a default one supplied 
with MySQL (MyISAM) or a commercial one supplied by a third-
party vendor (ScaleDB, InnoDB, etc.) 

Prior to MySQL 5.0.3: those are all synonyms. After MySQL 
5.0.3: BIT data type can store 8 bytes of data and should 
be used for binary data. 

FLOATs store floating point numbers with 8 place accuracy 
and take up 4 bytes.
DOUBLEs store floating point numbers with 16 place accuracy 
and take up 8 bytes.
REAL is a synonym of FLOAT for now.

999.99 to -99.99. Note that with the negative number the 
minus sign is considered one of the digits. 

That field gets the current timestamp whenever the row gets 
altered.

Create two columns of type TIMESTAMP and use the second one 
for your real data. 

The column exhibits the same behavior as a single timestamp 
column in a table with no other timestamp columns. 

TIMESTAMP DEFAULT :- when new row get inserted or existing
row get updated that time current timestamp get inserted.

CURRENT_TIMESTAMP :- when row get inserted that time current
timestamp get inserted. No change on update.

ON UPDATE CURRENT_TIMESTAMP :- when row get updated that
time current timestamp get inserted. On inserted default
value get  inserted

On initialization places a zero in that column, on future 
updates puts the current value of the timestamp in. 

A default value is used on initialization, a current 
timestamp is inserted on update of the row.