The MySQL default storage engine MyISAM does not support transactions. In 
this table type the developer of MySQL followed another paradigm for data 
integrity called  atomic operations , as shown in Example 1 2. Changes 
produced by individual statements are committed to the database 
immediately as soon as they execute. In other words, a 
COMMIT
 statement 
implicitly follows each statement. To ensure database integrity code has to be 
provided in the application if required. 
MySQL supports transactions with the InnoDB and BDB transactional storage 
engines. InnoDB provides full ACID compliance.
Example 1 2   Atomic operation
INSERT INTO table1 ... 
COMMIT
DELETE FROM table2 ... 
COMMIT
Referential integrity
Referential integrity ensures that relationships between tables remain 
consistent. When one table has a foreign key to another table, the concept of 
referential integrity states that it is not allowed to add a record to the table that 
contains the foreign key unless there is a corresponding record in the linked 
table. In MySQL Server, MyISAM tables do not support foreign key 
constraints. MySQL only parses the FOREIGN KEY syntax in 
CREATE TABLE
commands, but does not use or store this information. Only InnoDB tables 
support checking of foreign key constraints including 
ON DELETE CASCADE
 and 
ON UPDATE CASCADE
.
Views
A view is a definition for a  virtual table  (virtual because there is no 
permanent allocation of storage space) which is assembled at reference time 
from selected rows and columns of one or more real tables. 
Views are useful for two main reasons: 
  They enable users to see data, from a generalized database design, in the 
form most convenient for their needs. 
  They may be used to secure the database by restricting users to just that 
data they need to know.
MySQL does not support views.
Subqueries
Subqueries are nested queries in a SQL statement (Example 1 3). They are 
not supported in MySQL 4.0. 
 Chapter 1. Introduction 
37






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