Local and Global Constraints
Constraints and Triggers
A constraint is a relationship among data
elements that the DBMS is required to
Example: key constraints.
Triggers are only executed when a
Transactions, Views, Indexes
Controlling Concurrent Behavior
Virtual and Materialized Views
Speeding Accesses to Data
Database systems are normally being
accessed by many users or processes
at the same time.
Both queries and modificati
Introduction to SQL
SQL is a very-high-level language.
Say what to do rather than how to do it.
Avoid a lot of data-manipulation details
needed in procedural languages like C+ or
Algebra of Bags
What is an Algebra
Mathematical system consisting of:
Operands - variables or values from which
new values can be constructed.
Operators - symbols denoting procedures
that construct new values from gi
Extended Relational Algebra
The Extended Algebra
= eliminate duplicates from bags.
= sort tuples.
= grouping and aggregation.
Outerjoin : avoids dangling tuples = tuples
that do not join wi