constraint is a rule which can not be voilated by end users.
Different types of constraints are available.They are:-
1)default constraint:-which is used to define a default
2)primary key:-the key which does not allows duplication
and null values.
3)foreign key:-the key used to refer primary key defined
field in another table and it allows duplication.
4)null:-which allows NULL values.
5)not null:-which does not allows NULL values.
6)unique key:-which does not allows duplication but allows
Constraints are the constraints which can provide on the
column data.The types of constraints are
1).Domain Integrity constraints
2).Entity Integrity constraints
3).Referential Integrity constraints
Constraints are used to restrict or protect the data and
accessing from the table
There are 5 types of constraints available,
1.Primary-which is not allowed duplication and Null values
2.Unique-Which is also Not allowed duplication But It is
allowed one single null values
3.Foreign - Which is allowed duplication and Null values.
But It refers Value from primary Key table to its own table
Constraints enable the RDBMS enforce the integrity of the
database automatically, without needing you to create
triggers, rule or defaults.
Types of constraints:
• PRIMARY KEY
• FOREIGN KEY
• NOT NULL
A PRIMARY KEY constraint is a unique identifier for a row
within a database table. Every table should have a primary
key constraint to uniquely identify each row and only one
primary key constraint can be created for each table. The
primary key constraints are used to enforce entity
integrity. ( Entity integrity is an integrity rule which
states that every table must have a primary key and that
the column or columns chosen to be the primary key should
be unique and not null)
A UNIQUE constraint enforces the uniqueness of the values
in a set of columns, so no duplicate values are entered.
The unique key constraints are used to enforce entity
integrity as the primary key constraints.
A FOREIGN KEY constraint prevents any actions that would
destroy link between tables with the corresponding data
values. A foreign key in one table points to a primary key
in another table. Foreign keys prevent actions that would
leave rows with foreign key values when there are no
primary keys with that value. The foreign key constraints
are used to enforce referential integrity.
A CHECK constraint is used to limit the values that can be
placed in a column. The check constraints are used to
enforce domain integrity.
A NOT NULL constraint enforces that the column will not
accept null values. The not null constraints are used to
enforce domain integrity, as the check constraints.
constraint define rules that must be followed to maintain
consistency and correctness of data.a constraint can either
be created while creating a table or can be added later.
constraint can be divided into the following types:--
(1)primary key constraint.
(3)foreign key constraint.
I am using SQL Server 2005, I have some select and update
statements in my query with WHERE clause
I want to prevent these queries from SQL injection attacks.
What are the steps and precautions to be taken for SQL
Does anybody have suggestions?
Thanks in advance,