Constraint are the rules enforced on data columns on table.

Five type of constraints 
Primary key
Unique Key
Foreign Key
Not Null
Check

Constraints are used to limit the type of data that can go 
into a table.

NOT NULL 
UNIQUE 
PRIMARY KEY 
FOREIGN KEY 
CHECK 
DEFAULT

Constraint are the rules enforced on data columns on table

types of constraints:

PRIMARYKEY
FOREIGN KEY 
NOT NULL
UNIQUE KEY
CHECK 
DEFAULT
Check

Constraints are the way by Databse managing the data inegrity.

Types of constraint are:-
1)NOT Null
2)Default
3)Check
4)Rule
5)Primary
6)Unique
7)Foreign

Constraints are used to limit the type of data that can go 
into a table.
 two basic types of constraints are there 
1.column level
2.table level
the difference is that column level constraints are apply
only to one column where as table level constraints are
apply to whole table 
Constraints are declare at the time of table creation using
CREATE TABLE command 

there are 6 constraints used in oracle
1.NOT NULL
2.UNIQUE
3.PRIMARY KEY
4.CHECK
5.DEFAULT
6.REFERENCES

Constraint are used to  table columns validations.
there are some constraints.

Primary key,
Foreign Key,
Not Null,
Check,
Unique Key,
default

constraints are the rules enforced on data columns on a 
table
 use:constraints are used to limit the type of data that 
can go in to a table

there are some constraints
a primarykey constraint
a unquekey constraint
a foreinkey constraint
a check constraint 
a not null constraint
a default constraint