Types of Integrity Constraints
There are four types of integrity constraints which are:
- Domain Constraints
- Entity integrity Constraints
- Key Constraints
- Referential integrity constraints
Domain Constraints
These are defined as the defination of valid set of values for an atribute. The data type of domain include string, char, time, integer, date, currency etc. The value of the attribute must be avialable in comparable domains.
Example:
|
Student_Id |
Name |
Semester |
Age |
|---|---|---|---|
|
21CSE100 |
Ramesh |
5th |
20 |
|
21CSE101 |
Kamlesh |
5th |
21 |
|
21CSE102 |
Aakash |
5th |
22 |
|
21CSE103 |
Mukesh |
5th |
20 |
Entity Integrity Constraints
Entity integrity constraints state that primary key can never contain null value because primary key is used to determine individual rows in a relation uniquely, if primary key contains null value then we cannot identify those rows. A table can contain null value in it except primary key field.
Example:
It is not allowed because it is containing primary key as NULL value.
|
Student_id |
Name |
Semester |
Age |
|---|---|---|---|
|
21CSE101 |
Ramesh |
5th |
20 |
|
21CSE102 |
Kamlesh |
5th |
21 |
|
21CSE103 |
Aakash |
5th |
22 |
|
Mukesh |
5th |
20 |
Key Constraints
Keys are the entity set that are used to identify an entity within its entity set uniquely. An entity set can contain multiple keys, bit out of them one key will be primary key. A primary key is always unique, it does not contain any null value in table.
Example:
|
Student_id |
Name |
Semester |
Age |
|---|---|---|---|
|
21CSE101 |
Ramesh |
5th |
20 |
|
21CSE102 |
Kamlesh |
5th |
21 |
|
21CSE103 |
Aakash |
5th |
22 |
|
21CSE102 |
Mukesh |
5th |
20 |
It is now acceptable because all rows must be unique.
Referential integrity constraints
It can be specified between two tables. In case of referential integrity constraints, if a Foreign key in Table 1 refers to Primary key of Table 2 then every value of the Foreign key in Table 1 must be null or avialable in Table 2.
Example:
Here, in below example Block_No 22 entry is not allowed because it is not present in 2nd table.
|
Student_id |
Name |
Semester |
Block_No |
|---|---|---|---|
|
22CSE101 |
Ramesh |
5th |
20 |
|
21CSE105 |
Kamlesh |
6th |
21 |
|
22CSE102 |
Aakash |
5th |
20 |
|
23CSE106 |
Mukesh |
2nd |
22 |
|
Block_No |
Block Location |
|---|---|
|
20 |
Chandigarh |
|
21 |
Punjab |
|
25 |
Delhi |
DBMS Integrity Constraints
Integrity constraints are the set of predefined rules that are used to maintain the quality of information. Integrity constraints ensure that the data insertion, data updating, data deleting and other processes have to be performed in such a way that the data integrity is not affected. They act as guidelines ensuring that data in the database remain accurate and consistent. So, integrity constraints are used to protect databases. The various types of integrity constraints are
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