DBMS Interview Questions and Answers
Question - 81 : - How can you get the alternate records from the table in the SQL?
Answer - 81 : -
If you want to fetch the odd numbers then the following query can be used:
SELECT EmpId from (SELECT rowno,EmpId from Emp) WHERE mod(rowno,2)=1;
If you want to fetch the even numbers, then the following query can be used:
SELECT EmpId from (SELECT rowno,EmpId from Emp) WHERE mod(rowno,2)=0;
Question - 82 : - What is a CLAUSE in terms of SQL?
Answer - 82 : - This is used with the SQL queries to fetch specific data as per the requirements on the basis of the conditions that are put in the SQL. This is very helpful in picking the selective records from the complete set of the records.
Question - 83 : - What is 3NF in the DBMS?
Answer - 83 : -
3NF is the Third Normal Form.
Any table is said to have in the 3NF if it satisfies the following 2 conditions:
- A table is in the 2NF.
- Each non-prime attribute of a table is said to be non-transitively dependent on every key of the table.
Answer - 84 : -
BCNF is the Boyce Codd Normal Form which is stricter than the 3NF.
Any table is said to have in the BCNF if it satisfies the following 2 conditions:
- A table is in the 3NF.
- For each of the functional dependency X->Y that exists, X is the super key of a table.
Answer - 85 : -
2NF is the Second Normal Form.
Any table is said to have in the 2NF if it satisfies the following 2 conditions:
- A table is in the 1NF.
- Each non-prime attribute of a table is said to be functionally dependent in totality on the primary key.
Answer - 86 : -
1NF is known as the First Normal Form.
This is the easiest form of the normalization process which states that the domain of an attribute should have only atomic values. The objective of this is to remove the duplicate columns that are present in the table.
Question - 87 : - What is a functional dependency in the DBMS?
Answer - 87 : -
This is basically a constraint which is useful in describing the relationship among the different attributes in a relation.
Example: If there is some relation ‘R1’ which has 2 attributes as Y and Z then the functional dependency among these 2 attributes can be shown as Y->Z which states that Z is functionally dependent on Y.
Question - 88 : - What is E-R model in the DBMS?
Answer - 88 : - E-R model is known as an Entity-Relationship model in the DBMS which is based on the concept of the Entities and the relationship that exists among these entities.
Question - 89 : - What integrity rules exist in the DBMS?
Answer - 89 : -
There are 2 major integrity rules that exist in the DBMS.
They are:
- Entity Integrity: This states a very important rule that value of a Primary key can never have a NULL value.
- Referential Integrity: This rule is related to the Foreign key which states that either the value of a Foreign key is a NULL value or it should be the primary key of any other relation.
Answer - 90 : -
There are 3 levels of data abstraction in the DBMS.
They include:
- Physical Level: This is the lowest level of the data abstraction which states how the data is stored in the database.
- Logical Level: This is the next level of the data abstraction which states the type of the data and the relationship among the data that is stored in the database.
- View Level: This is the highest level in the data abstraction which shows/states only a part of the database.