DBMS Basics - Interview Questions & Answers
1. What is DBMS?
The database management system is a collection of programs that enables user to store, retrieve, update and delete information from a database.
2. What is RDBMS?
Relational Data Base Management Systems (RDBMS) are database management systems that maintain data records and indices in tables. Relationships may be created and maintained across and among the data and tables. In a relational database, relationships between data items are expressed by means of tables. Interdependencies among these tables are expressed by data values rather than by pointers. This allows a high degree of data independence. An RDBMS has the capability to recombine the data items from different files, providing powerful tools for data usage.
3. What is a Database?
Database is nothing but an organized form of data for easy access, storing, retrieval and managing of data. This is also known as structured form of data which can be accessed in many ways.
4. What are tables and Fields?
A table is a set of data that are organized in a model with Columns and Rows. Columns can be categorized as vertical, and Rows are horizontal. A table has specified number of column called fields but can have any number of rows which is called record.
5. What are primary keys and foreign keys?
Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null. Due to their importance in relational databases, Primary keys are the most fundamental of all keys and constraints. A table can have only one Primary key. Foreign keys are both a method of ensuring data integrity and a manifestation of the relationship between tables.
6. How is the primary key different from a unique key?
Both the primary and unique keys uniquely identify a record in a database table. One difference is that you can have more than one unique key per table, but only one primary key. Also, the primary key does not allow any null value, while the unique key allows one.
7. What are the different type of SQL's statements?
Types of SQL statements are DDL, DML & DCL.

1. DDL – Data Definition Language
DDL is used to define the structure that holds the data. For example, Create, Alter, Drop and Truncate table.

2. DML– Data Manipulation Language
DML is used for manipulation of the data itself. Typical operations are Insert, Delete, Update and retrieving the data from the table. Select statement is considered as a limited version of DML, since it can't change data in the database. But it can perform operations on data retrieved from DBMS, before the results are returned to the calling function.

3. DCL– Data Control Language
DCL is used to control the visibility of data like granting database access and set privileges to create tables etc. Example - Grant, Revoke access permission to the user to access data in database.
8. What is a join?
This is a keyword used to query data from more tables based on the relationship between the fields of the tables. Keys play a major role when JOINs are used.
9. What are the types of join and explain each?
There are various types of join which can be used to retrieve data and it depends on the relationship between tables.

Inner join.
Inner join return rows when there is at least one match of rows between the tables.
Right Join.
Right join return rows which are common between the tables and all rows of Right hand side table. Simply, it returns all the rows from the right hand side table even though there are no matches in the left hand side table.
Left Join.
Left join return rows which are common between the tables and all rows of Left hand side table. Simply, it returns all the rows from Left hand side table even though there are no matches in the Right hand side table.
Full Join.
Full join return rows when there are matching rows in any one of the tables. This means, it returns all the rows from the left hand side table and all the rows from the right hand side table.
10. What is Normalization?
Database normalization is the process of organizing the attributes and tables of a relational database to minimize data redundancy.
Questions & Answers
Database Management (DBMS)