2. SQL Interview Questions and Answers
Relational Database Management System (RDBMS) is a digital database management system in which the data is based on the relational model. It is the most common form of database that is used to date, and it has the system of using Structured Query Language (SQL) for querying purposes and for the maintenance of the database.
SQL, which is pronounced as sequel, is a domain-specific language that is used in the programming and is used to manage the data that is held within an RDBMS. Its field of expertise is to handle data that has a relation among entities and variables.
SQL offers few advantages over the traditional APIs, and these are:
- SQL allows accessing several records using a single command
- it helps in eliminating the need to reach a record
If you’ve been selected for the interview for SQL Developer, then you can brush up your SQL skills and knowledge by going through these top 20 questions that are asked during an interview. DinoSoftLab, with this blog, is aiming to help the budding/expert SQL developers prepare for their interview and bag the job that they deserve.
Here are the top 20 basic PL/SQL Interview Questions and Answers:
Question 1. What is DBMS?
DBMS stands for Database Management System that is used for controlling the creation, maintenance, and use of a database. DBMS is also termed as a file manager, which helps in managing the database instead of saving the files in the system.
Question 2. What is RDBMS?
The Relational Database Management System stores the data as a collection of tables. These tables have common fields between the columns of the table, which also provides relational operators for manipulating the data stored in the tables.
Question 3. What is SQL?
SQL is known as the Structured Query Language, which is used for forming a communication with the database. SQL is pronounced as sequel, and it is a standard language that is used to perform tasks like retrieval, updation, insertion, and deletion from the database.
Question 4. What is the significant difference between DBMS and RDBMS?
The significant difference between Database Management System and Relational Database Management System is that RDBMS stores data in the form of tables. These tables can be found having relations in their common fields.
Question 5. What are the tables and fields?
Tables are a set of data that has columns and rows which are organized in a model. The tables have a specific number of columns, which are called the fields, and it can have many rows, which are called records.
E.g., Table: Employee
Field: Emp ID, Emp Name, Date of Birth
Question 6. What is the significant difference between SQL and MySQL?
SQL is the standard language that is used for retrieving and manipulating structured databases, while MySQL is the relational database management system like SQL Server, which is used to manage SQL databases.
Question 7. What are the different constraints in SQL?
Constraints are the terms that are used to specify the rules related to the data that is present in the table. These constraints can be applied for single or multiple fields in an SQL table using the ALTER TABLE command.
These constraints are:
- NOT NULL- NULL value can’t be entered in the columns
- CHECK- It verifies if the values in fields satisfy the condition or not.
- DEFAULT- Assigns a default value on its own if no value is specified for the field.
- UNIQUE- Ensure unique value for the fields.
- INDEX- Helps in faster retrieval of records.
- FOREIGN KEY- Confirms the referential integrity of a record in another table.
- PRIMARY KEY- Identifies each record in a table.
Question 8. What is a Foreign Key?
It is used to form a relationship between two tables where the foreign key is referred to as the primary key of another table.
Question 9. What is a Primary Key?
The primary key is a special kind of key that has an implicit NOT NULL constraint, which means that the value of a primary key can never be NULL.
Question 10. What is a join in SQL?
Join is a keyword that is used to reach more data from the tables, having a relationship within their fields. During the usage of JOINs, keys play an important role.
Question 11. What are the different types of join? Explain.
Different types of joins can be used for the retrieval of data from the tables. These are:
- Inner Join– This joins returns rows when there is one or more match of rows between the tables.
- Right Join– The join returns rows from the right side of the table.
- Left Join– This join returns rows from the left side of the table.
- Full Join– This returns rows when there is a match of rows in any of the tables, i.e., it returns all the matching rows from the left and right side of the table.
Question 12. What is a Cross Join?
Cross Joins are the cartesian products of two tables that are included in the join. The resulting table will contain the same number of rows as the cross-product of the rows in the tables.
Question 13. What do you mean by Normalization?
The process of organizing fields and tables of a database to reduce the redundancy and dependency is known as Normalization. The goal of this process is to add, delete, or modify the field that can be changed into a single table.
Question 14. What is Denormalization?
DeNormalization is the process of accessing data from the higher to lower forms of the database. This process is used to introduce redundancy in the table by incorporating data from those tables that are related.
Question 15. What are the subsets of SQL?
There are three significant subsets in the SQL.
- Data Definition Language
- Data Manipulation Language
- Data Control Language
Question 16. What is Data Definition Language (DDL)?
DDL is a part of the database that defines the structure of the database in the initial stages when the database is to be created. It contains the commands: CREATE, DELETE, ALTER.
Question 17. What is Data Manipulation Language (DML)?
DML helps the user to access, retrieve, and manipulate the data by performing various operations.
- INSERT command for inserting data in the database.
- SELECT command for retrieving data from the database.
- UPDATE command to update data in the database.
- DELETE command to delete data from database.
Question 18. What is Data Control Language (DCL)?
DCL allows the user to control access to the database. DCL decides what part of the database will be accessed by which user at a given point of time. It is possible using commands GRANT and REVOKE.
GRANT: it allows a specific user to perform a task.
REVOKE: it is used to cancel any previously granted or denied permission.
Question 19. What is an SQL server?
The SQL Server is a database server with the primary function of storing and retrieving data as requested. Microsoft SQL Server is a software application developed by Microsoft, which helps in recovering data when other software applications required for the data running on the same or different computer on a network.
Question 20. What is Query?
The request for data or information from a table or combination of tables is known as a query. The query can be either a select query or an action query.
PL/SQL Queries Interview Question
These PL/SQL Queries Interview Questions and Answers will be enough to help you to prepare the basics for the interview that you have lined up and can help you get your dream job. The list of questions will be updated as we bring more SQL questions and answers for you.
If you are preparing for jQuery, we have a set of jquery questions that you can refer to.