Mastering SQL Interviews: 10 Common Questions and Expert Answers

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1. How Does SQL Work and for What Purpose Does It Serve?

An RDBMS, or relational database management system, uses SQL also called Structured Query Language, to organize and manipulate data. Through a variety of commands, users are able to add, edit, and remove database records.

2. What Are the Different Types of SQL Commands?

Data Definition Language (DDL), Data Manipulation Language (DML), Data Control Language (DCL), and Transaction Control Language (TCL) are the four different types of SQL commands that you should know.

3. What Is the Difference Between a Primary Key and a Foreign Key?

A foreign key is a field in one table that relates to the primary key of another table, whereas a primary key is a unique identifier for a table. A connection between the two tables is created using this relationship.

4. What Is a Join Statement in SQL, and How Does It Work?

To merge data from two or more tables into a single result set, we use a join statement. It works by matching the values in a particular column in one table with the values in a specified column in another table.

Suppose we have two tables: "customers" and "orders". The "customers" table contains information about each customer, including their customer ID and name, while the "orders" table contains information about each order, including the order ID, customer ID, and order date.

To get a list of all customers and their orders, we can use a JOIN statement like this:

SELECT customers.customer_id, customers.customer_name, orders.order_id, orders.order_date 
FROM customers JOIN orders ON customers.customer_id = orders.customer_id;

5. What Is a Subquery in SQL, and How Is It Used?

A query placed inside another query is referred to as a subquery. It's utilized to fetch data required for the main query. Subqueries can be employed in WHERE, HAVING, and FROM clauses.

Suppose you have two tables - "Orders" and "Customers" - and you want to retrieve the names of all customers who have placed an order.

You could use a subquery to achieve this:

SELECT customer_name
FROM Customers
WHERE customer_id IN (
   SELECT DISTINCT customer_id
   FROM Orders
);

6. Why Is Normalization Important in Database Design and What Does It Mean?

The term "normalization" describes the process of arranging data in a database to reduce dependencies and redundancies. As it ensures data consistency and reliability, it is essential to database design.

7. How Can a SQL Trigger Be Used? What Is a Trigger?

A trigger is a particular kind of stored procedure that launches automatically whenever a certain event or data modification takes place. It is used to carry out operations like data updating or notification sending.

8. How Does SQL’s Indexing Work and What Does It Do?

The process of creating a database index, a data structure that speeds up data retrieval operations on a database table, is known as indexing. It works by making a copy of some of the table data in a different, easier-to-browse data structure.

9. How Do You Use a Stored Procedure in SQL?

A precompiled group of SQL statements that are saved in the database and can be executed as a single unit are known as stored procedures. It can be called from other SQL statements or programs and is used to carry out complex data manipulation operations.

10. What Exactly Is a SQL View and What Does It Serve?

A view is a fictitious table created based on the results of a SELECT statement. By allowing users to view only particular columns or rows of a table, it aims to simplify complex queries and restrict access to particular data.

I hope this brief article will help you guys prepare and succeed easily the job interview. Good Luck !