SQL Query Interview Questions

Last updated by on Dec 21, 2024 at 06:20 PM

| Reading Time: 3 minutes

To land your dream job as a data engineer, you need to master the Structured Query Language (SQL) interview questions. SQL is incredibly useful when youâ€™re dealing with large amounts of data, want to retrieve specific results, or draw insights quickly. No wonder that it is extremely popular among data scientists/engineers and anyone involved in data work.

Being skilled at SQL and excellent at answering SQL query interview questions is especially crucial if your dream job is to be a data engineer. This article will help you assess your SQL interview prep and clear some of the concepts.

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In this article, weâ€™ll learn:

SQL Query: Introduction and Usage

SQL is the most common language used to extract and organize data stored in a relational database. SQL allows you to:

Execute queries
Retrieve data
Insert, update, and delete data
Create new databases, tables, views, and stored procedures
Set access permissions and more!

Letâ€™s jump right in and look at some sample SQL/SQL query-related interview questions and answers to see its use in action.

SQL Query Interview Questions and Answers for Practice

Which TCP/IP port does the SQL Server run?
While TCP/IP of an SQL server can be changed, by default, it runs on port number 1433.
What is the order of clauses in an SQL SELECT statement?
The order goes: SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY. Here, everything other than SELECT and FROM is optional. Only SELECT and FROM are mandatory.
How would you select random rows from a table?
We can select random rows in SQL using a SAMPLE clause as follows:

SELECT * FROM table_name SAMPLE(5);

How will you rename a column in the output of the SQL query?
To rename a column in the output of an SQL query, we can make use of the AS keyword as follows:

SELECT old_column_name AS new_column_came FROM table_name;

SQL Query Interview Questions Based on a Sample Data Table

Hereâ€™s a sample table: Employee

Weâ€™ll now look at some sample SQL query questions and answers:

Write an SQL query that gets the first two characters of last_name from the Employee table.

Select substring(last_name,1,2) from Employee;

Write an SQL query that gets the department from the Employee table after replacing â€˜eâ€™ with â€˜Z.â€™

Select REPLACE(department,’e’,’Z’) from Employee;

Write an SQL query that gets the first and last names from the Employee table together separated by a space in a single column full_name.

Select CONCAT(first_name, ‘ ‘, last_name) AS ‘full_name’ from Employee;

There can be numerous questions that can be made by changing constraints and requirements. Some common constraints and requirements include:

Printing a column after removing white spaces from the left or right side.
Getting unique values only from a column and avoiding duplicates
Printing in ascending or descending order
Print all details associated with a specific employeeID, name, etc.
Print all details associated with an employeeID, name, etc. that starts or ends with a given character
Print the names of employees with IDs/salaries within a specified range.

SQL Interview Question FAQs

1. What are the different types of statements supported by SQL?

There are three types of statements supported by SQL â€” Data Definition Language (DDL), Data Manipulation Language (DML), and Data Control Language (DCL).

2. What is the difference between DDL, DML, and DCL in SQL?

Data Definition Language statements are used to define the database structures like tables. Example of DDL statements: CREATE, ALTER, and DROP. Data Manipulation Language statements are used to manipulate the data stored in the records. Example of DML statements: INSERT, UPDATE, and DELETE. (SELECT is a partial DML statement). Data Control Language statements are used to set privileges that give, revoke, or limit access to databases for specific users. Example of DCL statements: GRANT, REVOKE.

3. How do we use the DISTINCT statement in SQL? What is its use?

The DISTINCT statement is used along with the SELECT statement. If there are duplicate values in the record, the DISTINCT statement is used to select only all unique values from the record to avoid duplicates.

4. What are the different Clauses used in SQL?

The different clauses used in SQL are: WHERE, GROUP BY, HAVING, ORDER BY, and USING.

5. Why do we use SQL constraints? Which constraints can we use while creating a database in SQL?

Constraints set the rules for all the records in the table, so any action that violates the constraints is aborted. Constraints can be declared at the time of table creation using CREATE TABLE or later using ALTER TABLE.

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