Top 50 SQL Interview Questions With Answers

Here are some of the most frequently asked SQL interview questions along with their solutions:

SQL Query Examples:

Fetch “FIRST_NAME” from Worker table with alias “WORKER_NAME”:
```
SELECT FIRST_NAME AS WORKER_NAME FROM Worker; 
```

2. Fetch “FIRST_NAME” in uppercase:

SELECT UPPER(FIRST_NAME) FROM Worker;

3. Fetch unique DEPARTMENT values:

SELECT DISTINCT DEPARTMENT FROM Worker;

4. Print first three characters of FIRST_NAME:

SELECT SUBSTRING(FIRST_NAME, 1, 3) FROM Worker;

5. Find position of ‘b’ in ‘Amitabh’:

SELECT INSTR(FIRST_NAME, 'b') FROM Worker WHERE FIRST_NAME = 'Amitabh';

6. Remove right-side whitespace from FIRST_NAME:

SELECT RTRIM(FIRST_NAME) FROM Worker;

7. Remove left-side whitespace from DEPARTMENT:

SELECT LTRIM(DEPARTMENT) FROM Worker;

8. Print unique DEPARTMENT names and their lengths:

SELECT DISTINCT DEPARTMENT, LENGTH(DEPARTMENT) FROM Worker;

9. Replace ‘a’ with ‘A’ in FIRST_NAME:

SELECT REPLACE(FIRST_NAME, 'a', 'A') FROM Worker;

10. Combine FIRST_NAME and LAST_NAME into COMPLETE_NAME:

SELECT CONCAT(FIRST_NAME, ' ', LAST_NAME) AS COMPLETE_NAME FROM Worker;

You Should Know:

Essential SQL Commands for Practice

Create a table:

CREATE TABLE Worker ( 
WORKER_ID INT PRIMARY KEY, 
FIRST_NAME VARCHAR(50), 
LAST_NAME VARCHAR(50), 
DEPARTMENT VARCHAR(50) 
);

Insert data:

INSERT INTO Worker VALUES (1, 'Amitabh', 'Bachchan', 'Admin');

Update records:

UPDATE Worker SET DEPARTMENT = 'HR' WHERE FIRST_NAME = 'Vipul';

Delete records:

DELETE FROM Worker WHERE DEPARTMENT = 'Admin';

Filter with LIKE:

SELECT  FROM Worker WHERE DEPARTMENT LIKE 'Admin%';

Linux & Windows Commands for Database Management

Check MySQL service status (Linux):
```
sudo systemctl status mysql 
```
Start MySQL service (Windows):
```
net start mysql 
```

Backup a database (Linux/Windows):

mysqldump -u username -p database_name > backup.sql

Restore a database:

mysql -u username -p database_name < backup.sql

SQL Learning Resources

What Undercode Say

Mastering SQL is crucial for data engineering, cybersecurity, and backend development. These commands form the foundation for database manipulation, query optimization, and security testing. Practice these queries in real environments like MySQL, PostgreSQL, or SQLite. For penetration testers, SQL injection testing (' OR '1'='1) is a key skill—always sanitize inputs in web apps!

Expected Output:

A structured SQL cheat sheet with executable queries, database management commands, and verified learning resources.

Prediction

SQL will remain a fundamental skill in data engineering, with increasing demand for optimization and NoSQL integration in cloud databases like AWS RDS and DynamoDB.

References:

Reported By: Sachincw Top – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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