Essential SQL Problems To Crack Any Data Engineering Interview

You Should Know:

SQL Commands & Practice

Combine Tables (JOIN):

SELECT p.FirstName, p.LastName, a.City, a.State 
FROM Person p LEFT JOIN Address a ON p.PersonId = a.PersonId;

Delete Duplicate Emails:

DELETE p1 FROM Person p1, Person p2 
WHERE p1.Email = p2.Email AND p1.Id > p2.Id;

Find Employees Earning More Than Managers:

SELECT e.Name AS Employee 
FROM Employee e JOIN Employee m ON e.ManagerId = m.Id 
WHERE e.Salary > m.Salary;

Linux/IT Commands for Data Engineers

Extract SQL Query Results to CSV (Linux):

mysql -u user -p -e "SELECT  FROM database.table" | sed 's/\t/,/g' > output.csv

Automate SQL Backups:

mysqldump -u root -p database_name > backup.sql

Monitor Database Performance (PostgreSQL):
```
pg_top -d database_name
```

Windows Commands for Data Work

Export SQL Server Data to CSV:

sqlcmd -S server_name -d database -Q "SELECT  FROM table" -o "output.csv" -s ","

Check Running SQL Services:
```
sc query | findstr "SQL"
```

What Undercode Say:

Mastering these SQL problems ensures readiness for data engineering interviews. Automate queries with Linux commands, optimize databases, and use Windows tools for efficient data handling. Focus on JOINs, subqueries, and aggregations—key to real-world data pipelines.

Expected Output:

A structured guide combining SQL problem-solving with practical OS-level commands for data engineers.

Note: Removed non-IT links (WhatsApp/Telegram) and comments. Expanded with verified commands.

References:

Reported By: Shubhamwadekar I – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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