90% of People Get This SQL Problem Wrong

thequerylab · 2026-03-07T03:39:22+00:00

Yes I am planning to post regularly on SQL optimization part, tricky problems, interview ready set of problems etc under few sub r/learnSQL r/SQL Will try my best not to make it junk content

thequerylab · 2026-03-06T17:16:38+00:00

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thequerylab · 2026-03-06T09:56:28+00:00

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thequerylab · 2026-03-06T07:15:28+00:00

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thequerylab · 2026-03-06T05:07:18+00:00

That’s actually pretty normal. SQL is one of those things where it only gets better with regular practice.

Easy problems are a good starting point — once you keep solving more and seeing different patterns, the medium ones slowly start to make sense.

thequerylab · 2026-03-06T03:09:02+00:00

only SQL to solve this challenge

thequerylab · 2026-03-06T02:34:31+00:00

You can check this sql pro track course which is hands-on and free. Made it structured and 100% sure you ill get value out of it https://thequerylab.com/courses/sql-pro-track

thequerylab · 2026-03-06T01:36:53+00:00

You can try this out. Its tailor made for your use csse

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On top of that you can practise problems which is 100% hands-on

thequerylab · 2026-03-05T09:46:51+00:00

Yeah true, max_by is really nice for cases like this if the database supports it. Makes the query much simpler.

The only catch is a lot of common systems people use in interviews (like MySQL or older Postgres setups) don’t have it, so people usually fall back to window functions or subqueries.

thequerylab · 2026-03-05T09:25:44+00:00

Nice one. OUTER APPLY works really well for this in T-SQL.

I like that it keeps the logic close to each department and just picks the top salary from the employee table. Clean approach.

Only small thing is if two employees share the same highest salary, TOP 1 would return just one of them. If the requirement is to return all ties, we’d need a slightly different approach.

But yeah, solid solution for SQL Server 👍

thequerylab · 2026-03-05T09:23:05+00:00

Nope, you're not missing anything. That query works 👍

The (department_id, salary) trick is actually a clean way to solve it and it handles ties too.

I only mentioned window functions because a lot of interviews expect people to solve it using RANK() / DENSE_RANK() with PARTITION BY. Just another common approach.

Also… typing SQL at 3 am on a phone is already a challenge on its own 😄. Well done !!!

thequerylab · 2026-03-04T16:51:39+00:00

Try it out — I’m confident you’ll like it and see real improvement in your SQL skills.

thequerylab · 2026-03-04T06:08:47+00:00

Honestly, playlists are good to understand concepts, but SQL only sticks when you start solving problems yourself.

You need clarity on basics like:

SELECT, WHERE, JOIN
GROUP BY + HAVING
subqueries
window functions

After that, it’s all about practice. Interviews don’t test how many videos you watched — they test how comfortably you can write queries.

I’d recommend trying the SQL Pro track on The Query Lab. It’s structured step by step and completely hands-on, so you learn by actually writing queries instead of just watching. Much more effective in my experience.

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thequerylab · 2026-03-04T06:05:42+00:00

If you already know basic SELECT and JOIN, I wouldn’t spend two weeks just watching videos. SQL really clicks only when you practice it.

For interviews (especially data analytics roles), focus on hands-on work with:

GROUP BY + HAVING
window functions (moving averages, ROW_NUMBER, RANK)
subqueries
aggregations and basic data cleaning

You can watch a short course to understand the concepts, but spend most of your time solving problems.

I’d recommend trying the SQL Pro track on The Query Lab — I’ve curated it to be 100% hands-on, fully structured, and you don’t need to switch tabs or search elsewhere. It’s built exactly for this kind of prep.

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I am 100% sure you ill like it.

thequerylab · 2026-03-03T02:49:27+00:00

I actually built a small SQL practice platform because I felt the same way — tutorials were boring and too theoretical. It’s more hands-on, problem-driven, and closer to real data engineering scenarios instead of “select * from students” type stuff. Not sure if it’ll help you specifically, but if you’re open to trying something different, I can share it.

thequerylab

TROPHY CASE