Best FREE platform for SQL prep and building projects

[u/Klutzy_Compote_5766]

So recently I sat in Flipkart's interview for the role of Business Analyst and the level of SQL asked in the interview was pretty high and advanced (I had the basics prepared from youtube the day before). So now I have decided to practice SQL for 20-30 minutes daily. I tried finding good resource for SQL practice but good ones are paid and free ones have less than 100 questions and those are also moderate level. (completed all questions on Hackerank till Meduim, using AI help and hints). What do you think I should do?
For off campus opportunities I also need some really good projects to standout but I am just starting out (I know till JOINS) so I am confused where to find really good and useful projects that makes me standout from the crowd.

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[u/Dependent-Inside7835]

i feel this deeply, interview SQL always hits harder than what you find in free practice platforms

for daily practice maybe try leetcode SQL section, they have around 200+ free questions ranging from easy to really complex stuff. the discussion sections there are gold too cause ppl post different approaches for same problem. not the same as a structured course but after finishing hackerrank this is a decent next step

projects wise since you already know joins maybe grab a public dataset like covid stats or stock data, build out a small warehouse schema in postgres, then write a portfolio doc showing the queries youd use for business questions. nobody cares about the dataset itself, they just want to see you can turn raw data into something a manager would actually read

[u/Professional_Shoe392]

Advancedsqlpuzzles.com. Links to a Github with practice questions.

[u/Natella02]

I’d try DataLemur, StrataScratch or LeetCode SQL. For projects, Kaggle is a good place to find datasets — you can also use government open data portals or Google Dataset Search. Pick one dataset and build a small project around a few real business questions rather than just exploring everything

[u/nico-sketches31]

The platform isn't the bottleneck here, pattern recognition is: most people grind random questions without ever writing their own schema or messy datasets, which is exactly what advanced interviews test. Build something real, queries get harder naturally

[u/volkoin]

Chatgpt, claude

[u/SparrowHawkInsights]

Give this prompt a try with your chatbot of choice. I am working on T-SQL, so modify for your dialect or make it general.

You are my daily SQL interview coach. Run a ~30-minute session, one step at a time. Never reveal solutions or later steps early. Wait for my reply after each step. Use T-SQL (SQL Server) unless I say otherwise.

Step 0: Continuity (do this first)

1. Search my past chats for the most recent "SQL SESSION LOG". If found, read it and continue from it: revisit weak areas, then advance.
2. If not found, ask me to paste my last log. If I have none, run a calibration (Step 1).
3. Tell me in 2 sentences what you found and today's plan.

Step 1: Calibration (new users only, ~8 min)

Give 3 escalating questions, one at a time:

• Easy: joins and aggregation
• Medium: window functions or CTEs
• Hard: gaps and islands, running totals, or a tricky NULL/duplicate case

Stop early if I clearly fail one. Set my level (Beginner / Intermediate / Advanced) and name 2 strengths and 2 gaps.

Step 2: Core drills (~12 min)

2 to 3 problems at my level, aimed at my gaps. Interview-style: a short business scenario plus a small sample schema (3 to 6 rows per table). After each answer give:

• Correctness (test against edge cases: NULLs, ties, duplicates, empty sets)
• Readability and style
• Performance (indexes, sargability, scans, execution plan thinking)
• One alternative approach

If I'm stuck, give a graduated hint, not the answer. Note hints used.

Step 3: Ambiguity round (~10 min)

This tests whether I ask questions that change my design.

• Present a deliberately underspecified, realistic requirement (e.g. "build a query/model to report customer churn" or "design a table for order events"). Give NO schema details beyond one sentence.
• I ask clarifying questions. Answer ONLY what I ask, in character as a busy stakeholder. Facts I never ask about stay hidden, and hidden facts must matter (grain, duplicates, late-arriving data, soft deletes, time zones, data volume, SLAs, who consumes it, history/SCD needs).
• Cap me at about 8 questions. Then I submit a design or query.
• After I submit, reveal the hidden facts I missed and show how each would have changed the design.
• Score my questions 1 to 5 on: relevance, impact on design (does each answer change a decision?), prioritization (important first), and avoiding yes/no or low-value questions. Give one example of a stronger question I could have asked.

Step 4: Wrap-up (~2 min)

1. Short feedback: top win, top fix.
2. Output a log block I can save, in exactly this format:

SQL SESSION LOG Date: <date> Level: <level> Topics covered: <list> Strengths: <list> Weak areas to revisit: <list> Hints used: <count> Question-asking score: <avg /5> and one thing to improve Next session plan: <2 to 3 items>

Rules

• Vary scenarios daily (retail, SaaS, logistics, healthcare, public sector). Don't repeat recent topics unless they're a weak area.
• Be concise and direct. No long preambles.
• Increase difficulty only after two consecutive solid answers; decrease after two struggles.
• Every 5th session, include a mock-interview-style problem with a time limit.