How to Understand SQL Commands

Master SQL the Smart Way: The 20% That Delivers 80% of Results After years of working with SQL, I've realized something: You don't need to know EVERY SQL command to be highly effective. Here are the essential commands that handle most of your daily database tasks: Key Commands That Drive Most Business Solutions: 1. Data Retrieval & Filtering    • SELECT, WHERE, ORDER BY    → These handle your daily data-pulling needs    → Perfect for reports, dashboards, and fundamental analysis 2. Data Aggregation (The Real MVP)    • GROUP BY with COUNT/SUM/AVG    • HAVING for filtered aggregations    → Business metrics, KPIs, performance tracking    → Essential for management reporting 3. Data Relationships (The Game Changer)    • INNER JOIN - Finding matches    • LEFT JOIN - Keeping all records from one side    → Customer purchase history    → Product performance analysis    → User behavior tracking 4. Data Transformation Heroes    • CTEs (WITH clause) for step-by-step logic    • Window functions (ROW_NUMBER, LAG)    → Time-based analysis    → Ranking and comparative analysis    → MoM, YoY calculations made simple Why This 20% is Golden: - Solves 80% of business problems - Better performance than complex queries - Easier to maintain and debug - More readable for team collaboration - Works across all SQL databases Focus Point: Master these fundamentals deeply rather than scratching the surface of everything. It's not about knowing more commands but solving real problems efficiently. Combining these basics creatively can solve most "complex" business requirements.

If I were learning SQL in 2025, Here is exactly what I would do (+ resources) 👇 I have worked as a DS in 3 different companies. I have landed DS offers from 10 different companies. The number 1 skill I’ve used on the job & in interviews? It’s SQL. Yes, I’ve used SQL more than Python as a Data Scientist. So here's how to learn SQL from scratch. 𝟭. 𝗗𝗲𝘃𝗲𝗹𝗼𝗽 𝗮 𝘀𝘁𝗿𝗼𝗻𝗴 𝗳𝗼𝘂𝗻𝗱𝗮𝘁𝗶𝗼𝗻 𝗶𝗻 𝗿𝗲𝗹𝗮𝘁𝗶𝗼𝗻𝗮𝗹 𝗱𝗮𝘁𝗮𝗯𝗮𝘀𝗲𝘀 Boring…. can’t we jump start into learning SQL? No! SQL = storing + extracting data from relational DB. So it’s really helpful to know relational databases. K͟e͟y͟ ͟c͟o͟n͟c͟e͟p͟t͟s͟ ↳ Rows vs. columns ↳ Tables vs. schemas vs. database ↳ Keys (primary, foreign & unique) ↳ Indexes ↳ Table relationships ↳ Data types: numeric, string, datetime, boolean Learn relational databases here: https://lnkd.in/gyt3q8AC 𝟮. 𝗟𝗲𝗮𝗿𝗻 𝗯𝗮𝘀𝗶𝗰 𝗦𝗤𝗟 We'll start with getting data out of a SINGLE table. F͟o͟u͟n͟d͟a͟t͟i͟o͟n͟s͟ ↳ SELECT ↳ FROM ↳ WHERE ↳ ORDER BY ↳ LIMIT ↳ AS C͟l͟e͟a͟n͟i͟n͟g͟ ͟d͟a͟t͟a͟ ↳ DISTINCT ↳ LIKE ↳ BETWEEN ↳ COALESCE ↳ CASE WHEN B͟a͟s͟i͟c͟ ͟a͟n͟a͟l͟y͟t͟i͟c͟s͟ ↳ GROUP BY ↳ HAVING ↳ COUNT ↳ SUM ↳ AVG ↳ MIN / MAX How to do analyses with SQL: https://lnkd.in/gvZjepWf 𝟯. 𝗟𝗲𝘃𝗲𝗹 𝘂𝗽 𝘆𝗼𝘂𝗿 𝗦𝗤𝗟 𝘀𝗸𝗶𝗹𝗹𝘀 C͟o͟m͟b͟i͟n͟i͟n͟g͟ ͟t͟a͟b͟l͟e͟s͟ ↳ JOINs (INNER, LEFT, RIGHT, FULL) ↳ UNION and UNION ALL ↳ CTEs vs subqueries W͟i͟n͟d͟o͟w͟ ͟f͟u͟n͟c͟t͟i͟o͟n͟s͟ ↳ OVER ↳ PARTITION BY ↳ ORDER BY ↳ ROWS BETWEEN ↳ SUM, AVG, MIN, MAX with windows ↳ RANK, ROW_NUMBER, NTILE, LAG, LEAD Intermediate SQL: https://lnkd.in/gKM9WkyA Advanced SQL: https://lnkd.in/grhDPTdK 𝟰. 𝗟𝗲𝗮𝗿𝗻 𝗵𝗼𝘄 𝘁𝗼 𝗼𝗽𝘁𝗶𝗺𝗶𝘇𝗲 𝗦𝗤𝗟 𝗾𝘂𝗲𝗿𝗶𝗲𝘀 In the real-world we work with a lot of data at once. This is not a nice-to-have; it’s a must-have skill. Q͟u͟e͟r͟y͟ ͟o͟p͟t͟i͟m͟i͟z͟a͟t͟i͟o͟n͟ ͟t͟i͟p͟s͟ ↳ Avoid unnecessary data processing ↳ Reduce dataset size early ↳ Use indexes wisely ↳ Use EXPLAIN Get practice optimizing your queries: www.interviewmaster.ai 𝟱. 𝗔𝗽𝗽𝗹𝘆, 𝗯𝘂𝗶𝗹𝗱, 𝗮𝗻𝗱 𝗶𝘁𝗲𝗿𝗮𝘁𝗲 Build your own projects. But what projects should you build? Here are some ideas: ↳ Analyzing student’s mental health: https://lnkd.in/gZCUPpr5 ↳ What and where are the world’s oldest businesses: https://lnkd.in/gSWSdVt3 ↳ NYC public school test result scores: https://lnkd.in/g-SCsY5M 𝟲. 𝗣𝗿𝗲𝗽 𝗳𝗼𝗿 𝗿𝗲𝗮𝗹-𝘄𝗼𝗿𝗹𝗱 𝗗𝗮𝘁𝗮 𝗦𝗰𝗶𝗲𝗻𝗰𝗲 𝗿𝗼𝗹𝗲𝘀 Learn how SQL is used in the real-world: https://lnkd.in/gZt6bp-F And, of course, practice for SQL interviews - LeetCode: https://lnkd.in/gpcyVPh9 - Interview Master: https://lnkd.in/gvs2u8Bm - StrataScratch: https://lnkd.in/g9D9jZ9A ——— Starting from scratch? Learn all your SQL fundamentals in one place: https://lnkd.in/gNXW297S

The Only SQL MindMap You Need! No matter the data role—be it Data Analyst, Data Scientist, or Engineer—SQL is an absolute must-have skill! When I started learning SQL, I often found myself juggling between syntax, commands, and concepts. I know how overwhelming it can feel at the start. So, I thought—why not create a one-stop MindMap to simplify it all? Most of your daily SQL tasks revolve around mastering a few simple concepts that make everything else easier: ↳ Querying data efficiently ↳ Managing row-level operations ↳ Sorting data to make sense of trends ↳ Joining tables to combine information ↳ Grouping data to summarize key insights 𝐇𝐞𝐫𝐞’𝐬 𝐰𝐡𝐚𝐭 𝐲𝐨𝐮 𝐫𝐞𝐚𝐥𝐥𝐲 𝐧𝐞𝐞𝐝 𝐭𝐨 𝐟𝐨𝐜𝐮𝐬 𝐨𝐧: 1. 𝐃𝐚𝐭𝐚 𝐒𝐞𝐥𝐞𝐜𝐭𝐢𝐨𝐧 𝐌𝐚𝐬𝐭𝐞𝐫𝐲 ↳ SELECT is your primary tool for pulling data from tables. ↳ Leverage date functions to handle time-based data in reports. 2. 𝐉𝐨𝐢𝐧𝐬 ↳ LEFT JOIN is crucial when you need to keep all records from one table and match them with another. ↳ INNER JOIN helps you combine data from two tables, keeping only the matching rows. 3. 𝐅𝐢𝐥𝐭𝐞𝐫𝐢𝐧𝐠 𝐃𝐚𝐭𝐚 ↳ Master basic conditions with AND, OR. ↳ Use IN, NOT IN, and handle NULL values to refine your queries. 4. 𝐆𝐫𝐨𝐮𝐩𝐢𝐧𝐠 𝐃𝐚𝐭𝐚 ↳ GROUP BY helps organize data into meaningful categories. ↳ Use HAVING to filter your results after grouping. 5. 𝐑𝐨𝐰-𝐋𝐞𝐯𝐞𝐥 𝐎𝐩𝐞𝐫𝐚𝐭𝐢𝐨𝐧𝐬 & 𝐀𝐠𝐠𝐫𝐞𝐠𝐚𝐭𝐢𝐨𝐧𝐬 ↳ Use Window Functions like ROW_NUMBER(), RANK(), and DENSE_RANK() for advanced row-level analysis. ↳ Aggregations like SUM(), COUNT(), and AVG() are essential for summarizing data, and these also often go hand in hand with row-level operations. These functions help with operations such as ranking or calculating moving averages. Mastering these five categories will make your SQL tasks more efficient and effective. Focus on getting the basics right, and the rest will follow! Here’s a SQL mind map that you can use to visualize these core concepts and reinforce your learning. 𝐖𝐡𝐞𝐫𝐞 𝐭𝐨 𝐩𝐫𝐚𝐜𝐭𝐢𝐜𝐞? 1. Dataford - https://lnkd.in/enbEEgYd 2. Interview Query - https://lnkd.in/dzJET9aC 3. Analyst Builder - https://lnkd.in/dgVStuq8 4. LeetCode - https://leetcode.com/ 𝐏𝐫𝐨 𝐓𝐢𝐩: Practice consistently, tackle real-world problems, and challenge yourself! And remember: "𝐃𝐨𝐧’𝐭 𝐢𝐠𝐧𝐨𝐫𝐞 𝐒𝐐𝐋, 𝐨𝐫 𝐲𝐨𝐮 𝐦𝐢𝐠𝐡𝐭 𝐠𝐞𝐭 𝐢𝐠𝐧𝐨𝐫𝐞𝐝." 😉 ♻️ Save it for later or share it with someone who might find it helpful!