Simplifying SQL JOINs: INNER, LEFT, RIGHT, and FULL OUTER JOIN

#Day-5 #SQL Series – 👉 Today I learned about primary key and foreign key in SQL. Understood how they help in uniquely identifying records and connecting tables. ⭐ primary key:- ✔️ primary key is type of constraint in a table that uniquely identifies each row(a unique id) ✔️ there is only 1primary key and it should be not null 👉Key points:- ⚡Must be unique (no duplicates) ⚡Cannot be NULL ⚡Only one primary key per table ⭐ foreign key:- ✔️ A Foreign Key is a column that links one table to another. 👉 Key points:- ⚡ It refers to a primary key in another table ⚡ Used to maintain relationships between tables ⚡ Can have duplicate values ⚡ Can be NULL (in most cases)  #SQL #Learning #MCA #Consistency

✅ Solved a SQL problem on StrataScratch — Day 51 of my SQL Journey 💪 After 50 days on LeetCode, I’ve started focusing more on real-world, business-driven SQL problems 📊 Today’s problem was about analysing how rankings change over time — not just activity, but improvement in position. I worked on: • Aggregating total comments per country by month • Ranking countries within each month using DENSE_RANK() • Comparing rankings between December and January • Identifying countries whose rank improved What I practised: • Window functions for ranking • Time-based aggregation using DATE functions • Comparing metrics across time periods • Turning raw activity into performance insights What stood out — Growth isn’t always about higher numbers. It’s about moving ahead. A country can increase activity… Yet still fall behind others. That’s why relative performance matters more than absolute values. SQL helps uncover not just change… but meaningful change. Consistent learning, one query at a time 🚀 #SQL #StrataScratch #DataAnalytics #LearningInPublic #SQLPractice

“Here is some basic SQL notes… saved for future me (and anyone else who needs it).” Because let’s be honest — we all learn SQL… and then forget the syntax the moment we actually need it 😅 So instead of pretending I’ll remember everything, I decided to document the basics: - Core queries - Filtering - Aggregations - Joins & more Nothing fancy. Just the stuff that actually gets used. Sometimes the smartest thing in tech isn’t knowing everything… it’s knowing where you saved it 😉 #SQL #DataAnalytics #DataScience #LearningInPublic #TechNotes

Day 26/90 — SQL Series | Week 4 "My WHERE clause is not filtering dates correctly." "My SUM is returning NULL instead of a number." 9 times out of 10 — it's a data type mismatch. CAST and CONVERT fix it. CAST('250' AS INT) → turns text into number so you can do math CAST('2024-01-15' AS DATE) → turns text into date so filters work CAST(order_id AS VARCHAR) → turns number into text for concatenation Rule: use CAST (works everywhere). Use CONVERT only when you need date formatting in SQL Server. #SQL #CastConvert #DataAnalytics #LearnSQL #DataAnalyst

We’ve officially entered the Intermediate SQL Series 🚀 Starting strong with JOINS — one of the most important SQL skills. Watch here 👇 https://lnkd.in/djRu4BbR

JOINs - when one table is not enough Every real database has more than one table. Users in one table. Orders in another. Departments here. Employees there. The data is split - because that's the right way to design it. No repetition, no mess. But when you need to ask a question that spans two tables, you need a JOIN. A JOIN connects two tables on a shared column - usually an ID. Think of it like a handshake between two tables. "Your user_id matches my user_id — let's combine." INNER JOIN returns only rows where there's a match in both tables. No match, no row. LEFT JOIN returns everything from the left table - and whatever matches from the right. If there's no match on the right side, you still get the left row, just with nulls. RIGHT JOIN is the opposite - everything from the right, matched or not. FULL JOIN gives you everything from both sides, matched or not. In real life, you'll use INNER JOIN and LEFT JOIN 95% of the time. Master those two first. #PostgreSQL #SQL #PostgreSQLIn30Days #100DaysOfCode #LearningInPublic #DataAnalytics

Most people learn SQL. Very few know how to use it properly. Because real SQL isn’t just SELECT. It’s structure, joins, aggregation and how you handle data. That’s where most mistakes happen. Swipe through → 💬 Comment “SQL” for practice resource.

The query that taught me the most about SQL performance: A query running 4 minutes on a 50M row table. The fix took 30 seconds. Here's what I learned: The query had a WHERE clause filtering on YEAR(transaction_date) = 2023. This function-wrapped column prevented partition pruning. The database scanned all 50M rows. Fix: WHERE transaction_date >= '2023-01-01' AND transaction_date < '2024-01-01' Result: 9 seconds. The partition pruning now skipped 11 of 12 monthly partitions. The lesson: any function applied to a filtered column in a WHERE clause breaks partition pruning and index usage. Common culprits: → DATE(), YEAR(), MONTH() on date columns → CAST() or CONVERT() on join columns → LOWER() or UPPER() on string filter columns Write predicates that let the engine use its optimization structures. #SQL #QueryOptimization #DataEngineering #Performance #Snowflake

SQL fundamentals feel complex… until you see the system behind it. Think like this: • Server → Database → Schema → Table → Like a city → building → floor → room • Row → One person’s record • Column → One type of detail (name, salary) • Primary Key → Aadhaar/unique ID Now SQL logic: • SELECT → What do you want? • FROM → Where from? • WHERE → Which ones? • GROUP BY → Combine similar • HAVING → Filter groups • ORDER BY → Sort results Real twist most beginners miss: You write SQL top → down But database runs it inside → out Lesson: SQL is not syntax. It’s structured thinking + logical flow. Once you understand the system → everything else becomes easy #SQL #DataEngineering #DataAnalytics #LearnSQL #CodingTips #TechLearning #Database #DataScience #DevCommunity

🚀 SQL Basics – Day 9: Stored Procedures (Super Simple) Today let’s learn how to save SQL logic and reuse it anytime 💡 👇 🔍 What is a Stored Procedure? 👉 A saved SQL code 👉 You can run it anytime 🧠 “Like a function in SQL” --- 📌 Create Procedure 💡 "CREATE PROCEDURE GetEmployees() BEGIN SELECT * FROM employees; END;" 👉 Save your query --- ▶️ Run Procedure 💡 "CALL GetEmployees();" 👉 Execute anytime --- ✏️ Procedure with Parameter 💡 "CREATE PROCEDURE GetByDept(IN dept_name VARCHAR(50)) BEGIN SELECT * FROM employees WHERE department = dept_name; END;" 👉 Pass value while running --- 😄 Easy way to remember: Procedure = Saved code CREATE = Save CALL = Run Parameter = Input value --- ✨ Conclusion: Stored procedures save time and reduce repeated work 💪 They make your SQL more powerful and reusable 🚀 📌 Work smart by writing once and using many times! #SQL #DataAnalytics #SQLBasics #StoredProcedure #LearningSQL #Day9 #DataAnalyst