Lessons learned rewriting a SQL query

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

Day 33/90 — SQL Series | Phase 2 Subquery in FROM = building a custom table mid-query. "Show only cities with more than 10 orders — sorted by order count." You cannot do this with WHERE alone because WHERE runs before GROUP BY. Solution: group first inside a subquery → then filter the grouped result. SELECT city, order_count FROM ( SELECT city, COUNT(*) AS order_count FROM orders GROUP BY city ) AS city_summary WHERE order_count > 10; The inner query creates a virtual table called city_summary. The outer query reads and filters it like a normal table. Rule: always give the inner query an alias — SQL requires it. CTEs do the exact same thing but cleaner — coming next week. #SQL #Subquery #DataAnalytics #LearnSQL #DataAnalyst

🛑 Stop dealing with negative numbers in your SQL reports! Need to find the difference between two values regardless of which one is higher? The ABS() function is your best friend. Whether you're calculating: ✅ Price discrepancies ✅ Absolute variance ✅ Distance metrics ... ABS() turns those negative numbers positive in a snap! ⚡  I just dropped a new video covering how to use it with practical examples: #SQL #DataAnalytics #DataScience #SQLTips #LearningSQL

🚀 EXISTS in SQL 💡 What is EXISTS? ✔️ Check if a subquery returns any rows ✔️ Returns TRUE if at least 1 row exists ✔️ Returns FALSE if no rows 🔍 How it works: ➡️ Outer query runs ➡️ Inner query checks for matching rows ➡️ If a match is found, the row is included ➡️ If no match, the row is excluded 🗝️ Key Concept 👉 EXISTS does not care about values 👉 It only checks if rows exist 🧠 Even if the subquery returns NULL ➡️ EXISTS can still be TRUE #SQL #DataAnalytics #LearningSQL #TechTips #InterviewPrep #DataEngineering

In x++, if you want to print the SQL statement of an AOT query, use this class internal final class RunMyQuery {   public static void main(Args _args)   {     Query query = new Query(queryStr(QueryName));     QueryRun queryRun;     str sql;     queryRun = new QueryRun(query);     sql = queryRun.query().getSQLStatement();     info(sql);   } }

🚀 JOIN vs Subquery – Which is Faster? Still confused between JOIN and Subquery in SQL? 👉 Here’s the simple logic: ✔ Subquery = Query inside query ✔ JOIN = Combine tables ✔ JOIN works faster for large data ⚡ ✔ Execution plan decides performance 💡 Learn smart, write optimized queries! 💬 Comment: JOIN or Subquery? 📌 Follow for more SQL tips

𝐒𝐐𝐋 𝐈𝐧𝐭𝐞𝐫𝐯𝐢𝐞𝐰 𝐂𝐡𝐚𝐥𝐥𝐞𝐧𝐠𝐞 | 𝐋𝐞𝐯𝐞𝐥: 𝐀𝐝𝐯𝐚𝐧𝐜𝐞𝐝 𝐂𝐡𝐚𝐥𝐥𝐞𝐧𝐠𝐞: Convert each row into multiple rows based on value Do it using pure SQL Avoid using loops (think set-based 💡) 𝐖𝐡𝐚𝐭 𝐭𝐡𝐢𝐬 𝐭𝐞𝐬𝐭𝐬: Recursive thinking Set-based SQL approach Understanding of row expansion Advanced SQL concepts (CTE / generate_series / window tricks) Drop your solution in the comments! P.S - Get create and insert statement in the first comment.

An interesting problem posted by Tyagi, which can be solved by using Recursive logic. Do check the comment to see my simple solution.

After a a few days off , I am here to prsent my Day 25 of SQL Night Study 🌙 Today I learned about the SQL EXISTS operator and it’s a very practical one. The EXISTS operator is used in a WHERE clause to check if a subquery returns any result. In simple terms: 👉 If the subquery finds at least one matching row, EXISTS returns TRUE 👉 If it finds nothing, it returns FALSE 🔹 Basic Syntax SELECT column_name FROM table_name WHERE EXISTS (subquery); 🔹 Example (Relatable) Imagine you have: A Customers table An Orders table You want to find customers who have placed at least one order. Query: SELECT customer_name FROM Customers c WHERE EXISTS ( SELECT 1 FROM Orders o WHERE o.customer_id = c.customer_id ); 👉 This will return only customers who have orders. 💡 Why this is useful Instead of counting or joining tables, EXISTS simply checks if a relationship exists, making it efficient and easy to read. Little by little, I am understanding how SQL helps answer real business questions. #SQL #SQLLearning #DataAnalytics #LearningInPublic #TechJourney #ContinuousLearning