✅ 50 Must-Know SQL Concepts for Interviews 💾📊

📍 SQL Basics
1. What is SQL
2. Types of SQL commands (DDL, DML, DCL, TCL)
3. Database vs Table
4. Primary Key & Foreign Key
5. NULL vs NOT NULL

📍 Data Retrieval
6. SELECT statement
7. WHERE clause
8. DISTINCT keyword
9. ORDER BY clause
10. LIMIT / TOP

📍 Filtering & Conditions
11. LIKE, BETWEEN, IN
12. IS NULL & IS NOT NULL
13. AND, OR, NOT
14. CASE statements
15. Aliases using AS

📍 Joins (Very Important)
16. INNER JOIN
17. LEFT JOIN
18. RIGHT JOIN
19. FULL OUTER JOIN
20. SELF JOIN

📍 Aggregation & Grouping
21. COUNT(), SUM(), AVG()
22. MIN(), MAX()
23. GROUP BY clause
24. HAVING vs WHERE
25. GROUP BY with multiple columns

📍 Subqueries & Nested Queries
26. Scalar subqueries
27. Correlated subqueries
28. IN vs EXISTS
29. Using subqueries in SELECT
30. CTE (Common Table Expressions)

📍 Modifying Data
31. INSERT INTO
32. UPDATE
33. DELETE
34. UPSERT (MERGE)
35. TRUNCATE vs DELETE

📍 Constraints & Indexing
36. UNIQUE constraint
37. CHECK constraint
38. DEFAULT values
39. Indexes – clustered vs non-clustered
40. AUTO_INCREMENT / SERIAL

📍 Views & Stored Procedures
41. Creating and using Views
42. Stored Procedures basics
43. Functions vs Procedures
44. Triggers
45. Transactions (COMMIT, ROLLBACK)

📍 Optimization & Tools
46. EXPLAIN or Query Plan
47. Avoiding SELECT *
48. Normalization
49. Denormalization
50. Popular SQL platforms (MySQL, PostgreSQL, MS SQL Server)

SQL Resources: https://whatsapp.com/channel/0029VanC5rODzgT6TiTGoa1v

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