🔹 1. What is SQL?
SQL (Structured Query Language) is used to store, retrieve, and manage data in relational databases.
🔹 2. What is a database?
A database is an organized collection of data stored electronically.
🔹 3. What is DBMS?
DBMS (Database Management System) is software used to manage databases (e.g., MySQL, Oracle).
🔹 4. What is RDBMS?
RDBMS stores data in tables with rows and columns and supports relationships between tables.
🔹 5. Difference between DBMS and RDBMS?
| DBMS | RDBMS |
|---|---|
| No relationships | Supports relationships |
| No constraints | Uses keys & constraints |
🔹 6. What is a table?
A table is a collection of related data in rows and columns.
🔹 7. What is a row?
A row represents a single record in a table.
🔹 8. What is a column?
A column represents a field or attribute in a table.
🔹 9. What is a primary key?
A primary key uniquely identifies each record in a table.
🔹 10. What is a foreign key?
A foreign key links one table to another.
🔹 11. What are SQL commands?
SQL commands are:
- DDL (CREATE, DROP, ALTER)
- DML (INSERT, UPDATE, DELETE)
- DQL (SELECT)
- TCL (COMMIT, ROLLBACK)
🔹 12. What is SELECT query?
Used to fetch data from a table.
SELECT * FROM students;🔹 13. What is WHERE clause?
Used to filter records.
SELECT * FROM students WHERE age > 18;🔹 14. What is INSERT statement?
Used to add data into table.
INSERT INTO students VALUES (1, 'Amit', 20);🔹 15. What is UPDATE statement?
Used to modify existing data.
UPDATE students SET age = 21 WHERE id = 1;🔹 16. What is DELETE statement?
Used to remove records.
DELETE FROM students WHERE id = 1;🔹 17. What is DROP?
Deletes entire table permanently.
🔹 18. What is TRUNCATE?
Removes all records but keeps table structure.
🔹 19. Difference between DELETE and TRUNCATE?
| DELETE | TRUNCATE |
|---|---|
| Removes selected rows | Removes all rows |
| Can use WHERE | Cannot use WHERE |
🔹 20. What is ORDER BY?
Used to sort data.
SELECT * FROM students ORDER BY age ASC;🔹 21. What is GROUP BY?
Groups rows with same values.
🔹 22. What is HAVING?
Used with GROUP BY for filtering groups.
🔹 23. What is JOIN?
Used to combine rows from multiple tables.
🔹 24. Types of JOIN?
- INNER JOIN
- LEFT JOIN
- RIGHT JOIN
- FULL JOIN
🔹 25. What is INNER JOIN?
Returns only matching records.
🔹 26. What is LEFT JOIN?
Returns all records from left table + matching from right.
🔹 27. What is RIGHT JOIN?
Returns all records from right table + matching from left.
🔹 28. What is FULL JOIN?
Returns all records from both tables.
🔹 29. What is alias in SQL?
Temporary name for table or column.
🔹 30. What is DISTINCT?
Removes duplicate records.
🔹 31. What is constraint?
Rules applied on table columns.
🔹 32. Types of constraints?
- NOT NULL
- UNIQUE
- PRIMARY KEY
- FOREIGN KEY
- CHECK
- DEFAULT
🔹 33. What is NULL?
Represents missing or unknown value.
🔹 34. What is indexing?
Improves search speed in database.
🔹 35. What is view?
A virtual table based on SQL query.
🔹 36. What is stored procedure?
A pre-written SQL code saved for reuse.
🔹 37. What is trigger?
Automatically executes when event occurs.
🔹 38. What is normalization?
Process of organizing data to reduce redundancy.
🔹 39. Types of normalization?
- 1NF
- 2NF
- 3NF
🔹 40. What is denormalization?
Adding redundancy to improve performance.
🔹 41. What is subquery?
A query inside another query.
🔹 42. What is alias for table?
Temporary name for table.
🔹 43. What is case statement?
Used for conditional logic in SQL.
🔹 44. What is UNION?
Combines results of two queries.
🔹 45. Difference between UNION and UNION ALL?
| UNION | UNION ALL |
|---|---|
| Removes duplicates | Keeps duplicates |
🔹 46. What is EXISTS?
Checks if subquery returns results.
🔹 47. What is IN operator?
Checks multiple values.
🔹 48. What is BETWEEN?
Used for range condition.
🔹 49. What is LIKE operator?
Used for pattern matching.
🔹 50. Why SQL is important?
SQL is used in:
- Web applications
- Banking systems
- E-commerce
- Data analysis