SQL Interview Questions Summary

Introduction

• Speaker: Sahiti from Edureka
• Focus: Top 65 SQL interview questions
• Importance of SQL in modern data handling

Importance of SQL

• SQL is crucial for database management.
• Essential for aspiring Database Administrators.

Key SQL Concepts

1. Difference Between DELETE and TRUNCATE

• DELETE: Deletes specific rows, can roll back, data manipulation command.
• TRUNCATE: Deletes all rows, cannot roll back, data definition command, faster than DELETE.

2. Subsets of SQL

• Data Definition Language (DDL): Defines database schema.
• Data Manipulation Language (DML): Handles data manipulation.
• Data Control Language (DCL): Deals with permissions and controls.
• Transaction Control Language (TCL): Manages transaction operations.

3. Database Management Systems

• Definition: Software for capturing and analyzing data.
• Types:
  • Hierarchical
  • Relational
  • Network
  • Object-oriented

4. Table and Field

• Table: Collection of data in rows and columns.
• Field: Columns in a table.

5. Joins in SQL

• Combines rows from two or more tables based on related columns.
• Types:
  • Inner Join
  • Full Join
  • Left Join
  • Right Join

6. Data Types

• CHAR vs VARCHAR:
  • CHAR: Fixed-length strings.
  • VARCHAR: Variable-length strings.

7. Primary Key

• Uniquely identifies row in a table.
• Can be a single attribute or a combination of attributes.

8. Constraints

• Ensure data integrity within tables.
• Types:
  • NOT NULL
  • UNIQUE
  • CHECK
  • DEFAULT
  • INDEX

9. SQL vs MySQL

• SQL: Language for database management.
• MySQL: A relational database management system.

10. Unique Key and Foreign Key

• Unique Key: Identifies a single row, allows multiple null values.
• Foreign Key: Maintains referential integrity between tables.

11. Data Integrity

• Refers to accuracy and consistency of data stored in databases.

12. Indexes

• Used for quick data retrieval.
• Types:
  • Clustered Index: Alters data storage order.
  • Non-clustered Index: Creates a logical order.

13. SQL Queries

• Example to display current date: SELECT GETDATE();
• Example to find names starting with 'A': SELECT * FROM employees WHERE name LIKE 'A%';
• Counting records: SELECT COUNT(*) FROM table_name;

14. Normalization

• Process of organizing data to avoid redundancy.
• Types:
  • 1NF
  • 2NF
  • 3NF
  • BCNF.

15. ACID Properties

• Atomicity: Transactions are all or nothing.
• Consistency: Ensures data meets validation rules.
• Isolation: Controls concurrent transactions.
• Durability: Ensures committed transactions persist.

16. Triggers and Procedures

• Triggers: Automatic actions upon data modifications.
• Stored Procedures: Precompiled collections of SQL statements.

17. Operators in SQL

• Types include: Arithmetic, Comparison, Logical, etc.

18. SQL Functions

• Used for data manipulation, formatting, and conversions.

19. Views

• A virtual table combining data from one or more tables.

20. User Defined Functions

• Types: Scalar, Inline Table-Valued, Multi-statement functions.

Conclusion

• Acquired knowledge on SQL can significantly enhance job prospects.
• Contact Edureka for doubts or further learning opportunities.