SQL Interview Questions with Answers 👇👇
https://www.linkedin.com/posts/sql-analysts_sql-interview-sqlinterview-activity-7178076668752760832-C2Fy?utm_source=share&utm_medium=member_android

Many people pay too much to learn SQL, but my mission is to break down barriers. I have shared complete learning series to learn SQL from scratch.

Here are the links to the SQL series

Complete SQL Topics for Data Analyst: https://t.me/sqlspecialist/523

Part-1: https://t.me/sqlspecialist/524

Part-2: https://t.me/sqlspecialist/525

Part-3: https://t.me/sqlspecialist/526

Part-4: https://t.me/sqlspecialist/527

Part-5: https://t.me/sqlspecialist/529

Part-6: https://t.me/sqlspecialist/534

Part-7: https://t.me/sqlspecialist/534

Part-8: https://t.me/sqlspecialist/536

Part-9: https://t.me/sqlspecialist/537

Part-10: https://t.me/sqlspecialist/539

Part-11: https://t.me/sqlspecialist/540

Part-12:
https://t.me/sqlspecialist/541

Part-13: https://t.me/sqlspecialist/542

Part-14: https://t.me/sqlspecialist/544

Part-15: https://t.me/sqlspecialist/545

Part-16: https://t.me/sqlspecialist/546

Part-17: https://t.me/sqlspecialist/549

Part-18: https://t.me/sqlspecialist/552

Part-19: https://t.me/sqlspecialist/555

Part-20: https://t.me/sqlspecialist/556

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Complete Python Topics for Data Analysts: https://t.me/sqlspecialist/548

Complete Excel Topics for Data Analysts: https://t.me/sqlspecialist/547

I'll continue with learning series on Python, Power BI, Excel & Tableau.

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50 SQL Project Ideas
👇👇
https://www.instagram.com/reel/C5RT8E6Npbc/?igsh=M2NyN3Uzd2o2YzUx

I am planning to start a SQL Interview Preparation Series with 25+ practical questions. Like if interested 😄

Few ways to optimise SQL Queries 👇👇

Use Indexing: Properly indexing your database tables can significantly speed up query performance by allowing the database to quickly locate the rows needed for a query.

Optimize Joins: Minimize the number of joins and use appropriate join types (e.g., INNER JOIN, LEFT JOIN) to ensure efficient data retrieval.

Avoid SELECT * : Instead of selecting all columns using SELECT *, explicitly specify only the columns needed for the query to reduce unnecessary data transfer and processing overhead.

Use WHERE Clause Wisely: Filter rows early in the query using WHERE clause to reduce the dataset size before joining or aggregating data.

Avoid Subqueries: Whenever possible, rewrite subqueries as JOINs or use Common Table Expressions (CTEs) for better performance.

Limit the Use of DISTINCT: Minimize the use of DISTINCT as it requires sorting and duplicate removal, which can be resource-intensive for large datasets.

Optimize GROUP BY and ORDER BY: Use GROUP BY and ORDER BY clauses judiciously, and ensure that they are using indexed columns whenever possible to avoid unnecessary sorting.

Consider Partitioning: Partition large tables to distribute data across multiple nodes, which can improve query performance by reducing I/O operations.

Monitor Query Performance: Regularly monitor query performance using tools like query execution plans, database profiler, and performance monitoring tools to identify and address bottlenecks.

Hope it helps :)

Here are some essential SQL tips for beginners 👇👇

◆ Primary Key = Unique Key + Not Null constraint
◆ To perform case insensitive search use UPPER() function ex. UPPER(customer_name) LIKE ‘A%A’
◆ LIKE operator is for string data type
◆ COUNT(*), COUNT(1), COUNT(0) all are same
◆ All aggregate functions ignore the NULL values
◆ Aggregate functions MIN, MAX, SUM, AVG, COUNT are for int data type whereas STRING_AGG is for string data type
◆ For row level filtration use WHERE and aggregate level filtration use HAVING
◆ UNION ALL will include duplicates where as UNION excludes duplicates 
◆ If the results will not have any duplicates, use UNION ALL instead of UNION
◆ We have to alias the subquery if we are using the columns in the outer select query
◆ Subqueries can be used as output with NOT IN condition.
◆ CTEs look better than subqueries. Performance wise both are same.
◆ When joining two tables , if one table has only one value then we can use 1=1 as a condition to join the tables. This will be considered as CROSS JOIN.
◆ Window functions work at ROW level.
◆ The difference between RANK() and DENSE_RANK() is that RANK() skips the rank if the values are the same.
◆ EXISTS works on true/false conditions. If the query returns at least one value, the condition is TRUE. All the records corresponding to the conditions are returned.

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Top 10 Websites to Practice SQL Skills 👇👇
https://www.instagram.com/reel/C5csFy9N5v6/?igsh=eGEwbjRnMWwyejNo

SQL CHEAT SHEET👩‍💻

Here is a quick cheat sheet of some of the most essential SQL commands:

SELECT - Retrieves data from a database

UPDATE - Updates existing data in a database

DELETE - Removes data from a database

INSERT - Adds data to a database

CREATE - Creates an object such as a database or table

ALTER - Modifies an existing object in a database

DROP -Deletes an entire table or database

ORDER BY - Sorts the selected data in an ascending or descending order

WHERE – Condition used to filter a specific set of records from the database

GROUP BY - Groups a set of data by a common parameter

HAVING - Allows the use of aggregate functions within the query

JOIN - Joins two or more tables together to retrieve data

INDEX - Creates an index on a table, to speed up search times.

Top 5 SQL Projects for freshers https://www.linkedin.com/posts/sql-analysts_many-freshers-face-the-challenge-of-finding-activity-7185123403492646912-Dqkj?utm_source=share&utm_medium=member_android

30 commonly asked questions in database management system (DBMS) interviews
👇👇

1. What is a DBMS?
2. Differentiate between DBMS and RDBMS.
3. What are the advantages and disadvantages of using a DBMS?
4. Explain the three levels of data abstraction in DBMS.
5. What is a database schema?
6. Define normalization and its importance in database design.
7. What are the different types of database models?
8. What is ACID (Atomicity, Consistency, Isolation, Durability) in DBMS?
9. What is a primary key, and why is it important?
10. Explain the concept of foreign keys.
11. Differentiate between a candidate key, primary key, and super key.
12. What is a transaction in a database?
13. Describe the differences between DELETE, TRUNCATE, and DROP commands.
14. What is a view in a database?
15. Explain indexing in databases.
16. What is a stored procedure?
17. What are the advantages of using stored procedures?
18. Describe the differences between clustered and non-clustered indexes.
19. What is a deadlock in DBMS?
20. How can you avoid deadlocks in a database?
21. What is data redundancy, and how can it be minimized?
22. What is a trigger in a database?
23. Describe the different types of joins in SQL.
24. What is a constraint in a database?
25. Explain the differences between a unique key and a primary key.
26. How does SQL differ from NoSQL databases?
27. What is the CAP theorem, and how does it relate to databases?
28. Explain the concept of data warehousing.
29. What are OLTP and OLAP, and how do they differ?
30. How would you approach database performance tuning and optimization?

Database keys

Database keys are essential for organizing and managing data effectively. In this post, we'll explore ten key concepts that every IT professional should know.

1. 🗝 𝗣𝗿𝗶𝗺𝗮𝗿𝘆 𝗞𝗲𝘆
- A unique identifier for each record in a table.
- Cannot be null.
- Ensures that each row is unique.

2. 🌉 𝗙𝗼𝗿𝗲𝗶𝗴𝗻 𝗞𝗲𝘆
- A field in one table that refers to the Primary Key of another table.
- Establishes relationships between tables.

3. 🧩 𝗖𝗼𝗺𝗽𝗼𝘀𝗶𝘁𝗲 𝗞𝗲𝘆
- A combination of two or more columns that uniquely identifies each record.
- Useful when a single column can't uniquely identify a record.

4. 💪 𝗦𝘂𝗽𝗲𝗿 𝗞𝗲𝘆
- One or more columns that can uniquely identify a record.
- A Primary Key is a type of Super Key.

5. 🏅 𝗖𝗮𝗻𝗱𝗶𝗱𝗮𝘁𝗲 𝗞𝗲𝘆
- A column or set of columns that could be the Primary Key.
- Must be unique.

6. 🔍 𝗨𝗻𝗶𝗾𝘂𝗲 𝗞𝗲𝘆
- Ensures uniqueness for a column or column combination.
- Similar to Primary Key but allows one null value.

7. 🛤 𝗔𝗹𝘁𝗲𝗿𝗻𝗮𝘁𝗲 𝗞𝗲𝘆
- A Candidate Key that isn't the Primary Key.
- Another option for a unique identifier.

8. 🍃 𝗡𝗮𝘁𝘂𝗿𝗮𝗹 𝗞𝗲𝘆
- A key that's a natural part of the data, like an email address.

9. 🎭 𝗦𝘂𝗿𝗿𝗼𝗴𝗮𝘁𝗲 𝗞𝗲𝘆
- An artificial key created when no natural unique identifier exists.

10. 🔑 𝗦𝗲𝗰𝗼𝗻𝗱𝗮𝗿𝘆 𝗞𝗲𝘆
- Used for data retrieval, not identification.
- Helps create non-clustered indexes.

Top 20 SQL Interview Questions
👇👇
https://www.linkedin.com/posts/sql-analysts_here-is-the-list-of-top-20-sql-interview-activity-7188152088822988800-nuUU?utm_source=share&utm_medium=member_android

SQL Roadmap 👇👇
https://www.linkedin.com/posts/sql-analysts_complete-roadmap-to-learn-sql-step-activity-7189269440318869504-rKoq?utm_source=share&utm_medium=member_android

Basics of SQL 👇👇

1. SQL (Structured Query Language) is a standard programming language used for managing and manipulating relational databases.

2. SQL operates through simple, declarative statements. These statements are used to perform tasks such as querying data, updating data, inserting data, and deleting data from a database.

3. The basic SQL commands include SELECT, INSERT, UPDATE, DELETE, CREATE, and DROP.

4. The SELECT statement is used to retrieve data from a database. It allows you to specify the columns you want to retrieve and filter the results using conditions.

5. The INSERT statement is used to add new records to a table in a database.

6. The UPDATE statement is used to modify existing records in a table.

7. The DELETE statement is used to remove records from a table.

8. The CREATE statement is used to create new tables, indexes, or views in a database.

9. The DROP statement is used to remove tables, indexes, or views from a database.

10. SQL also supports various operators such as AND, OR, NOT, LIKE, IN, BETWEEN, and ORDER BY for filtering and sorting data.

11. SQL also allows for the use of functions and aggregate functions like SUM, AVG, COUNT, MIN, and MAX to perform calculations on data.

12. SQL statements are case-insensitive but conventionally written in uppercase for readability.

13. SQL databases are relational databases that store data in tables with rows and columns. Tables can be related to each other through primary and foreign keys.

14. SQL databases use transactions to ensure data integrity and consistency. Transactions can be committed (saved) or rolled back (undone) based on the success of the operations.

15. SQL databases support indexing for faster data retrieval and performance optimization.

16. SQL databases can be queried using tools like MySQL, PostgreSQL, Oracle Database, SQL Server, SQLite, and others.

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Hope it helps :)

Introduction to Databases with SQL: Free Harvard Course
👇👇
https://cs50.harvard.edu/sql/2023/

If you are trying to transition into the data analytics domain and getting started with SQL, focus on the most useful concept that will help you solve the majority of the problems, and then try to learn the rest of the topics:

👉🏻 Basic Aggregation function:
1️⃣ AVG
2️⃣ COUNT
3️⃣ SUM
4️⃣ MIN
5️⃣ MAX

👉🏻 JOINS
1️⃣ Left
2️⃣ Inner
3️⃣ Self (Important, Practice questions on self join)

👉🏻 Windows Function (Important)
1️⃣ Learn how partitioning works
2️⃣ Learn the different use cases where Ranking/Numbering Functions are used? ( ROW_NUMBER,RANK, DENSE_RANK, NTILE)
3️⃣ Use Cases of LEAD & LAG functions
4️⃣ Use cases of Aggregate window functions

👉🏻 GROUP BY
👉🏻 WHERE vs HAVING
👉🏻 CASE STATEMENT
👉🏻 UNION vs Union ALL
👉🏻 LOGICAL OPERATORS

Other Commonly used functions:
👉🏻 IFNULL
👉🏻 COALESCE
👉🏻 ROUND
👉🏻 Working with Date Functions
1️⃣ EXTRACTING YEAR/MONTH/WEEK/DAY
2️⃣ Calculating date differences

👉🏻CTE
👉🏻Views & Triggers (optional)

Here is an amazing resources to learn & practice SQL: https://bit.ly/3FxxKPz

Share with credits: https://t.me/sqlspecialist

Hope it helps :)

SQL Mindmap 👇👇
https://www.linkedin.com/posts/sql-analysts_many-people-pay-too-much-to-learn-sql-but-activity-7190349055363846144-pXnP?utm_source=share&utm_medium=member_android

SQL Quick Notes
👇👇
https://www.linkedin.com/posts/sql-analysts_sql-quick-notes-activity-7196358639568220160-Azh2?utm_source=share&utm_medium=member_android