👉 SQL remains an absolute must-have skill for anyone working in Data Science or Analytics.
Virtually every organization manages its core information inside databases, and SQL is the key to extracting, transforming, and analyzing that data.
🔹 1. What is SQL?
SQL = Structured Query Language
👉 Used to:
✔️ Query data
✔️ Filter records
✔️ Perform calculations
✔️ Uncover business insights
🔥 2. Popular Database Engines
✔️ PostgreSQL
✔️ MySQL
✔️ Snowflake
✔️ Google BigQuery
🔹 3. Basic SQL Query
✅ The SELECT Clause
Used to fetch records from a table.
SELECT * FROM customers;
👉
* retrieves every single column. 🔹 4. Fetch Specific Columns
SELECT full_name, total_spent FROM customers;
🔹 5. WHERE Clause
Used to apply filters to your data.
SELECT * FROM customers WHERE age >= 25;
🔹 6. ORDER BY
Sort your results.
SELECT * FROM customers ORDER BY total_spent DESC;
✔️ ASC → Ascending (Lowest to Highest)
✔️ DESC → Descending (Highest to Lowest)
🔹 7. Aggregate Functions
Used for summary statistics.
Function: COUNT()
Purpose: Counts the number of rows
Function: SUM()
Purpose: Adds values together
Function: AVG()
Purpose: Finds the mean value
Function: MAX()
Purpose: Finds the highest value
Function: MIN()
Purpose: Finds the lowest value
✅ Example
SELECT AVG(total_spent) FROM customers;
🔹 8. GROUP BY
Used to categorize data into buckets.
SELECT country, SUM(total_spent) FROM customers GROUP BY country;
🔹 9. Why SQL is Critical?
✔️ #1 requested technical skill in job descriptions
✔️ Used daily by analysts, data engineers, & data scientists
✔️ Scales seamlessly with massive enterprise datasets