๐ SQL is the most important skill for Data Analysts. Almost every analytics job requires working with databases to extract, filter, analyze, and summarize data.
Understanding the following SQL concepts will help you write efficient queries and solve real business problems with data.
1๏ธโฃ SELECT Statement (Data Retrieval)
What it is: Retrieves data from a table.
SELECT name, salary
FROM employees;
Use cases: Retrieving specific columns, viewing datasets, extracting required information.
2๏ธโฃ WHERE Clause (Filtering Data)
What it is: Filters rows based on specific conditions.
SELECT *
FROM orders
WHERE order_amount > 500;
Common conditions: =, >, <, >=, <=, BETWEEN, IN, LIKE
3๏ธโฃ ORDER BY (Sorting Data)
What it is: Sorts query results in ascending or descending order.
SELECT name, salary
FROM employees
ORDER BY salary DESC;
Sorting options: ASC (default), DESC
4๏ธโฃ GROUP BY (Aggregation)
What it is: Groups rows with same values into summary rows.
SELECT department, COUNT(*)
FROM employees
GROUP BY department;
Use cases: Sales per region, customers per country, orders per product category.
5๏ธโฃ Aggregate Functions
What they do: Perform calculations on multiple rows.
SELECT AVG(salary)
FROM employees;
Common functions: COUNT(), SUM(), AVG(), MIN(), MAX()
6๏ธโฃ HAVING Clause
What it is: Filters grouped data after aggregation.
SELECT department, COUNT(*)
FROM employees
GROUP BY department
HAVING COUNT(*) > 5;
Key difference: WHERE filters rows before grouping, HAVING filters groups after aggregation.
7๏ธโฃ SQL JOINS (Combining Tables)
What they do: Combine tables.
-- INNER JOIN
SELECT orders.order_id, customers.customer_name
FROM orders
INNER JOIN customers
ON orders.customer_id = customers.customer_id;
-- LEFT JOIN
SELECT customers.customer_name, orders.order_id
FROM customers
LEFT JOIN orders
ON customers.customer_id = orders.customer_id;
Common types: INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL JOIN
8๏ธโฃ Subqueries
What it is: Query inside another query.
SELECT name
FROM employees
WHERE salary > (SELECT AVG(salary) FROM employees);
Use cases: Comparing values, filtering based on aggregated results.
9๏ธโฃ Common Table Expressions (CTE)
What it is: Temporary result set used inside a query.
WITH high_salary AS (
SELECT name, salary
FROM employees
WHERE salary > 70000
)
SELECT *
FROM high_salary;
Benefits: Cleaner queries, easier debugging, better readability.
๐ Window Functions
What they do: Perform calculations across rows related to current row.
SELECT name, salary, RANK() OVER (ORDER BY salary DESC) AS salary_rank
FROM employees;
Common functions: ROW_NUMBER(), RANK(), DENSE_RANK(), LAG(), LEAD()
Why SQL is Critical for Data Analysts
โข Extract data from databases
โข Analyze large datasets efficiently
โข Generate reports and dashboards
โข Support business decision-making
SQL Resources: https://whatsapp.com/channel/0029VanC5rODzgT6TiTGoa1v
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