SQL Programming Resources
Find top SQL resources from global universities, cool projects, and learning materials for data analytics. Admin: @coderfun Useful links: heylink.me/DataAnalytics Promotions: @love_data
Show more📈 Analytical overview of Telegram channel SQL Programming Resources
Channel SQL Programming Resources (@sqlanalyst) in the English language segment is an active participant. Currently, the community unites 76 610 subscribers, ranking 1 633 in the Technologies & Applications category and 4 120 in the India region.
📊 Audience metrics and dynamics
Since its creation on невідомо, the project has demonstrated rapid growth, gathering an audience of 76 610 subscribers.
According to the latest data from 25 August, 2026, the channel demonstrates stable activity. Although there has been a change in the number of participants by 228 over the last 30 days and by 8 over the last 24 hours, overall reach remains high.
- Verification status: Not verified
- Engagement rate (ER): The average audience engagement rate is 2.19%. Within the first 24 hours after publication, content typically collects 1.04% reactions from the total number of subscribers.
- Post reach: On average, each post receives 1 678 views. Within the first day, a publication typically gains 796 views.
- Reactions and interaction: The audience actively supports content: the average number of reactions per post is 3.
- Thematic interests: Content is focused on key topics such as row, sql, customer_id, logic, desc.
📝 Description and content policy
The author describes the resource as a platform for expressing subjective opinions:
“Find top SQL resources from global universities, cool projects, and learning materials for data analytics.
Admin: @coderfun
Useful links: heylink.me/DataAnalytics
Promotions: @love_data”
Thanks to the high frequency of updates (latest data received on 26 August, 2026), the channel maintains relevance and a high level of publication reach. Analytics show that the audience actively interacts with content, making it an important point of influence in the Technologies & Applications category.
SELECT date, sales, SUM(sales) OVER (ORDER BY date) AS running_total FROM sales_data;
2. Conditional Aggregation with CASE WHEN:
Segment data within a single query, saving time and creating versatile summaries.
SELECT COUNT(CASE WHEN status = 'Completed' THEN 1 END) AS completed_orders FROM orders;
3. CTEs for Modular Queries:
Make complex queries more readable and reusable with CTEs.
WITH filtered_sales AS (SELECT * FROM sales_data WHERE region = 'North')
SELECT product, SUM(sales) FROM filtered_sales GROUP BY product;
4. Optimize with EXISTS vs. IN:
Use EXISTS for better performance in larger datasets.
SELECT * FROM customers c WHERE EXISTS (SELECT 1 FROM orders o WHERE o.customer_id = c.id);
5. Self Joins for Row Comparisons:
Compare rows within the same table, helpful for changes over time.
SELECT a.date, (a.sales - b.sales) AS sales_diff FROM sales_data a JOIN sales_data b ON a.date = b.date + INTERVAL '1' MONTH;
6. UNION vs. UNION ALL:
Combine results from multiple queries; UNION ALL is faster as it doesn’t remove duplicates.
7. Handle NULLs with COALESCE:
Replace NULLs with defaults to avoid calculation issues.
SELECT product, COALESCE(sales, 0) AS sales FROM product_sales;
8. Pivot Data with CASE Statements:
Transform rows into columns for clearer insights.
9. Extract Data with STRING Functions:
Useful for semi-structured data; extract domains, product codes, etc.
SELECT SUBSTRING(email, CHARINDEX('@', email) + 1, LEN(email)) AS domain FROM users;
10. Indexing for Faster Queries:
Indexes speed up data retrieval, especially on frequently queried columns.
Mastering these SQL tricks will optimize your queries, simplify logic, and enable complex analyses.
Here you can find SQL Interview Resources👇
https://t.me/DataSimplifier
Like this post if you need more 👍❤️
Share with credits: https://t.me/sqlspecialist
Hope it helps :)WITH sales_summary AS (
SELECT customer_id,
SUM(amount) AS total_sales
FROM sales
GROUP BY customer_id
)
SELECT *
FROM sales_summary
WHERE total_sales > 10000;
This makes your SQL easier to read and debug.
📌 16. Don't Memorize Interview Queries
Instead of memorizing:
"Query to find the second-highest salary"Understand the underlying concept:
Ranking → Ordering → Selecting the required rank.This allows you to solve variations of the same problem. 📌 17. Practice Real Business Scenarios ----- 2.12 ₽ · /balance_help
SELECT *
FROM employees
WHERE department = 'IT';
Think:
WHERE → Which rows do I need?
📌 3. Remember WHERE vs HAVING
This is one of the most common SQL interview questions.
WHERE → Filters rows before grouping
HAVING → Filters groups after aggregation
SELECT department, COUNT(*) AS employee_count
FROM employees
GROUP BY department
HAVING COUNT(*) > 10;
📌 4. Be Very Careful with JOINs
JOINs are extremely important for Data Analysts.
Before joining tables, understand:
• Primary key
• Foreign key
• One-to-one relationship
• One-to-many relationship
• Many-to-many relationship
A wrong JOIN can produce incorrect results and duplicate records.
📌 5. Understand INNER JOIN vs LEFT JOIN
Remember the basic idea:
INNER JOIN → Returns matching records from both tables.
LEFT JOIN → Returns all records from the left table and matching records from the right table.
This simple concept will help you solve many interview questions.
📌 6. Always Check for Duplicate Rows After a JOIN
If you expected 1,000 rows but your JOIN produces 10,000 rows, don't immediately use DISTINCT.
First investigate whether the JOIN relationship is causing multiple matches.
📌 7. Master GROUP BY
GROUP BY is essential for data analysis.
SELECT department, SUM(salary) AS total_salary
FROM employees
GROUP BY department;
Think:
GROUP BY → How do I want to summarize my data?
📌 8. Learn Aggregate Functions Properly
Master these functions:
• COUNT()
• SUM()
• AVG()
• MIN()
• MAX()
Practice them with GROUP BY and HAVING.
📌 9. Don't Forget NULL
NULL means missing or unknown value.
Incorrect:
WHERE salary = NULL
Correct:
WHERE salary IS NULL
Also learn:
• COALESCE()
• NULLIF()
📌 10. Learn CASE WHEN
CASE WHEN is extremely useful for creating business categories.
CASE
WHEN salary >= 100000 THEN 'High'
WHEN salary >= 50000 THEN 'Medium'
ELSE 'Low'
END
You'll use it frequently in real-world analytics.
📌 11. Don't Overuse DISTINCT
DISTINCT removes duplicate results.
But if you're using DISTINCT because your JOIN unexpectedly created duplicates, investigate the JOIN instead.
📌 12. Learn Date Functions
Data Analyst interviews frequently involve dates.
Practice questions involving:
• Year
• Month
• Quarter
• Date difference
• Month-over-month growth
• Year-over-year growth
• Rolling periods
Date-based SQL problems are extremely common in analytics.
📌 13. Start Learning Window Functions
Once you're comfortable with basic SQL, learn:
• ROW_NUMBER()
• RANK()
• DENSE_RANK()
• LAG()
• LEAD()
• SUM() OVER()
• AVG() OVER()
These are extremely important for Data Analyst interviews.
📌 14. Understand RANK vs DENSE_RANK
For example, if salaries are:
100000
100000
90000
80000
RANK() gives:
1
1
3
4
DENSE_RANK() gives:
1
1
2
3
This difference is frequently tested in interviews.
📌 15. Use CTEs for Complex Queries
Instead of writing one huge query, break the logic into smaller steps using a CTE.SELECT department, AVG(salary)
FROM employees
GROUP BY department;
5. Understand GROUP BY vs HAVING
• WHERE → filters rows before grouping
• HAVING → filters groups after aggregation
Example:
SELECT department, COUNT(*) AS employees
FROM employees
GROUP BY department
HAVING COUNT(*) > 10;
6. Master JOINs
For Data Analyst interviews, JOINs are extremely important. Learn:
• INNER JOIN
• LEFT JOIN
• RIGHT JOIN
• FULL OUTER JOIN
• CROSS JOIN
• SELF JOIN
Most importantly, understand why rows are included or excluded in each JOIN.
7. Always understand your keys
Know the difference between:
• Primary Key
• Foreign Key
• Composite Key
• Unique Key
Understanding relationships between tables will make JOINs much easier.
8. Don't ignore NULL
NULL does not mean:
• 0
• Empty string
• False
Learn how NULL behaves with: IS NULL, IS NOT NULL, COALESCE(), NULLIF()
9. Learn CASE WHEN early
CASE is one of the most useful SQL features for analytics.
SELECT employee,
salary,
CASE
WHEN salary >= 100000 THEN 'High'
WHEN salary >= 50000 THEN 'Medium'
ELSE 'Low'
END AS salary_category
FROM employees;
10. Practice subqueries
Understand queries inside queries:
SELECT *
FROM employees
WHERE salary > (
SELECT AVG(salary)
FROM employees
);
Then move toward correlated subqueries.
11. Learn CTEs
CTEs make complex SQL easier to read and maintain.
WITH sales_summary AS (
SELECT customer_id, SUM(amount) AS total_sales
FROM sales
GROUP BY customer_id
)
SELECT *
FROM sales_summary
WHERE total_sales > 10000;