12. Master Window Functions

Once your basics are strong, learn:

• ROW_NUMBER()

• RANK()

• DENSE_RANK()

• LAG()

• LEAD()

• SUM() OVER()

• AVG() OVER()

These are especially important for Data Analyst interviews.

13. Don't just memorize queries

Instead of memorizing: "This is the query to find the second-highest salary."

Understand the problem: "I need to rank salaries and identify the second position."

Then decide whether DENSE_RANK(), ROW_NUMBER(), a subquery, or another approach is appropriate.

14. Practice with business problems

Don't practice only: Find employees, Find salaries, Find departments

Practice realistic problems:

• Find customers who haven't purchased in 90 days

• Find the top 3 products in each category

• Calculate month-over-month sales growth

• Find duplicate transactions

• Identify customers whose spending increased

• Calculate employee retention

• Find the second-highest salary in each department

15. Learn to read execution plans later

Once you're comfortable with SQL, start learning:

• Indexes

• Query execution plans

• Table scans

• Index scans

• Query optimization

You don't need this on day one, but it's important as you progress.

🔥 Most important tip: Don't just watch SQL tutorials. Write SQL every day. Even 5–10 problems daily will build your confidence much faster than passive learning.

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