Top 10 Interview Questions You Must Know

 

1. Find Duplicate Records

SELECT Name,
       COUNT(*)
FROM Employee
GROUP BY Name
HAVING COUNT(*) > 1;

---

2. Delete Duplicate Records

WITH CTE AS
(
SELECT *,
ROW_NUMBER() OVER
(
PARTITION BY Name
ORDER BY ID
) rn
FROM Employee
)
DELETE FROM CTE
WHERE rn > 1;

---

3. Find 2nd Highest Salary

SELECT Salary
FROM
(
SELECT Salary,
DENSE_RANK() OVER
(ORDER BY Salary DESC) rk
FROM Employee
)x
WHERE rk=2;

---

4. Find 3rd Highest Salary

Change rk=2 to:

WHERE rk=3

---

5. Latest Order Per Customer

SELECT *
FROM
(
SELECT *,
ROW_NUMBER() OVER
(
PARTITION BY CustomerID
ORDER BY OrderDate DESC
) rn
FROM Orders
)x
WHERE rn=1;

---

6. Employees Earning Above Department Average

SELECT *
FROM Employee e
WHERE Salary >
(
SELECT AVG(Salary)
FROM Employee
WHERE DeptID=e.DeptID
);

---

7. Customers With No Orders

SELECT c.*
FROM Customers c
LEFT JOIN Orders o
ON c.CustomerID=o.CustomerID
WHERE o.CustomerID IS NULL;

---

8. Running Total

SUM(Sales) OVER(ORDER BY Date)

---

9. Month-over-Month Growth

LAG(Sales) OVER(ORDER BY Month)

---

10. Top 3 Salaries Per Department

DENSE_RANK()
OVER(PARTITION BY DeptID
ORDER BY Salary DESC)

For a Tableau/BI Architect interview, these 10 patterns alone cover roughly 70–80% of SQL coding questions asked in analytics, reporting, data warehousing, and BI projects.