Question 1

What is SQL?

Accepted Answer

SQL (Structured Query Language) is used to store, retrieve, update, and analyze data from relational databases.

Question 2

Difference between WHERE and HAVING?

Accepted Answer

WHERE filters rows before aggregation. HAVING filters after aggregation.

Question 3

Difference between DELETE, TRUNCATE, and DROP?

Accepted Answer

DELETE: removes selected rows. TRUNCATE: removes all rows (faster). DROP: deletes the table itself.

Question 4

What is a primary key?

Accepted Answer

A column that uniquely identifies each row and cannot be NULL.

Question 5

What is a foreign key?

Accepted Answer

A column that references a primary key in another table to maintain relationships.

Question 6

Difference between INNER JOIN and LEFT JOIN?

Accepted Answer

INNER JOIN: only matching rows. LEFT JOIN: all left table rows + matched right rows.

Question 7

What is a RIGHT JOIN?

Accepted Answer

Returns all rows from the right table and matching rows from the left.

Question 8

What is a FULL OUTER JOIN?

Accepted Answer

Returns all rows from both tables, matched or unmatched.

Question 9

When would you use a SELF JOIN?

Accepted Answer

When a table needs to be joined with itself (e.g., employee-manager hierarchy).

Question 10

Difference between JOIN and UNION?

Accepted Answer

JOIN: combines columns. UNION: combines rows.

Question 11

What does GROUP BY do?

Accepted Answer

Groups rows to perform aggregate functions like COUNT, SUM, AVG.

Question 12

Can you use SELECT columns without GROUP BY?

Accepted Answer

No, unless the column is part of an aggregate function.

Question 13

Difference between COUNT(*) and COUNT(column)?

Accepted Answer

COUNT(*): counts all rows. COUNT(column): ignores NULL values.

Question 14

How to find duplicate records?

Accepted Answer

Use GROUP BY with HAVING COUNT(*) > 1.

Question 15

How to find the second highest salary?

Accepted Answer

Use ORDER BY with LIMIT or a subquery.

Question 16

What is a subquery?

Accepted Answer

A query inside another query, used for filtering or calculations.

Question 17

Difference between subquery and CTE?

Accepted Answer

Subquery: inline, less readable. CTE (WITH): reusable and cleaner.

Question 18

When should you use a CTE?

Accepted Answer

For complex logic, repeated queries, or readability.

Question 19

Can a subquery return multiple rows?

Accepted Answer

Yes, when used with IN, ANY, or EXISTS.

Question 20

What is EXISTS used for?

Accepted Answer

Checks if at least one row exists, faster than IN in large datasets.

SQL for Product Managers

BasicsWhat is SQL?

What is SQL?

BasicsDifference between WHERE and HAVING?

Difference between WHERE and HAVING?

BasicsDifference between DELETE, TRUNCATE, and DROP?

Difference between DELETE, TRUNCATE, and DROP?

BasicsWhat is a primary key?

What is a primary key?

BasicsWhat is a foreign key?

What is a foreign key?

JoinsDifference between INNER JOIN and LEFT JOIN?

Difference between INNER JOIN and LEFT JOIN?

JoinsWhat is a RIGHT JOIN?

What is a RIGHT JOIN?

JoinsWhat is a FULL OUTER JOIN?

What is a FULL OUTER JOIN?

JoinsWhen would you use a SELF JOIN?

When would you use a SELF JOIN?

JoinsDifference between JOIN and UNION?

Difference between JOIN and UNION?

AggregationsWhat does GROUP BY do?

What does GROUP BY do?

AggregationsCan you use SELECT columns without GROUP BY?

Can you use SELECT columns without GROUP BY?

AggregationsDifference between COUNT(*) and COUNT(column)?

Difference between COUNT(*) and COUNT(column)?

AggregationsHow to find duplicate records?

How to find duplicate records?

AggregationsHow to find the second highest salary?

How to find the second highest salary?

Subqueries & CTEsWhat is a subquery?

What is a subquery?

Subqueries & CTEsDifference between subquery and CTE?

Difference between subquery and CTE?

Subqueries & CTEsWhen should you use a CTE?

When should you use a CTE?

Subqueries & CTEsCan a subquery return multiple rows?

Can a subquery return multiple rows?

Subqueries & CTEsWhat is EXISTS used for?

What is EXISTS used for?

Window FunctionsWhat are window functions?

What are window functions?

Window FunctionsDifference between RANK() and DENSE_RANK()?

Difference between RANK() and DENSE_RANK()?

Window FunctionsWhat does ROW_NUMBER() do?

What does ROW_NUMBER() do?

Window FunctionsWhat is PARTITION BY?

What is PARTITION BY?

Window FunctionsUse case of window functions for PMs?

Use case of window functions for PMs?

PerformanceWhat is an index?

What is an index?

PerformanceWhen should you avoid indexes?

When should you avoid indexes?

PerformanceDifference between INNER JOIN and WHERE EXISTS?

Difference between INNER JOIN and WHERE EXISTS?

PerformanceHow do you handle NULL values?

How do you handle NULL values?

PerformanceOne SQL metric every PM should know?

One SQL metric every PM should know?

Practical BasicsCode ExampleWrite a query to find all unique job titles from the employees table.

Write a query to find all unique job titles from the employees table.

Practical BasicsCode ExampleSelect all details of customers who live in 'New York' or 'London'.

Select all details of customers who live in 'New York' or 'London'.

Practical BasicsCode ExampleFind all products that start with the letter 'A'.

Find all products that start with the letter 'A'.

Practical BasicsCode ExampleFind all orders where the shipping_date is missing (not yet shipped).

Find all orders where the shipping_date is missing (not yet shipped).

Practical BasicsCode ExampleCount the total number of orders placed in 2023.

Count the total number of orders placed in 2023.

Practical BasicsCode ExampleFind the total sales (revenue) for each product category.

Find the total sales (revenue) for each product category.

Practical BasicsCode ExampleFind categories that have a total revenue greater than $10,000.

Find categories that have a total revenue greater than $10,000.

Practical BasicsCode ExampleList the top 5 highest-paid employees.

List the top 5 highest-paid employees.

Practical BasicsCode ExampleCalculate the average order value (AOV) from the orders table.

Calculate the average order value (AOV) from the orders table.

Practical BasicsCode ExampleCreate a column called order_status that labels orders as 'High Value' if total > 500, else 'Standard'.