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SQL Interview Questions and answers Part 1 | SQL Scenario based Interview Question and Answer
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Aspiring data analysts and SQL developers preparing for technical interviews.
TL;DR
This video explains how to solve a common SQL interview question involving calculating the maximum transaction amount per customer and the ratio of each transaction to that maximum. It demonstrates two methods: using subqueries and common table expressions (CTEs).
Key Takeaways
- The problem requires calculating the maximum transaction amount per customer and the ratio of each transaction to this maximum.
- SQL queries can solve this by first identifying the maximum transaction amount for each customer.
- Subqueries are an effective method, where a subquery calculates the maximum amount per customer, then joined with the main table.
- Common Table Expressions (CTEs) offer an alternative, creating temporary named result sets for clarity and modularity.
- A CTE approach involves defining the base transaction data and then a separate CTE for the maximum transaction amount per customer.
- Both subqueries and CTEs allow for joining the aggregated maximum amounts back to individual transactions to compute the required ratio.
- The final output includes original transaction details, the maximum transaction amount for the customer, and the calculated ratio for each transaction.
In This Video
- 00:00SQL Interview Questions Part 1
Introduction to scenario-based SQL interview questions. Covers the first problem statement and its requirements.
- 00:22Transaction Table Structure
Details of the transaction table: customer ID, transaction ID, amount, and date.
- 01:07Calculating Maximum Transaction Amount
Objective is to find the maximum transaction amount per customer ID.
- 01:26Calculating Transaction Ratio
Requirement to calculate the ratio of each transaction amount to the maximum for that customer.
- 02:14Solving with Subquery
Explains how to use a subquery to find the maximum transaction amount and join it back.
- 04:21Solving with CTE
Demonstrates solving the problem using Common Table Expressions (CTEs).
- 05:51Conclusion and Next Steps
Summarizes the two techniques and encourages likes and subscriptions.
Questions & Answers
How to find max transaction amount per customer in SQL?
You can find the maximum transaction amount for each customer by using a subquery or a Common Table Expression (CTE). Group the transaction table by customer ID and select the MAX of the transaction amount.
How to calculate transaction amount ratio to max amount per customer in SQL?
After finding the maximum transaction amount per customer, join this result back to the original transaction table on customer ID. Then, calculate the ratio using the transaction amount and the maximum transaction amount.
What are the two methods to solve this SQL problem?
The problem can be solved using two methods: 1. Using a subquery. 2. Using a Common Table Expression (CTE).
Explain the subquery method for finding max transaction amount.
First, write a subquery to find the maximum transaction amount for each customer ID by grouping. Then, inner join the original transaction table with this subquery on customer ID.
Explain the CTE method for finding max transaction amount.
Create a CTE to store the main transaction table data. Then, create another CTE to find the maximum transaction amount per customer ID by grouping. Finally, join these two CTEs.
What columns are in the transaction table?
The transaction table has four columns: customer ID, transaction ID, transaction amount, and transaction date.
Key Terms
- SQL — SQL (Structured Query Language) is a standard language for managing and manipulating databases.
- Subquery — A subquery is a query nested inside another SQL query, often used to perform operations on the results of the outer query.
- CTE — A Common Table Expression (CTE) is a temporary, named result set that you can reference within a single SQL statement.