# 10 Silergy SQL Interview Questions (Updated 2024)

Updated on

March 2, 2024

At Silergy, SQL is used across the company for analyzing IoT device data for energy efficiency improvements and managing large databases for smart power product design optimizations. Because of this, Silergy almost always asks SQL query questions during interviews for Data Analytics, Data Science, and Data Engineering jobs.

So, to help you study for the Silergy SQL interview, here’s 10 Silergy SQL interview questions – how many can you solve?

## 10 Silergy SQL Interview Questions

### SQL Question 1: Identify Power Users in Silergy

You are a data analyst at Silergy. Silergy's success heavily depends on its power users, who are defined as the users who have made more than 50 purchases in a month. You are required to write a SQL query that can identify these power customers for the past three months.

For the purposes of this test you are given a transaction table, . Each row represents a purchase made by a user, with one user possibly making many purchases. The format of the table is as follows:

#### Answer:

This query will return users that made more than 50 purchases in any of the last three months. By truncating the transaction dates to the month level and grouping by these months and the user IDs, we can count the number of transactions per user per month. With the HAVING statement we get only the rows (i.e., the users and months) where this count exceeds 50.

To solve a related customer analytics question on DataLemur's free interactive coding environment, try this Microsoft SQL Interview problem:

### SQL Question 2: Analyze Monthly Average Product Ratings

Given a table that holds product reviews made by customers of Silergy, write a query to calculate the monthly average rating for each product.

The table has the following structure:

##### Example Input:
review_iduser_idsubmit_dateproduct_idstars
12012022-06-10 10:30:0010014
22022022-06-12 11:15:0010025
32032022-06-20 09:20:0010013
42042022-07-01 16:45:0010022
52052022-07-05 14:30:0010014

We are interested in creating an output table with one row for each product and month combination, showing the monthly average rating for each product.

##### Example Output:
monthproduct_idavg_rating
610013.50
610025.00
710014.00
710022.00

#### Answer:

An example SQL solution using PostgreSQL would look as follows:

This solution works by first extracting the month from the using PostgreSQL's function. This along with is grouped to form individual groups for calculation. The average star rating is then calculated for each product-month group using the function. Finally, the results are ordered by and for readability.

Pro Tip: Window functions are a frequent SQL interview topic, so practice all the window function problems on DataLemur

### SQL Question 3: Have you ever had to optimize a slow SQL query? How did you do it?

There's several steps you can take to troubleshoot a slow SQL query.

First things first, figure out why the query is slow! You can use and commands in PostgreSQL to identify any performance bottlenecks. After that, you can start changing your query, depending on what the source of the query performance issue is.

Generally, indexes can help speed up queries. Also de-normalizing your tables might help, to remove slow joins.

Lastly, you could always just upgrade your hardware! Time and money wasted improving query performance could just be better spent on mroe powerful database servers!

While this is a very surface-level approach to optimizing SQL query performance, it should do the trick for Data Analyst interviews and Data Science interviews at Silergy. Data Engineers should know a bit more about the and before the interview.

### SQL Question 4: Analysis of Product Sales and Inventory

At Silergy, a company that manufactures integrated power chips, your role includes monitoring the inventory and sales of different chip models. You are given access to two primary tables: and . The table holds data about the different models, with columns: , , , . The table has columns: , , , and .

Based on the current business needs, you are tasked with identifying the total sales (in units) and remaining stock for each model in the past month.

Provide a SQL query that can execute this task and include brief analysis of the output results.

##### Example Input:
ModelIdNameInStockUnitPrice
1ModelA5000\$20
2ModelB3000\$15
3ModelC4000\$25
4ModelD2000\$30
##### Example Input:
SaleIdModelIdDateOfSaleUnitsSold
112021-09-25200
212021-09-30100
322021-09-27300
432021-09-20400
542021-09-20500

#### Answer:

The SQL query in PostgreSQL would look something like this

Analysis: The resultant table will have three columns - 'model_name', 'total_sales' and 'remaining_stock'. The 'model_name' column will have the names of the chip models. 'total_sales' column will have total units sold in last month for each model and 'remaining_stock' column will have the remaining stock for each model. By analysing this table, you can understand the sales and inventory status of each chip model for the past month.

### SQL Question 5: What does do?

In SQL, the operator combines the result of two or more SELECT statements into a single result set. Note that each statement within the UNION must have the same number of columns and the columns must have similar data types. The operator removes duplicates from the final result set. If you want to include duplicates in the final result set, you can use the operator instead.

Here's an example of using the UNION operator to combine the results of two SELECT statements that retrieve data from tables of Silergy's Facebook ads and their Google ads:

This statement would return a combined result set of both Facebook and Google ads that have a spend greater than \$500.

### SQL Question 6: Calculate Click-Through-Rates for Silergy's Online Marketing Campaigns

Silergy Corp is interested in finding out the click-through rate (CTR) of their online marketing campaigns. Given two tables "impressions" and "clicks", calculate the CTR for each campaign.

For simplicity, assume that each impression and click can be uniquely associated with a campaign_id. The click-through rate is defined as the total number of clicks divided by the total number of impressions for each campaign, expressed as a percentage.

#### Sample Input:

impression_idcampaign_idimpression_date
1011706/08/2022 00:00:00
102506/08/2022 00:00:00
103406/08/2022 00:00:00
1041706/09/2022 00:00:00
105506/10/2022 00:00:00

#### Sample Input:

click_idcampaign_idclick_date
2011706/08/2022 00:01:00
202506/08/2022 00:01:00
203406/08/2022 00:01:00
2041706/09/2022 00:01:00
2051706/10/2022 00:01:00

#### Answer:

This SQL query calculates the click-through rate by joining the and table on the . The function is used to find the number of impressions and clicks for each campaign. It then calculates the CTR by dividing total clicks by total impressions and multiplying the result by 100 to get the percentage. The is used to perform the division between two integers as a floating point operation.

To solve another question about calculating rates, try this TikTok SQL Interview Question on DataLemur's interactive coding environment:

### SQL Question 7: What's the difference between and ?

The operator merges the output of two or more statements into a single result set. It ignores duplicated rows, and makes sure each row in the result set is unique.

For a concrete example, say you were a Data Analyst at Silergy working on a Marketing Analytics project. If you needed to get the combined result set of both Silergy's Google and Facebook ads you could execute this SQL query:

The operator works in a similar way to combine data from multiple statements, but it differs from the operator when it comes to handling duplicate rows. Whereas filters out duplicates (so if the same ad_name is run on both Facebook and Google, it only shows up once), outputs duplicate rows.

### SQL Question 8: Filtering Customer Records

As a database administrator at Silergy, you are tasked with the job of filtering customer data to target more effectively. The marketing team would like to create a new campaign for customers whose last names start with the letter "S". Write a SQL query to obtain a list of all customers with a last name starting with "S" from the "customers" table.

##### Example Input:
customer_idfirst_namelast_nameemailjoin_date
1258JohnDoejohn.doe@email.com01/15/2020
3624EmmaSmithemma.smith@email.com03/22/2021
7896SophieSuttonsophie.sutton@email.com06/12/2019
5412MichaelBrownmbrown@email.com07/05/2020
4317SarahSanderssanders.s@email.com11/25/2021

#### Answer:

This query uses the SQL LIKE operator to filter the records from the "customers" table. The '%' is a wildcard character that matches any number of characters. Therefore, 'S%' will match any string that starts with 'S'. The query will return all fields (*) for all records where the last name begins with 'S'. In this context, it will return the records for customers named Emma Smith, Sophie Sutton and Sarah Sanders.

### SQL Question 9: Analysing Customer and Product Data

As an analyst at Silergy, you are requested to write a SQL query to analyze the customer database and products database. The aim is to determine the total grouped purchases of each product by customer, including the customer's name and product's name.

Consider the following databases:

##### Example Input:
customer_idfirst_namelast_name
456JohnSmith
457SaraJohnson
458RyanWilliams
459OliviaBrown
460MichaelGarcia
##### Example Input:

|product_id|product_name| |:----:----| |523|TV| |524|Laptop| |525|Phone| |526|Tablet| |527|Speaker|

##### Example Input:
purchase_idcustomer_idproduct_id
9765456523
9766456524
9767457523
9768457525
9769458526
9770459527
9771460524
9772460526

#### Answer:

This query performs joins between the three tables based on in and , and in and . It then groups the resulting joint tables by first and last name from the table and product name from the table. The aggregate function is used to count the total purchases for each group.

Because join questions come up frequently during SQL interviews, practice this interactive Snapchat Join SQL question:

### SQL Question 10: How do foreign and primary keys differ?

To explain the difference between a primary key and foreign key, let's inspect employee data from Silergy's HR database:

:

+------------+------------+------------+------------+ | employee_id| first_name | last_name | manager_id | +------------+------------+------------+------------+ | 1 | Aubrey | Graham | 3 | | 2 | Marshal | Mathers | 3 | | 3 | Dwayne | Carter | 4 | | 4 | Shawn | Carter | | +------------+------------+------------+------------+

In this table, could be a primary key. It is unique for each row in the table and cannot contain null values.

could be a foreign key. It references the of the manager of each employee in the table, establishing a relationship between the employees and their managers. This foreign key allows you to easily query the table to find out who a specific employee's manager is, or to find out which employees report to a specific manager.

It is also possible for a table to have multiple foreign keys that reference different primary keys in other tables. For example, the table could have additional foreign keys for the of the department where each employee works, and the l of the location where each employee is based.

### Silergy SQL Interview Tips

The best way to prepare for a Silergy SQL interview is to practice, practice, practice. In addition to solving the above Silergy SQL interview questions, you should also solve the 200+ SQL coding questions which come from companies like FAANG tech companies and tech startups.

Each exercise has hints to guide you, full answers and best of all, there's an online SQL coding environment so you can right in the browser run your query and have it checked.

To prep for the Silergy SQL interview it is also helpful to solve interview questions from other tech companies like:

In case your SQL query skills are weak, forget about going right into solving questions – refresh your SQL knowledge with this SQL tutorial for Data Analytics.

This tutorial covers SQL concepts such as Union vs. UNION ALL and math functions in SQL – both of which show up frequently during Silergy interviews.

### Silergy Data Science Interview Tips

#### What Do Silergy Data Science Interviews Cover?

Besides SQL interview questions, the other types of problems covered in the Silergy Data Science Interview are:

#### How To Prepare for Silergy Data Science Interviews?

The best way to prepare for Silergy Data Science interviews is by reading Ace the Data Science Interview. The book's got:

• 201 Interview Questions from tech companies like Google & Microsoft
• A Refresher on Product Analytics, SQL & ML
• Great Reviews (900+ 5-star reviews on Amazon)