# 10 Ecolab SQL Interview Questions (Updated 2024)

Updated on

August 11, 2024

Data Analysts and Data Engineers at Ecolab write SQL queries to analyze water treatment data, including pH levels, chemical dosing rates, and flow rates. It is also used to optimize industrial cleaning procedures by identifying trends in equipment performance and maintenance schedules, the reason why Ecolab asks SQL questions during job interviews.

To help you practice for the Ecolab SQL interview, here’s 10 Ecolab SQL interview questions – scroll down to start solving them!

## 10 Ecolab SQL Interview Questions

### SQL Question 1: Calculate the Monthly Total and Average quantity of Chemicals Sold

Ecolab is a global leader in water, hygiene, and infection prevention solutions and services. Your role as a data analyst is to analyze the sales of chemicals Ecolab sold for each month. The 'sales' table maintains records of each chemical sold, its quantity and the date of sale.

You have to write a SQL query that calculates the total and average quantity of each chemical sold in each month. The resulting output should be sorted by month and then by total quantity in descending order.

##### Example Input:
sale_idsale_datechemical_idquantity_sold
1012022-01-15150
1022022-01-20260
1032022-01-25170
1042022-02-12140
1052022-02-15230
##### Example Output:
monthchemical_idtotal_quantityaverage_quantity
1112060
126060
214040
223030

In this query, we first extract the month from the column. Then, we group the data by and . The sum function calculates the total quantity sold for each medicine in each month. Then, the avg function calculates the average quantity sold. We have sorted the result by and then by in descending order to meet your requirement.

To solve a related window function SQL problem on DataLemur's free online SQL coding environment, solve this Amazon BI Engineer interview question:

### SQL Question 2: Second Highest Salary

Given a table of Ecolab employee salary data, write a SQL query to find the 2nd highest salary amongst all the employees.

#### Ecolab Example Input:

employee_idsalary
12500
2800
31000
41200

#### Example Output:

second_highest_salary
1200

Check your SQL query for this interview question and run your code right in DataLemur's online SQL environment:

You can find a detailed solution with hints here: 2nd Highest Salary.

### SQL Question 3: Name the different types of joins in SQL. What does each one do?

In SQL, a join is used to combine rows from different tables based on a shared key or set of keys, resulting in a single merged table of data.

There are four distinct types of JOINs: , , , and .

(INNER) JOIN: Retrieves records that have matching values in both tables involved in the join.

LEFT (OUTER) JOIN: Retrieves all the records/rows from the left and the matched records/rows from the right table.

RIGHT (OUTER) JOIN: Retrieves all the records/rows from the right and the matched records/rows from the left table.

FULL (OUTER) JOIN: Retrieves all the records where there is a match in either the left or right table.

### SQL Question 4: Finding the Average Amount of Water Saved per Project

Ecolab is a company dedicated to water, hygiene and energy technologies and services. In an effort to promote water conservation, the company undertakes several water-saving projects. Often, they might want to find out the average amount of water saved per project.

Given the below two tables, and , write a SQL query that returns the average amount of water saved per project.

##### Example Input:
project_idproject_namestart_dateend_date
1001Water Json01/01/202131/12/2021
1002Rain Check01/02/202128/02/2021
1003Aqua LLC01/03/202131/03/2021
1004Hidro Marvin01/04/202130/04/2021
1005Lagoon Eagle01/05/202131/05/2021
##### Example Input:
project_idsaving_datewater_saved
100101/03/2021100
100202/02/2021400
100224/02/2021300
100315/03/2021200
100410/04/2021500
100418/04/2021300
100509/05/2021400

In the above SQL query, we first join the table and table on , then we calculate the average amount of for each project, grouped by and . This will give us the average amount of water saved per project.

To practice a very similar question try this interactive Amazon Highest-Grossing Items Question which is similar for calculating highest values in categories or this Amazon Average Review Ratings Question which is similar for averaging calculations across groups.

### SQL Question 5: In SQL, what's the primary difference between the 'BETWEEN' and 'IN' operators?

The and operators are both used to filter data based on certain criteria, but they work in different ways. is used to select values within a range, while is used to select values that match a list.

For instance, if you have a table called that contains the salary of each employee, along with which country they reside in, you could use the operator to find all employees who make between $130k and$160k:

To find all employees that reside in France and Germany, you could use the operator:

### SQL Question 6: Find the Average Salvage Value of Equipment Per Division

Ecolab, as a global leader in water, hygiene, and infection prevention solutions and services, uses many pieces of equipment across various divisions. The salvage value represents the estimated worth of a piece of heavy equipment after its useful life.

In this question, we need to find the average salvage value of equipment for each division in Ecolab at the end of the year 2021.

##### Example Input:
equipment_iddivision_idpurchase_datesalvage_value
10012012018-11-291000
10022022019-10-101500
10032012020-09-011100
10042032019-08-241000
10052022019-06-151800
10062012021-04-201200
10072032021-05-25900

This code block outputs the average salvage value by division. The function calculates the average salvage value for each division identified by . The clause filters out equipment purchased after 2021. The clause groups the records by .

#### Example Output:

division_idavg_salvage_value
2011100
2021650
203950

This output table shows the average salvage value of the equipment per division till the end of year 2021.

### SQL Question 7: What is a database index, and what are the different types of indexes?

A database index is a way to optimize the performance of a database by reducing the amount of data that needs to be searched to retrieve a record.

There are several types of indexes that can be used in a database:

1. Primary index: a unique identifier is used to access the row directly.
2. Unique index: used to enforce the uniqueness of the indexed columns in a table.
3. Composite index: created on multiple columns of a table, is used to speed up the search process for multiple columns
4. Clustered index: determines the physical order of the data in a table

For a concrete example, say you had a table of Ecolab customer payments with the following columns: payment_id, customer_id, payment_amount, and payment_date.

Here's what a clustered index on the column would look like:

A clustered index on the column would determine the physical order of the records in the table based on the . This means that the records with the earliest values would be stored together physically in the table, followed by records with later payment_date values.

Having a clustered index on the column can speed up queries that filter or sort the data based on the payment_date, as the records are already physically sorted in the table. For example, if you want to retrieve all the payments made in the month of January, the database can use the clustered index to quickly locate and retrieve the desired records without having to search through the entire table.

### SQL Question 8: Find Customers Whose Names Match a Given Pattern

You are given a customers' table and need to find all customers whose first names begin with the letter 'A' and end in 'a' (e.g. "Amanda", "Anita", "Alicia" etc.). The customers' table has three columns: , and .

Write a SQL query to find all customers whose first names follow the above pattern and return their complete information from the table.

##### Example Input:
customer_idfirst_nameemail
C101Amandaamanda@example.com
C102Carloscarlos@example.com
C103Anitaanita@example.com
C104Johnjohn@example.com
C105Aliciaalicia@example.com
##### Example Output:
customer_idfirst_nameemail
C101Amandaamanda@example.com
C103Anitaanita@example.com
C105Aliciaalicia@example.com

This query selects all columns from the table where begins with 'A' and ends with 'a'. The percent symbol (%) in the LIKE clause is a wildcard character that matches any sequence of characters. Hence, 'A%A' matches any string that begins with 'A' and ends with 'a'.

### SQL Question 9: Calculate the Total Sales and Total Quantity of Each Product Category for Each Customer

Ecolab offers various products categorized into different categories to their customers. We have a table which contains detailed invoice data of each sale done by Ecolab, and a table which contains detailed data about each product. Your job is to write a SQL query that returns a list of every Ecolab customer with the total sales and total quantity of each product category they purchased from.

The table is structured as follows:

sale_idcustomer_idproduct_idquantitysale_price
100203002100
101203011150
102303005100
103403023200
104303011150

The table is structured as follows:

product_idcategory
300'Cleaning'
301'Kitchen'
302'Bathroom'

You may assume that in the table represents the price of each individual unit of product, and represents the quantity of units purchased in each sale.

This query calculates the total sales and total quantity per customer for each product category at Ecolab. It first establishes a connection between the sales and products tables using a JOIN operation on the common product_id field. Then, using a GROUP BY operation, it aggregrates rows with the same customer id and product category, and sums the quantity field and the product of sale price and quantity field for each group.

Since join questions come up routinely during SQL interviews, take a stab at this interactive Snapchat SQL Interview question using JOINS:

### SQL Question 10: What does do?

The function can take in multiple paramaters, and returns the first input paramater that is not null. If all arguments are null, the COALESCE function will return null too.

Suppose you have a table of Ecolab salespeople and the number of deals they closed. If a salesperson didn't close any deals, the data from the 3rd-party CRM system exports a NULL value.

sales_personclosed_deals
Jason WrightNULL
Drew Jackson3
Chris HoNULL
Samantha Perez4

To change these NULLs to zeros, you can use the function in the following way:

This would result in the following data:

sales_personclosed_deals
Jason Wright0
Drew Jackson3
Chris Ho0
Samantha Perez4

### How To Prepare for the Ecolab SQL Interview

The best way to prepare for a SQL interview, besides making sure you have strong SQL fundamentals, is to practice a ton of real SQL questions that were asked in recent job interviews. In addition to solving the earlier Ecolab SQL interview questions, you should also solve the 200+ SQL questions from real Data Science & Analytics interviews which come from companies like Microsoft, Google, and Meta.

Each DataLemur SQL question has multiple hints, step-by-step solutions and best of all, there's an online SQL coding environment so you can instantly run your SQL query and have it checked.

To prep for the Ecolab SQL interview it is also useful to practice interview questions from other chemical companies like:

Stay ahead of the curve with Ecolab's latest advancements in AI technology for the foodservice industry!

However, if your SQL coding skills are weak, don't worry about jumping right into solving questions – go learn SQL with this SQL tutorial for Data Analytics.

This tutorial covers things like handling timestamps and filtering strings based on patterns – both of which pop up frequently in SQL interviews at Ecolab.

### Ecolab Data Science Interview Tips

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

In addition to SQL interview questions, the other question categories to prepare for the Ecolab Data Science Interview are:

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

I think the best way to prep for Ecolab Data Science interviews is to read the book Ace the Data Science Interview.

It has 201 data interview questions sourced from Google, Microsoft & tech startups. The book's also got a crash course covering SQL, Product-Sense & ML. And finally it's helped a TON of people, which is why it's got over 1000+ 5-star reviews on Amazon.

While the book is more technical in nature, it's also crucial to prepare for the Ecolab behavioral interview. Start by understanding the company's values and mission.