SQL Server Subqueries are a critical aspect of SQL that enables developers and data analysts to write nested queries within their primary query. By allowing for the creation of complex queries, SQL Server Subqueries provide developers with more significant control and flexibility in their data analysis. These subqueries can be used to perform various operations, such as calculating the average salary of employees in a specific department, retrieving the second-highest salary in a company, or even joining multiple tables to retrieve specific data sets. This functionality can help data analysts to efficiently retrieve, organize and analyze large amounts of data from multiple sources. Ultimately, SQL Server Subqueries are an indispensable tool in the SQL language, providing developers and data analysts with the power and flexibility to handle complex data sets and perform precise, efficient data analysis.

Agenda

  1. Introduction to SQL Server Subqueries
  2. Different Concept Types with Industry Examples and Coding Examples
  3. Real-World Example Questions in the Healthcare Industry
  4. Most Commonly Asked Interview Question
  5. Conclusion

Introduction to SQL Server Subqueries

SQL Server Subqueries are a fundamental component of SQL. They allow you to write nested queries within your main query. They can be used to perform complex operations, such as finding the average salary of employees in a specific department or finding the second-highest salary in a company.

Different Concept Types with Industry Examples and Coding Examples:

Different Concept Types with Industry Examples and Coding Examples

Simple Subqueries

A simple subquery is a query within a query. It returns a single value, and it is used to solve a specific problem.

Example Question:
Find the department with the highest average salary in a healthcare company.

Coding Example:

SELECT
    department, AVG(salary)
FROM
    employees
GROUP BY
    department
HAVING
    AVG(salary) = (SELECT MAX(AVG(salary))
                   FROM employees
                   GROUP BY department)

Explanation:
In this example, the main query groups the employees by department and calculates the average salary for each department. The subquery inside the HAVING clause returns the maximum average salary. The main query then only returns departments with the highest average salary, which is the result of the subquery.

Correlated Subqueries

A correlated subquery is a subquery that depends on the values from the main query. It returns a set of values, and it is used to compare values between the main query and the subquery.

Example Question:
Find the names of employees who earn more than the average salary of their department in a healthcare company.

Coding Example:

SELECT
    name, salary, department
FROM
    employees e1
WHERE
    salary > (SELECT AVG(salary)
              FROM employees e2
              WHERE e1.department = e2.department)

Explanation:
In this example, the main query returns the name, salary, and department of all employees. The subquery inside the WHERE clause returns the average salary for each department. The main query then only returns the names and salaries of employees who earn more than the average salary of their department, which is the result of the subquery.

Multi-level Subqueries

A multi-level subquery is a subquery within a subquery. It is used to perform complex operations, such as finding the second-highest salary in a company.

Example Question:
Find the second-highest salary in a healthcare company.

Coding Example:

SELECT
    MAX(salary)
FROM
    employees
WHERE
    salary < (SELECT MAX(salary) FROM employees)

Explanation:
In this example, the subquery inside the WHERE clause returns the highest salary in the company. The main query then returns the second highest salary, which is the maximum salary that is less than the highest salary.

Real-World Example Questions in the Healthcare Industry

Script to generate tables and records:

-- Create Patients table
CREATE TABLE Patients (
  PatientID INT PRIMARY KEY,
  Name VARCHAR(50),
  VisitDate DATE
);

-- Insert records into Patients table
INSERT INTO Patients (PatientID, Name, VisitDate)
VALUES
(1, 'John Doe', '2022-01-01'),
(2, 'Jane Doe', '2022-01-15'),
(3, 'Jim Smith', '2022-02-01'),
(4, 'Jane Smith', '2022-02-15'),
(5, 'John Brown', '2022-03-01'),
(6, 'Jane Brown', '2022-03-15'),
(7, 'Jim Wilson', '2022-04-01'),
(8, 'Jane Wilson', '2022-04-15');

-- Create Treatments table
CREATE TABLE Treatments (
  TreatmentID INT PRIMARY KEY,
  PatientID INT,
  Cost MONEY,
  FOREIGN KEY (PatientID) REFERENCES Patients (PatientID)
);

-- Insert records into Treatments table
INSERT INTO Treatments (TreatmentID, PatientID, Cost)
VALUES
(1, 1, 100.00),
(2, 1, 200.00),
(3, 2, 150.00),
(4, 3, 125.00),
(5, 4, 175.00),
(6, 5, 225.00),
(7, 6, 200.00),
(8, 7, 175.00),
(9, 8, 150.00);

1. What is the total number of patients visited for each month in 2022, in the “Patients” table?

View Answer

2. What is the average cost of treatments for patients who visited the hospital in 2022, in the “Patients” and “Treatments” tables?

View Answer

3. How many patients have visited the hospital more than once in 2022, in the “Patients” table?

View Answer

Most Commonly Asked Interview Question and Answer in SQL Server

Q: What is a subquery in SQL Server and how have you used it in a previous project?

A: subquery in SQL Server is a query within another query. It returns a result set that can be used as input to the main query. I have used subqueries in a previous project to find the average cost of treatments for each patient, based on the total number of treatments they have received. To do this, I created a subquery to find the total cost of treatments for each patient and then used that result set as an input to the main query to find the average cost.

SELECT AVG(TotalCost) AS AverageCost
FROM (
  SELECT PatientID, SUM(Cost) AS TotalCost
  FROM Treatments
  GROUP BY PatientID
) AS Subquery

Conclusion

In this blog, we have discussed the different types of SQL Server subqueries and provided examples from the healthcare industry. We have also posted three real-world example questions, along with the script to generate the tables and records needed to answer them. Finally, we have answered the most commonly asked interview question about subqueries and provided a concrete example from a previous project.

Interested in a career in Data Analytics? Book a call with our admissions team or visit training.colaberry.com to learn more.

Book a Call

250 Replies to “SQL Server Subqueries in the Healthcare Industry”

  3. Thank you for your post. I really enjoyed reading it, especially because it addressed my issue. It helped me a lot and I hope it will also help others.

  25. Thanks for posting. I really enjoyed reading it, especially because it addressed my problem. It helped me a lot and I hope it will help others too.

  32. Thanks for posting. I really enjoyed reading it, especially because it addressed my problem. It helped me a lot and I hope it will help others too.

  34. I think this is among the most important information for me. And i’m glad reading your article. But should remark on some general things, The site style is great, the articles is really great : D. Good job, cheers

  35. This design is steller! You obviously know how to keep a reader amused. Between your wit and your videos, I was almost moved to start my own blog (well, almost…HaHa!) Fantastic job. I really enjoyed what you had to say, and more than that, how you presented it. Too cool!

  36. I cherished up to you will obtain performed right here. The sketch is attractive, your authored subject matter stylish. nonetheless, you command get bought an impatience over that you want be turning in the following. sick no doubt come further until now again since exactly the similar nearly very often inside case you defend this hike.

  37. you are really a good webmaster. The web site loading speed is amazing. It seems that you’re doing any unique trick. Furthermore, The contents are masterpiece. you’ve done a great job on this topic!

  38. hello!,I love your writing very much! share we be in contact more approximately your article on AOL? I need a specialist on this house to resolve my problem. Maybe that’s you! Taking a look ahead to peer you.

  39. Unquestionably believe that which you said. Your favourite justification seemed to be on the net the simplest thing to remember of. I say to you, I definitely get annoyed even as folks consider issues that they just do not know about. You controlled to hit the nail upon the top and outlined out the whole thing without having side-effects , other folks could take a signal. Will likely be again to get more. Thank you

  44. I do not even know how I ended up here, but I assumed this publish was once good. I don’t know who you might be however certainly you are going to a famous blogger when you are not already. Cheers!

  57. I needed to thank you for this excellent read!! I definitely loved every bit of it. I have you book-marked to check out new stuff you postÖ

  64. Hey There. I found your blog using msn. This is a reallywell written article. I’ll be sure to bookmark it andcome back to read more of your useful info. Thanks for the post.I will definitely return.

  66. Very well written article. It will be helpful to anybody who employess it, including me. Keep doing what you are doing – i will definitely read more posts.

  69. You could certainly see your enthusiasm in the paintings you write. The arena hopes for more passionate writers like you who aren at afraid to mention how they believe. All the time follow your heart.

  70. whoah this blog is great i really like reading your posts.Keep up the great work! You already know, lots of people arehunting round for this information, you can help them greatly.

  73. I’m not that much of a internet reader to be honest but your sites really nice, keep it up! I’ll go ahead and bookmark your website to come back in the future. Cheers

  74. Good web site! I truly love how it is simple on my eyes and the data are well written. I’m wondering how I might be notified whenever a new post has been made. I’ve subscribed to your RSS feed which must do the trick! Have a great day!

  76. I simply wished to thank you so much once again. I do not know the things I could possibly have used in the absence of these secrets contributed by you over that concern. Previously it was the distressing crisis in my view, but observing the expert mode you handled it made me to leap for delight. Now i am grateful for this work and as well , trust you realize what an amazing job you happen to be accomplishing training other individuals with the aid of your web site. Most likely you’ve never met all of us.

  77. What i don’t understood is if truth be told how you’re not actually much more well-preferred than you might be right now. You are very intelligent. You already know thus significantly relating to this subject, made me personally consider it from a lot of varied angles. Its like women and men don’t seem to be interested except it is one thing to accomplish with Girl gaga! Your personal stuffs outstanding. All the time handle it up!

  78. Hello, Neat post. There is a problem along with your site in web explorer, would test this… IE still is the market leader and a big section of other people will pass over your wonderful writing due to this problem.

  80. Superb blog you have here but I was curious about if you knew of any user discussion forums that cover the same topics talked about here? I’d really like to be a part of online community where I can get opinions from other knowledgeable individuals that share the same interest. If you have any suggestions, please let me know. Thanks a lot!

  81. Great beat ! I would like to apprentice while you amend your website, how could i subscribe for a weblog website? The account helped me a applicable deal. I had been tiny bit familiar of this your broadcast offered vivid transparent concept

  82. Do you have a spam issue on this site; I also am a blogger, and I was curious about your situation; many of us have developed some nice practices and we are looking to swap methods with others, why not shoot me an email if interested.

  83. Thanks for all of the effort on this web site. My mom delights in carrying out investigation and it’s really easy to understand why. Most people learn all concerning the compelling way you offer good things by means of this web blog and as well invigorate contribution from others on the subject matter while my child is studying a great deal. Enjoy the remaining portion of the new year. You’re the one carrying out a fantastic job.

  84. Hey There. I found your blog using msn. This is a really well written article. I’ll make sure to bookmark it and come back to read more of your useful info. Thanks for the post. I will certainly comeback.

  91. Aw, this was a very good post. Spending some time and actual effort to generate a top notch article… but what can I say… I procrastinate a whole lot and don’t manage to get anything done.

  113. I like whbat you guys are usually up too.This thpe of clever work and coverage! Keep upp the wonderrful worksguys I’ve added you guys to our blogroll.

  118. It’s really a great and useful piece of info. I’m glad that you shared this useful info with us. Please keep us up to date like this. Thanks for sharing.

  132. Everyone loves what you guys tend to be up too. This type ofclever work and coverage! Keep up the superb works guys I’ve incorporated youguys to my own blogroll.

  134. Awesome issues here. I am very satisfied to see your post. Thank you a lot and I am looking ahead to contact you. Will you please drop me a mail?

  136. Terrific post however , I was wondering if you could write a litte more on this subject?I’d be very grateful if you could elaborate a little bit further.Thank you!

  161. Thanks for another fantastic post. Where else may justanyone get that kind of information in such an ideal approach of writing?I’ve a presentation subsequent week, and I’m at the look for such info.

  165. hey there and thanks to your information ?I抳e definitely picked up anything new from proper here. I did then again expertise several technical issues the usage of this website, since I skilled to reload the website a lot of instances prior to I could get it to load correctly. I were wondering in case your hosting is OK? Not that I am complaining, however slow loading cases times will often have an effect on your placement in google and could damage your quality ranking if ads and ***********|advertising|advertising|advertising and *********** with Adwords. Anyway I抦 adding this RSS to my e-mail and can glance out for a lot extra of your respective intriguing content. Make sure you update this once more soon..

  170. Valuable information and excellent design you got here! I would like to thank you for sharing your thoughts and time into the stuff you post!! Thumbs up!

  180. Today’s companies do not read every one of the five hundred or higher resumes dumped on them – for a single job opening! In actual fact, they will gladly throw out 90 of them, if that resume does nothing to capture their interest.

  198. An interesting discussion is worth comment. I believe that you should write more on this topic, it might not be a taboo matter but typically people don’t discuss these issues. To the next! Many thanks!!

  213. I will immediately seize your rss feed as I can’t find your e-mail subscription hyperlink or e-newsletter service. Do you’ve any? Kindly let me understand so that I may subscribe. Thanks.

  217. Hi there! I’m at work browsing your blog from my newapple iphone! Just wanted to say I love reading your blog andlook forward to all your posts! Keep up the outstandingwork!

  222. Oh my goodness! Impressive atticle dude! Thank you, However I am having issues with your RSS.I don?t know the reason why I cannot join it. Is there anybody having identicalRSS issues? Anyone who knows the solution ccan you kindly respond?Thanx!!

Leave a Reply

Your email address will not be published. Required fields are marked *