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Equip yourself with the top 4 SQL concepts in 2022

  • Post published:September 23, 2022

Being a professional SQL expert is your new goal for today.

Are you aware of advanced SQL concepts? It is an abbreviation of Structured Query Language and is a necessary tool for the ones who work with data.

In the 21st century, everybody works with data, which demands many skilled data professionals. A SQL professional is not restricted to having the basic knowledge of advanced SQL concepts but also shows his skills in implementing it to work efficiently. 

It is what majorly recruiters explore SQL concepts for interviews when hiring an SQL expert.

Therefore, vteams has listed 4 top SQL concepts for an interview with queries, examples, and explanations following the trend running in 2022.

Here is the list of top SQL concepts; review your favorite part.

  1. ROW_NUMBERS () vs RANK () vs DENSE_RANK ()
  2. Extract required data from date & time sections
  3. Common Table Expressions (CTEs)
  4. CASE WHEN Statement

Okay, here we go!

ROW_NUMBERS () vs RANK () vs DENSE_RANK ()

Ranking records is a common concept for working with real data sets; the following are the scenarios used by different companies.

  1. Rank top product verticals through a different number of orders or generated revenue
  2. Get a movie name in each genre with the highest number of views
  3. Rank top selling brands within a certain number of units to be sold

A sequential integer involves ROW_NUMBER, RANK (), and DENSE_RANK () to record in a mentioned partition. Here is an example of a Dummy Sales Dataset to enlist different product categories and shipping addresses through descending order of a shipping cost.

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The code mentioned above represents the same syntax, but its output results in a different order.

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Table 1.1 Difference between ROW_NUMBERS () vs RANK () vs DENSE_RANK ()

RANK () retrieves ranked rows that rely on the ORDER BY clause.

The table above shows a tie between 1st two rows in the value of the Shipping Cost column.

RANK assigns a similar integer in both rows.

DENSE_RANK is the same as RANK but does not skip any number in the similarity index.

The blue highlighted box indicates the same thing.

Extract required data from date & time sections

In interviews, developers have to evaluate the monthly progress of data in the data set. If it is impossible, the developer must extract the required part of the date out of the date-time variable in the data. 

There are varieties of functions to extract different parts of data in a SQL environment. 

In general, a developer has to be aware of the following information.

Equip yourself with the top 4 SQL concepts in 2022 3

Here’s a demonstration of using the EXTRACT function to show the commonly extracted date parts and keywords.

Equip yourself with the top 4 SQL concepts in 2022 4

Common Table Expressions (CTEs)

In the present era, you need to query the outcome of another query, and the simplest way of doing this is to rely on sub-queries. Sometimes, they are difficult to read and debug due to increased complexity and computations.

To solve this problem, developers rely on CTEs to make things easier. CTEs tend to make things easier in writing and maintaining complex queries. 

For example, think about the following data extraction using sub-query

Equip yourself with the top 4 SQL concepts in 2022 5

This example of sub-queries involves more calculations within sub-queries and adding more sub-queries. It increases complexity by making the code more complex and less readable.

Here’s another example of a simplified version of the same subquery with CTE.

Equip yourself with the top 4 SQL concepts in 2022 6

The above code shows; that a complex subquery is now composed of simple blocks of codes to be used. 

CTEs create a transitory table from the outcome of a query to improve readability and maintenance.

An original data set comprised millions or billions of rows with 1000s of GB storage, and it involves calculating data from the tables.

This method is quite expensive and concludes that the best solution is to use CTEs.

CASE WHEN Statement

To run the query conditionally, you must rely on a CASE statement that implements if-else in SQL. CASE statement tests different conditions mentioned in the WHEN clause and returns the remaining value in the THEN clause.

In general terms, an unsatisfied condition will return the given value in the ELSE clause.

In real data projects, the CASE statements categorize the data based on different values in other columns. In other terms, it aggregates other functions.

Note: CASE_WHEN statement includes multiple WHEN…THEN clauses while skipping ELSE clauses as an option.

The most frequently used case of the CASE statement is Data Pivoting.

What is Data Pivoting?

It is a process through which you can rearrange the number of rows and columns in a certain way to review data from different perspectives.

Here is a situation, if you are dealing with an extended format in which the number of rows > a number of columns, get it in a wide format where a number of columns > a number of rows.

The CASE statement is user-friendly in similar situations. 

That’s all!

We hope you finished this article to learn advanced SQL concepts within no time and found it efficient to enhance your skills in SQL. 

Developers at vteams have usually relied on advanced SQL concepts for the past 3 years and found these concepts as interview questions for data analyst and data scientist positions.