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12 essential SQL concepts for data scientists: Tips and examples

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Ayesha Saleem

April 24

SQL (Structured Query Language) is an important tool for data scientists. It is a programming language used to manipulate data stored in relational databases. Mastering SQL concepts allows a data scientist to quickly analyze large amounts of data and make decisions based on their findings. Here are some essential SQL concepts that every data scientist should know:

First, understanding the syntax of SQL statements is essential in order to retrieve, modify or delete information from databases. For example, statements like SELECT and WHERE can be used to identify specific columns and rows within the database that need attention. A good knowledge of these commands can help a data scientist perform complex operations with ease.

Second, developing an understanding of database relationships such as one-to-one or many-to-many is also important for a data scientist working with SQL.

Here’s an interesting read about Top 10 SQL commands

Let’s dive into some of the key SQL concepts that are important to learn for a data scientist.  

1. Formatting Strings

We are all aware that cleaning up the raw data is necessary to improve productivity overall and produce high-quality decisions. In this case, string formatting is crucial and entails editing the strings to remove superfluous information. For transforming and manipulating strings, SQL provides a large variety of string methods. When combining two or more strings, CONCAT is utilized. The user-defined values that are frequently required in data science can be substituted for the null values using COALESCE. Tiffany Payne  

2. Stored Methods

We can save several SQL statements in our database for later use thanks to stored procedures. When invoked, it allows for reusability and has the ability to accept argument values. It improves performance and makes modifications simpler to implement. For instance, we’re attempting to identify all A-graded students with majors in data science. Keep in mind that CREATE PROCEDURE must be invoked using EXEC in order to be executed, exactly like the function definition. Paul Somerville 

3. Joins

Based on the logical relationship between the tables, SQL joins are used to merge the rows from various tables. In an inner join, only the rows from both tables that satisfy the specified criteria are displayed. In terms of vocabulary, it can be described as an intersection. The list of pupils who have signed up for sports is returned. Sports ID and Student registration ID are identical, please take note. Left Join returns every record from the LEFT table, while Right Join only shows the matching entries from the RIGHT table. Hamza Usmani 

4. Subqueries

Knowing how to utilize subqueries is crucial for data scientists because they frequently work with several tables and can use the results of one query to further limit the data in the primary query. The nested or inner query is another name for it. The subquery is conducted before the main query and needs to be surrounded in parenthesis. It is referred to as a multi-line subquery and requires the use of multi-line operators if it returns more than one row. Tiffany Payne 

5. Left Joins vs Inner Joins

It’s easy to confuse left joins and inner joins, especially for those who are still getting their feet wet with SQL or haven’t touched the language in a while. Make sure that you have a complete understanding of how the various joins produce unique outputs. You will likely be asked to do some kind of join in a significant number of interview questions, and in certain instances, the difference between a correct response and an incorrect one will depend on which option you pick. Tom Miller 

6. Manipulation of dates and times

There will most likely be some kind of SQL query using date-time data, and you should prepare for it. For instance, one of your tasks can be to organize the data into groups according to the months or to change the format of a variable from DD-MM-YYYY to only the month. You should be familiar with the following functions:


Olivia Tonks 

7. Procedural Data Storage 

Using stored procedures, we can compile a series of SQL commands into a single object in the database and call it whenever we need it. It allows for reusability and when invoked, can take in values for its parameters. It improves efficiency and makes it simple to implement new features. Using this method, we can identify the students with the highest GPAs who have declared a particular major. One goal is to identify all A-students whose major is Data Science. It’s important to remember that, like a function declaration, calling a CREATE PROCEDURE with EXEC is necessary for the procedure to be executed. Nely Mihaylova 

8. Connecting SQL to Python or R 

A developer who is fluent in a statistical language, like Python or R, may quickly and easily use the packages of
language to construct machine learning models on a massive dataset stored in a relational database management system. A programmer’s employment prospects will improve dramatically if they are fluent in both these statistical languages and SQL. Data analysis, dataset preparation, interactive visualizations, and more may all be accomplished in SQL Server with the help of Python or R. Rene Delgado  

9. Features of windows

In order to apply aggregate and ranking functions over a specific window, window functions are used (set of rows). When defining a window with a function, the OVER clause is utilized. The OVER clause serves dual purposes:

– Separates rows into groups (PARTITION BY clause is used).
– Sorts the rows inside those partitions into a specified order (ORDER BY clause is used).
– Aggregate window functions refer to the application of aggregate
functions like SUM(), COUNT(), AVERAGE(), MAX(), and MIN() over a specific window (set of rows). Tom Hamilton Stubber  

10. The emergence of Quantum ML

With the use of quantum computing, more advanced artificial intelligence and machine learning models might be created. Despite the fact that true quantum computing is still a long way off, things are starting to shift as a result of the cloud-based quantum computing tools and simulations provided by Microsoft, Amazon, and IBM. Combining ML and quantum computing has the potential to greatly benefit enterprises by enabling them to take on problems that are currently insurmountable. Steve Pogson 

11. Predicates

Predicates occur from your WHERE, HAVING, and JOIN clauses. They limit the amount of data that has to be processed to run your query. If you say SELECT DISTINCT customer_name FROM customers WHERE signup_date = TODAY() that’s probably a much smaller query than if you run it without the WHERE clause because, without it, we’re selecting every customer that ever signed up!

Data science sometimes involves some big datasets. Without good predicates, your queries will take forever and cost a ton on the infra bill! Different data warehouses are designed differently, and data architects and engineers make different decisions about to lay out the data for the best performance. Knowing the basics of your data warehouse, and how the tables you’re using are laid out, will help you write good predicates that save your company a lot of money during the year, and just as importantly, make your queries run much faster.

For example, a query that runs quickly but simply touches a huge amount of data in Bigquery can be really expensive if you’re using on-demand pricing which scales with the amount of data touched by the query. The same query can be really cheap if you’re using Bigquery’s Flat-rate pricing or Snowflake, both of which are affected by how long your query takes to run, not how much data is fed into it. Kyle Kirwan 

12. Query Syntax

This is what makes SQL so powerful and much easier than coding individual statements for every task we want to complete when extracting data from a database. Every query starts with one or more clauses such as SELECT, FROM, or WHERE – each clause gives us different capabilities; SELECT allows us to define which columns we’d like returned in the results set; FROM indicates which table name(s) we should get our data from; WHERE allows us to specify conditions that rows must meet for them to be included in our result set etcetera! Understanding how all these clauses work together will help you write more effective and efficient queries quickly, allowing you to do better analysis faster! John Smith 

Elevate your business with essential SQL concepts 

AI and machine learning, which have been rapidly emerging, are quickly becoming one of the top trends in technology. Developments in AI and machine learning are being seen all over the world, from big businesses to small startups.

Businesses utilizing these two technologies are able to create smarter systems for their customers and employees, allowing them to make better decisions faster.

These advancements in artificial intelligence and machine learning are helping companies reach new heights with their products or services by providing them with more data to help inform decision-making processes.

Additionally, AI and machine learning can be used to automate mundane tasks that take up valuable time. This could mean more efficient customer service or even automated marketing campaigns that drive sales growth through
real-time analysis of consumer behavior. Rajesh Namase

Author image - Ayesha
Written by Ayesha Saleem

I am a Digital Content Creator at Data Science Dojo. From years of affiliation with tech organizations, I pen down ideas, using research to benefit readers every day.

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