https://www.datacamp.com/community/podcast/critical-thinking-in-data-science

<p>Debbie Berebichez, Chief Data Scientist at Metis, speaks with Hugo about what type of critical thinking skills are necessary in data science.</p>

Debbie Berebichez speaks with Hugo about the importance of critical thinking in data science.

Critical Thinking in Data Science

https://www.datacamp.com/community/blog/critical-thinking-in-data-science

https://www.datacamp.com/community/podcast/credibility-crisis-in-data-science

<p>Skipper Seabold, a Director of Data Science at Civis Analytics, discusses the current and looming credibility crisis in data science.</p>

Skipper Seabold, a Director of Data Science at Civis Analytics, discusses the current and looming credibility crisis in data science.

The Credibility Crisis in Data Science

https://www.datacamp.com/community/blog/credibility-crisis-in-data-science

https://www.datacamp.com/community/news/the-credibility-crisis-in-data-science-with-skipper-seabold-6bbmgpwy1qm

The Credibility Crisis in Data Science (with Skipper Seabold)

https://www.datacamp.com/community/news/reducing-rework-as-an-sql-data-analyst-s8wigs0qm3

In this tutorial, you will learn how to maximize your productive time in SQL.

Reducing Rework as an SQL Data Analyst

https://www.datacamp.com/community/news/sql-tutorial-how-to-write-better-queries-d2nj398ov1l

Structured Query Language (SQL) is an indispensable skill in the data science industry and generally speaking, learning this skill is fairly easy. However, most forget that SQL isn't just about writing queries, which is just the first step down the road. Ensuring that queries are performant or that 

SQL Tutorial: How To Write Better Queries

<p>By now, you know about all the benefits of SQL and are a seasoned data analyst, data engineer, or data scientist. You know about the different SQL dialects, you’re proficient in importing SQL data, and you’re fluent in writing basic SQL queries. But do you want to grow your skills to the next level? Here’s how.</p>
<h2 id="intermediate-sql-concepts">Intermediate SQL concepts</h2>
<h3 id="know-the-sql-sublanguages">Know the SQL sublanguages</h3>
<p>There are <a href="https://www.quora.com/What-are-the-SQL-sub-languages">four primary sublanguages</a> in SQL—they refer to different tasks, but are all part of the SQL language:</p>
<h4 id="1-ddl-data-definition-language-">1. DDL (Data Definition Language)</h4>
<p>These statements are used to create tables and databases and define field properties or table properties. Examples of commands in this category include CREATE, ALTER, and DROP.</p>
<h4 id="2-dml-data-manipulation-language-">2. DML (Data Manipulation Language)</h4>
<p>The statements that fall under this category are used to update data or add or remove data from tables. Commands in this category include UPDATE, DELETE, and INSERT.</p>
<h4 id="3-dcl-data-control-language-">3. DCL (Data Control Language)</h4>
<p>These SQL statements are used to control who accesses the data. The commands that fall under this category are GRANT and REVOKE.</p>
<h4 id="4-tcl-transaction-control-language-">4. TCL (Transaction Control Language)</h4>
<p>This language is used to commit data and restore data. COMMIT and ROLLBACK fall under this category.</p>
<h4 id="5-dql-data-query-language-">5. DQL (Data Query Language)</h4>
<p>This is to retrieve data from SQL server. SELECT statement falls into this category.</p>
<p>These may look intimidating, but don’t worry! SQL is a very elegant, straightforward language to learn, especially because you cannot use SQL to create data visualizations—it’s all about creating tables, organizing and cleaning data, and learning to ask the right questions.</p>
<h3 id="unions-and-joins">Unions and joins</h3>
<p>A lot of the time, the data you need will not be stored in one giant table but will be spread out across multiple tables. Using SQL, you can merge these tables together to combine all the data you need in one place. Since UNION and JOIN deal with tables, they go in the FROM statement.</p>
<p>A UNION will basically stack two tables with identical columns on top of each other. This is useful for sales transaction data that may be broken into different tables by month, quarter, or year.</p>
<p>There are several kinds of commonly used JOINS—Inner, Outer, Left, and Exception. To put it simply, these will return different combinations of rows from the tables being joined together.</p>
<p>Additional resources:</p>
<ul>
<li><a href="https://www.w3resource.com/sql/joins/sql-joins.php">SQL Joins | Mode</a></li>
<li><a href="https://www.diffen.com/difference/Inner_Join_vs_Outer_Join | Diffen">Inner vs. Outer Joins | Diffen</a></li>
</ul>

<h2 id="intermediate-sql-syntax">Intermediate SQL syntax</h2>
<p>By now, you know the basics of <a href="https://www.w3schools.com/sql/sql_syntax.asp">SQL syntax</a>, including the functions SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY, and LIMIT. You’re proficient in <a href="https://www.datacamp.com/courses/database-design">Database Design</a> and you also understand the <a href="https://www.datacamp.com/community/blog/how-to-learn-sql">SQL order of execution</a>—that queries are written differently from how they’re processed.</p>
<p>Now it’s time to learn more advanced syntax.</p>
<h3 id="aggregations-select-group-by-and-having">Aggregations: SELECT, GROUP BY, and HAVING</h3>
<p>Similar to Excel, you can use SQL to aggregate your data by sum, average, maximum, minimum, and count. Aggregations can be useful when initially exploring your data, analyzing, or when presenting it to your audience. You can do these in the SELECT statement to return a simple aggregation, or use a GROUP BY statement to create an Excel “pivot table” out of your data.</p>
<p>Using aggregations in the SELECT statement will return just a simple calculation, for instance, if you were using SUM(column_name), your query would return one value that represent all the values in that column added up.</p>
<p>You can also introduce aggregations by categorical data. For instance, if you had a table of fruit sales data across the country, you could group the sum of all sales by product type, or the average price by state. This requires a GROUP BY statement, which comes after the WHERE statement. You will need to specify the categorical column you want your aggregations to be “grouped by”, and then include those columns in your select statement as well.</p>
<p>After your data has been neatly grouped, with an aggregation paired to a categorical variable, you can then filter on those aggregations by using a HAVING statement, which comes after GROUP BY. This is useful if you wanted to narrow your query even further, for example, if you wanted to select only those fruit stores with an average sales total over $100,000.</p>
<p>Additional resources:</p>
<ul>
<li><a href="https://www.geeksforgeeks.org/sql-string-functions/">SQL | String Functions | GeeksforGeeks</a></li>
<li><a href="https://mode.com/sql-tutorial/sql-aggregate-functions/">SQL Aggregate Functions | Mode</a></li>
<li><a href="https://www.w3schools.com/sql/sql_groupby.asp">SQL GROUP BY | W3 Schools</a></li>
<li><a href="https://www.tutorialspoint.com/sql/sql-having-clause.htm">SQL HAVING | TutorialsPoint</a></li>
</ul>

<h3 id="case-statements">Case statements</h3>
<p>A SQL CASE statement is similar to an Excel IF() function—if the data in a column matches a set criteria, then return “this”. This can be useful when reclassifying quantitative data as categorical, such as when breaking down a set of values into “High”, “Medium”, or “Low”. CASE statements go in the SELECT statement.</p>
<p>See also:</p>
<ul>
<li><a href="https://mode.com/sql-tutorial/sql-case/">Case statements | Mode</a></li>
</ul>

<h3 id="subqueries">Subqueries</h3>
<p>Subqueries may be used in several different ways, but are usually found in either the FROM or the WHERE statement. They create a small, temporary table from your data that you can then use as a new table to query from in a different way.</p>
<p>See also:</p>
<ul>
<li><a href="https://www.essentialsql.com/get-ready-to-learn-sql-server-22-using-subqueries-in-the-from-clause/">Subqueries | Essential SQL</a></li>
</ul>

<h3 id="dates-and-times">Dates and times</h3>
<p>As with many other data languages, dealing with dates and times can be tricky. Sometimes dates act like “strings”, or pieces of information. Sometimes they can be treated as actual dates, with SQL syntax that can break the data down into units such as months or years. Since there are many different ways to do this, these functions are considered more advanced SQL syntax.</p>
<p>See also:</p>
<ul>
<li><a href="https://www.sqlite.org/lang_datefunc.html">Date and Time Functions | SQLite</a></li>
</ul>

<h2 id="advance-your-sql-thinking">Advance your SQL thinking</h2>
<h3 id="sql-guidelines-to-follow">SQL guidelines to follow</h3>
<p>When you’re working in the real world, business questions won’t likely translate neatly into SQL queries. That’s why you need to carefully assess what’s needed before even writing a single line of code. Here are some good guidelines to follow when practicing SQL.</p>
<h4 id="rewrite-your-business-question-as-a-comment-first">Rewrite your business question as a comment first</h4>
<p>Use code commenting to “brainstorm” your query first—what is the question you’re trying to answer? What pieces and elements do you need to focus on? This will guide your SQL query.</p>
<p>There are two kinds of commenting, inline and multi-line.</p>
<p>--Inline is just two hyphens and it lives on one line of code—good for short, quick notes</p>
<p>/*Multi-line commenting looks like this.</p>
<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;It’s good for creating banners that explain a query’s purpose, author, etc*/</p>
<h4 id="sketch-out-your-query">Sketch out your query</h4>
<p>Before you even start typing, you should figure out what pieces you’ll need for your query. You will always need a SELECT and FROM statement—but what else might you need? Do you need to filter the data using a WHERE statement? Will you need to use aggregate functions?</p>
<h4 id="understand-the-different-ways-to-achieve-your-objective">Understand the different ways to achieve your objective</h4>
<p>When possible, try to have multiple ways of doing the same thing. That way, you can quality check yourself and validate if you can get the same results. For example, you can find the highest value in a column either by using the MAX() function in the STATEMENT, or by using ORDER BY to sort the data and then LIMIT to limit so only one row is returned.</p>
<h4 id="test-your-query">Test your query</h4>
<p>Build your query one line at a time and run it frequently to check that it works. Adding pieces one at a time also helps prevent you from having to go back through your code line by line in case it doesn’t work.</p>
<h4 id="profile-your-table">Profile your table</h4>
<p>In order to start performing queries, you first must understand the data elements within it. Start out by viewing the entire database; then, a few columns at a time. Find the range of values, both categorical and quantitative, to get an idea of what information is contained in the table.</p>
<h4 id="keep-a-list-of-assumptions">Keep a list of assumptions</h4>
<p>When writing any kind of data code, you should always make a list of assumptions to easily track your limitations and dependencies.</p>
<h4 id="keep-a-data-dictionary">Keep a data dictionary</h4>
<p>Compile a central repository for the data elements you’re using, containing descriptions of the different tables and fields used within the analysis. This can include the different data types in each column (character, integer, money, date, etc), and a brief description of the column itself.</p>
<h4 id="always-allocate-time-to-perform-data-quality-checks">Always allocate time to perform data quality checks</h4>
<p>The analysis doesn’t end when you’ve finished writing your query. You still have to understand your results and perform quality checks to make sure your analysis is correct. Try different ways of achieving the same result to see if you get something different—this is another time when inline commenting comes in handy!</p>
<h3 id="practice-in-a-sandbox">Practice in a sandbox</h3>
<p>One of the best ways to learn any coding language is to find a “sandbox” to play around in. You’ll be able to test out your code, see if it runs, modify it, run it again, over and over until you feel comfortable with the coding principles and syntax. To start out, you may want a little more guidance—try finding a project with clear instructions and solution code to check your work.</p>
<p>Here are a few good practice resources:</p>
<ul>
<li><a href="https://www.hackerrank.com/domains/sql">Solve SQL | HackerRank</a></li>
<li><a href="http://sqlfiddle.com/">SQL Fiddle</a></li>
<li><a href="http://mystery.knightlab.com/">The SQL Murder Mystery | Knightlab</a></li>
</ul>

<p>That’s all for now. Hope this was useful to you—keep practicing and learning!</p>


https://www.datacamp.com/community/blog/blog-how-to-become-a-sql-expert

Here’s a comprehensive guide on more advanced SQL concepts and syntax.

How to Become a SQL Expert

<p>SQL, also known as Structured Query Language, is a powerful tool to search through large amounts of data and return specific information for analysis. Learning SQL is crucial for anyone aspiring to be a data analyst, data engineer, or data scientist, and helpful in many other fields such as web development or marketing.</p>
<p>The good news is that SQL is easy to learn online in just one or two months—many aspiring data professionals start off with SQL and then move onto more complex programming languages like Python and R. SQL has <a href="https://codingsight.com/structured-query-language-importance-of-learning-sql/">many other benefits</a>, including its flexibility to handle millions of rows of data and its universality across disciplines and industries. Data analysis done in SQL is easy to audit and replicate, especially when compared to spreadsheet tools.</p>
<p>SQL has been around since the 1970s and is here to stay. In this article, we’ll walk you through everything you need to get started in SQL.</p>
<h2 id="what-to-know-before-you-begin">What to know before you begin</h2>
<h3 id="sql-and-relational-databases">SQL and relational databases</h3>
<p>Many organizations use a relational database to store and <a href="https://www.youtube.com/watch?v=FR4QIeZaPeM">process large amounts of data</a>. With SQL (pronounced either as “sequel” or as “ess-que-ell”), you can “query,” or ask questions of, the data in a relational database. In other words, SQL is the programming language used to communicate with these databases. Each database uses its own SQL dialect but they all share the same basic syntax.</p>
<h3 id="different-sql-dialects">Different SQL dialects</h3>
<p>Although all SQL languages share a basic structure, some of the specific commands and styles can differ (kind of like how different regions of the U.S. can refer to a carbonated sugary beverage as either a “soda,” a “pop,” or a “coke”). With so many SQL dialects, <a href="https://www.datacamp.com/community/blog/sql-differences">it can be hard to know where to start</a>. Popular dialects include <a href="https://www.mysql.com/">MySQL</a>, <a href="https://www.sqlite.org/about.html">SQLite</a>, and <a href="https://www.microsoft.com/en-us/sql-server">SQL Server</a>, but we recommend starting with <a href="https://www.postgresql.org/">PostgreSQL</a>—it’s the closest to <a href="https://www.sqlstyle.guide/">standard SQL syntax</a> so it’s easily adapted to other dialects. Of course, if your company already has a database, you should learn the compatible dialect.</p>
<h2 id="4-steps-to-learn-sql">4 steps to learn SQL</h2>
<p>Learning SQL doesn’t require prior programming knowledge, so it’s great for beginners. Devote a couple of weeks to these four steps, and you’ll be on your way to your dream <a href="https://www.dataquest.io/blog/10-data-analytics-jobs/">analytics career</a>.</p>
<h3 id="1-learn-basic-sql-syntax">1. Learn basic SQL syntax</h3>
<p>You’ll need to understand the basics of <a href="https://www.w3schools.com/sql/sql_syntax.asp">SQL syntax</a>, including the functions SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY, and LIMIT. The different SQL dialects use very similar syntax, with a few exceptions.</p>
<p>With SQL, the order of written code differs from the <a href="https://www.sisense.com/blog/sql-query-order-of-operations/">order of execution</a>. So you’ll need to understand proper query structure and the order in which queries must be written.</p>
<h4 id="sql-order-of-execution">SQL Order of Execution</h4>
<center><a href="https://www.datacamp.com/"><img src="https://res.cloudinary.com/dyd911kmh/image/upload/f_auto,q_auto:best/v1602778225/SQL_order_of_execution_1_xd76fb.png" /></a></center>
<p></p>
<p>TL;DR: Your query will always need a SELECT and a FROM statement (to identify which columns you want returned from which table)—the others are optional.</p>
<h3 id="2-take-an-online-sql-course">2. Take an online SQL course</h3>
<p>You can learn how to use SQL in production even before accessing a database. The best way to learn SQL is with hands-on courses that introduce core concepts and get you familiar with SQL code. I may be biased, but DataCamp’s <a href="http://datacamp.com/courses/introduction-to-sql">Introduction to SQL</a> course is a brilliant overview—it’s the first course in our <a href="https://www.datacamp.com/tracks/sql-fundamentals">SQL Fundamentals</a> skill track. W3Schools’ <a href="https://www.w3schools.com/sql/default.asp">SQL Tutorial</a>, Codecademy’s <a href="https://www.codecademy.com/learn/learn-sql">Learn SQL</a> course, and Khan Academy’s <a href="https://www.khanacademy.org/computing/computer-programming/sql">Intro to SQL</a> are also excellent.</p>
<h3 id="3-start-practicing-with-real-data">3. Start practicing with real data</h3>
<p>The best way to master SQL is by practicing in your own environment—so you’ll need to install a database. If your company already uses a database, you should go through the proper channels to install it on your system. You (or your company) may be more comfortable working in a duplicate database that is not connected to live data at first—and that’s ok!</p>
<p>You can also install a free database, like <a href="https://www.pgadmin.org/download/">PostgreSQL (PGadmin)</a>, <a href="https://www.sqlite.org/download.html">SQLite</a>, or <a href="https://dev.mysql.com/downloads/mysql/">MySQL</a>; or follow our step-by-step tutorial on <a href="https://www.datacamp.com/community/tutorials/how-to-install-sql-server">how to install SQL Server</a>.</p>
<p>Then, you’ll need some data to play with. Preferably, you’d use real data from your company so you can start exploring data that matters to you. Alternatively, you can download a public dataset through <a href="https://www.kaggle.com/datasets">Kaggle</a> or <a href="https://github.com/freeCodeCamp/open-data">freeCodeCamp Open Data</a>.</p>
<h3 id="4-prepare-for-a-job-that-requires-sql">4. Prepare for a job that requires SQL</h3>
<p>So many roles today require SQL knowledge, and coding on a daily basis is the best way to become an expert. Before you start applying to jobs, you can plug any gaps in your SQL repertoire with DataCamp’s <a href="https://assessment.datacamp.com/data-analysis-in-sql">Data Analysis in SQL</a> skill assessment. As you’re applying to positions, make sure to <a href="https://zety.com/blog/sql-developer-resume-example">tailor your resume to the role</a> to stand out. And if you land that coveted job interview, you should know how to answer the <a href="https://www.sqlbot.co/blog/sql-interview-questions">top 13 SQL interview questions</a>.</p>
<h2 id="practice-practice-practice-">Practice, practice, practice!</h2>
<p>Learning SQL is like learning any other language—it takes constant practice to stay sharp and learn new things! Set aside some time every day or at least once a week to <a href="https://www.hackerrank.com/domains/sql">practice your SQL coding skills</a>. Keep at it and you’ll be a SQL superstar in no time!</p>


https://www.datacamp.com/community/blog/how-to-learn-sql

Here’s everything you need to know to get started in SQL.

How to Learn SQL

<h2>Retrieving Data From The Database</h2><p>This chapter provides a brief introduction to working with relational databases in a marketing context. You'll learn about their structure,  how to talk about them using database lingo, and how to begin an  analysis by using simple SQL commands to select and summarize columns  from database tables.</p><h2>Filter Data And Limit Your Output</h2><p>In this chapter, you'll learn how to filter tables for rows that satisfy your criteria of interest with the help of basic comparison operators and combinations of multiple criteria.</p><h2>What's Next?</h2><p>Besides selecting columns and filtering rows, there is much more that you can do with SQL! This chapter will present you with some examples that will motivate you to continue to develop this newly gained skill!</p>

https://www.datacamp.com/community/open-courses/sql-tutorial-for-marketers

The best marketers and growth hackers are data-driven. Learn how to use Structured Query Language (SQL) to query a database containing bank clients and marketing campaigns data.

SQL Tutorial for Marketers

<p>SQL Server is a relational database management system. One of the key principles of the relational database is that data is stored across multiple tables.</p>
<center><img src="https://res.cloudinary.com/dyd911kmh/image/upload/c_scale,f_auto,q_auto:best,w_564/v1603485855/join1_nitybm.png" /></center>

<p>We will need to be able to join tables together in order to extract the data we need. We use <code>primary</code> and <code>foreign</code> keys to join tables.</p>
<h2 id="primary-key">Primary Key</h2>
<p>A primary key is a column that is used to uniquely identify each row in a table. This uniqueness can be achieved by using a sequential integer as an identity column. Or sometimes, existing columns naturally contain unique values, and they can be used.</p>
<p>In the below example, we can see the first few rows from the <code>artist</code> table. It has two columns, <code>artist_id</code>, and <code>name</code>. The <code>artist_id</code> column acts as a primary key for this table, it is an integer column, and each value is different.</p>
<pre><code>+-----------+-------------------+
| artist_id | name              |
|-----------+-------------------|
| 1         | AC/DC             |
| 2         | Accept            |
| 3         | Aerosmith         |
| 4         | Alanis Morissette |
| 5         | Alice In Chains   |
+-----------+-------------------+
</code></pre><p>Now let&#39;s look at the <code>album</code> table. Can you spot the primary key? Yes, it&#39;s the <code>album_id</code> column. It&#39;s common for the primary key to be named &quot;table-name underscore id&quot;. But, you&#39;ll have noticed there is also an <code>artist_id</code> column. That also consists of integers and has the same name as the <code>artist_id</code> column in the artist table. What does this mean?</p>
<pre><code>+----------+-------------------------+-----------+
| album_id | title                   | artist_id |  
|----------+-------------------------+-----------|
| 1        | For Those About To Rock | 1         |
| 2        | Balls to the Wall       | 2         |
| 3        | Restless and Wild       | 2         |
| 4        | Let There Be Rock       | 1         |
| 5        | Big Ones                | 3         |
+----------+-------------------------+-----------+
</code></pre><h2 id="foreign-keys">Foreign Keys</h2>
<p>Well, from the previous output, it is clear that the <code>artist_id</code> in the artist table acts as a <code>Foreign_key</code> to the album table. The <code>FOREIGN KEY</code> constraint is used to prevent actions that would destroy links between tables.</p>
<ul>
<li><code>artist</code> table</li>
</ul>
<pre><code>+-----------+-------------------+
| artist_id | name              |
|-----------+-------------------|
| 1         | AC/DC             |
| 2         | Accept            |
| 3         | Aerosmith         |
| 4         | Alanis Morissette |
| 5         | Alice In Chains   |
+-----------+-------------------+
</code></pre><ul>
<li><code>album</code> table</li>
</ul>
<pre><code>+----------+-------------------------+-----------+
| album_id | title                   | artist_id |  
|----------+-------------------------+-----------|
| 1        | For Those About To Rock | 1         |
| 2        | Balls to the Wall       | 2         |
| 3        | Restless and Wild       | 2         |
| 4        | Let There Be Rock       | 1         |
| 5        | Big Ones                | 3         |
+----------+-------------------------+-----------+
</code></pre><p>This means that when the <code>artist_id</code> in the album table matches the <code>artist_id</code> in the artist table, those rows can be linked as a <code>JOIN</code>.</p>
<h2 id="joining-album-and-artist">Joining Album and Artist</h2>
<p>Rows 1 and 4 of the artist table have an <code>artist_id</code> of 1. The <code>artist_id</code> 1 in the artist table is AC/DC. So, when we join the two tables together, we return the album details from the album table, and the corresponding artist details from the artist table - joined using the <code>artist_id</code> field, which is common to both tables.</p>
<p>This is known as an <code>inner</code> join.</p>
<pre><code class="lang-SQL">SELECT
  album_id,
  title,
  album.artist_id,
  name AS artist_name
FROM album
INNER JOIN artist ON artist.artist_id = album.artist_id
WHERE album.artist_id = 1;
</code></pre>
<pre><code>+----------+-------------------------+-----------+-------------+
| album_id | title                   | artist_id | artist_name |
|----------+---------------------------------------+-----------|
| 1        | For Those About To Rock | 1         | AC/DC       |
| 4        | Let There Be Rock       | 1         | AC/DC       |
+----------+-------------------------+-----------+-------------|
</code></pre><p>We joined the album and artist tables by matching the <code>artist_id</code> from the artist table to the <code>artist_id</code> in the album table.</p>
<p>When selecting columns with the same name from different tables, you must fully qualify the column name. Otherwise, SQL Server will not know which table to <code>SELECT</code> the column from.</p>
<p>To fully qualify a column, you have to prefix it with the relevant table name, followed by a period.</p>
<h3 id="inner-join-syntax">Inner Join Syntax</h3>
<p>Here&#39;s a generic example to remind you of the syntax. When we select the relevant columns from the main table, <code>table_A</code> in this case, then select any additional column we want to join to, which in this case is <code>table_B</code>. Then we specify the join using the keywords <code>INNER JOIN</code> and <code>ON</code>, providing the necessary key columns from both the tables.</p>
<pre><code class="lang-sql">SELECT
    table_A.columnX,
    table_A.columnY,
    table_B.columnZ,
FROM table_A
INNER JOIN table_B ON table_B.foreign_key = table_A.primary_key;
</code></pre>
<h2 id="not-using-a-where-clause">Not Using a <code>WHERE</code> Clause</h2>
<p>In this example, we don&#39;t specify a <code>WHERE</code> clause, so we return ALL combinations of ALL matches between the artist and album tables, again, based on the <code>artist_id</code> column, which is common to both.</p>
<pre><code class="lang-SQL">SELECT
  album_id,
  title,
  album.artist_id,
  name AS artist_name
FROM album
INNER JOIN artist on artist.artist_id = album.artist_id;
</code></pre>
<pre><code>+----------+---------------------------------------+-----------+
| album_id | title                   | artist_id | artist_name |
|----------+---------------------------------------+-----------|
| 1        | For Those About To Rock | 1         | AC/DC       |
| 4        | Let There Be Rock       | 1         | AC/DC       |
| 2        | Balls To The Wall       | 2         | Accept      |
| 3        | Restless and Wild       | 2         | Accept      |
+----------+---------------------------------------+-----------+
</code></pre><h2 id="multiple-inner-join">Multiple Inner Join</h2>
<p>You can also join more than two tables using <code>INNER JOINS</code>. You simply provide an additional <code>INNER JOIN</code> for each combination of tables. In our code below, we join tables A and B, and also B and C.</p>
<pre><code class="lang-SQL">SELECT
  table_A.columnX,
  table_A.columnY,
  table_B.columnZ table_C columnW
FROM table_A
INNER JOIN table_B ON table_B.foreign_key = table_A.primary_key
INNER JOIN table_C ON table_C.foreign_key = table_B.primary_key;
</code></pre>
<p>To learn more about joining tables, please see this video from our course <a href="https://campus.datacamp.com/courses/introduction-to-sql-server/joining-tables?ex=1">Introduction to SQL Server</a>.</p>
<iframe width="560" height="315" src="https://www.youtube.com/embed/DRDFtejKZs8" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

<p>This content is taken from DataCamp’s <a href="https://www.datacamp.com/courses/introduction-to-sql-server">Introduction to SQL Server</a> course by John MacKintosh.</p>


https://www.datacamp.com/community/tutorials/sql-joins

(Tutorial) Joins in SQL

Joins in SQL

<p>SQL or structured query language is the native language for interacting with databases and is designed for exactly this purpose. It is a language of databases. A database models real-life entities like professors and universities by storing them in tables. Each table contains data from a single entity type. This reduces redundancy by storing entities only once. For example, there only needs to be one row of data containing a certain company&#39;s details. Lastly, a database can be used to model the relationship between entities.</p>
<p>If you would like to know how to learn the basics of SQL or become an expert, check out these blog posts:</p>
<ul>
<li><a href="https://www.datacamp.com/community/blog/how-to-learn-sql">How to Learn SQL</a></li>
<li><a href="https://www.datacamp.com/community/blog/blog-how-to-become-a-sql-expert">How to Become a SQL Expert</a></li>
</ul>
<h2 id="querying-databases">Querying Databases</h2>
<p>While SQL can be used to create and modify databases, this tutorial&#39;s focus will be on querying databases. A query is a request for data from a database table (or combination of tables). Querying is an essential skill for a data scientist since the data you need for your analyses will often live in databases.</p>
<p>In SQL, you can select data from a table using a <code>SELECT</code> statement. For example, the following query selects the <code>name</code> column from the <code>people</code> table:</p>
<pre><code class="lang-sql">SELECT name
FROM people;
</code></pre>
<p>In this query, <code>SELECT</code> and <code>FROM</code> are called keywords. In SQL, keywords are not case-sensitive, which means you can write the same query as:</p>
<pre><code class="lang-sql">select name
from people;
</code></pre>
<p>That said, it&#39;s good practice to make SQL keywords uppercase to distinguish them from other parts of your query, like column and table names.</p>
<p>It&#39;s also good practice to include a semicolon at the end of your query. This tells SQL where the end of your query is!</p>
<h2 id="sql-order-of-execution">SQL Order of Execution</h2>
<center><img src="https://res.cloudinary.com/dyd911kmh/image/upload/f_auto,q_auto:best/v1603483591/SQL_order_of_execution_1_xd76fb_feygfm.png" /></center>

<p>Note: Your query will always need a SELECT and a FROM statement (to identify which columns you want returned from which table)—the others are optional.</p>
<h2 id="example-of-select">Example of SELECT</h2>
<p>In the following example, you will SELECT the <code>title</code> column from the <code>films</code> table.</p>
<pre><code class="lang-sql">SELECT title
FROM films;
</code></pre>
<p>When we run the above code, it produces the following result:</p>
<center><img src="https://res.cloudinary.com/dyd911kmh/image/upload/c_scale,f_auto,q_auto:best/v1603483189/whatsql4_knglmg.png" /></center>

<p><a href="https://campus.datacamp.com/courses/introduction-to-sql/selecting-columns?ex=7">Try it for yourself</a>.</p>
<p>This content is taken from DataCamp’s <a href="https://learn.datacamp.com/courses/introduction-to-sql">Introduction to SQL</a> course by Nick Carchedi.</p>


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