Category: SQL

Understanding Julian Day

Posted on by Ian

Julian day is a concept you might occasionally encounter in SQL code or database operations, particularly when working with date and time functions. While it may seem esoteric at first, understanding Julian day can be incredibly useful for handling date calculations, especially in fields like astronomy, data analysis, and historical research.

This article looks at the origins, calculations, and practical applications of Julian day, including examples of converting between Julian day and other date formats in SQL.

Continue reading →

Column Constraints vs Table Constraints in SQL: What’s the Difference?

Posted on by Ian

In relational database management systems (RDBMSs), constraints are nifty tools that we can use to ensure the integrity, accuracy, and reliability of the data stored in our database.

Constraints can enforce rules at the column and table levels, guiding how data can be inserted, updated, or deleted. Whether you’re defining the uniqueness of a value, establishing relationships between tables, or ensuring that critical fields are never left blank, constraints play an important role in the design of relational databases.

Continue reading →

Understanding the Different Types of Keys in SQL

Posted on by Ian

Probably the most widely known key type in SQL is the primary key, which is chosen to uniquely identify each row in a table. Perhaps next is the foreign key, which is used to establish a relationship between tables.

But there are more key types than this, and the differences between them can be subtle, but important. Here we’ll look at nine of the various key types in SQL.

Continue reading →

JOIN ON vs USING vs NATURAL JOIN: What’s the Difference?

Posted on by Ian

Probably the most common way to join tables in SQL is with the ON clause. But that’s not the only way.

We can also join with the USING clause, which can be more concise, while providing the same or similar results. And there’s also the concept of a natural join, which is more concise again.

Let’s take a look at these three join options and compare them side by side.

Continue reading →

7 SQL Statement Examples for Beginners

Posted on by Ian

SQL (Structured Query Language) is the standard language for managing and manipulating relational databases. Whether you’re just starting your journey in data management or looking to refresh your skills, understanding the basic SQL statements is crucial.

This article will walk you through seven fundamental SQL statement examples that are pretty much standard across most major Relational Database Management Systems (RDBMSs).

Continue reading →

SQL Joins with the USING Clause: How It Compares to the ON Clause

Posted on by Ian

Perhaps one of the lesser-known clauses when it comes to SQL joins is the USING clause. While the more widely-used ON clause allows us to explicitly specify join conditions, the USING clause simplifies the syntax when the join is based on columns with the same name in both tables.

In this article, we’ll dive into the USING clause, compare it to the ON clause, and look at examples that illustrate the difference.

Continue reading →

A Comparison of 6 SQL Rank Functions

Posted on by Ian

SQL rank functions can be handy things to have when analysing data. Most major RDBMSs implement a similar bunch of ranking functions, usually with the same names. These rank functions allow us to assign rankings to rows based on specific criteria.

In this article, we’ll look at six commonly used SQL ranking functions, and observe how they differ. We’ll throw them all together into a single query and see their results side by side.

The rank functions in question are: ROW_NUMBER(), RANK(), DENSE_RANK(), NTILE(), PERCENT_RANK(), and CUME_DIST().

Continue reading →

Understanding Common Table Expressions (CTEs): A Beginner’s Guide

Posted on by Ian

Common table expressions (CTEs) are a feature that we can use in SQL to help simplify complex queries and enhance readability. They can help with things like code readability, performance, recursive queries, and more.

This article explores what CTEs are, their syntax, types, use cases, and best practices, along with examples to help illustrate their usage.

Continue reading →

Understanding SQL Data Types: A Comprehensive Guide

Posted on by Ian

Structured Query Language (SQL) is the backbone of relational database management systems (RDBMSs), enabling users to query, manipulate, and define data. One of the most fundamental concepts in SQL, and one that all SQL developers should understand, is the data type.

Whenever we create a column in SQL, we must define its data type. Similarly, when we create a variable, we define its data type.

So, why is the data type so important? Let’s find out.

Continue reading →