Category: SQL

What is a Natural Key in SQL?

Posted on by Ian

In relational database design, the concept of a “key” is fundamental. Keys are essential for uniquely identifying records in a table, ensuring data integrity, and facilitating efficient data retrieval. Among the different types of keys used in SQL, the natural key is one that often sparks discussion among database designers, especially when compared with the surrogate key.

Let’s explore the concept of a natural key, its advantages and disadvantages, and look at a practical example to illustrate its use.

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SQL Atomicity Explained: The Basics of Atomic Operations

Posted on by Ian

One of the core principles that ensure data integrity in relational database management systems (RDBMSs) is atomicity. When dealing with SQL, understanding what “atomicity” and “atomic” means can help you design more reliable and robust databases.

Atomicity is a key concept that underpins how SQL transactions operate, ensuring that either all steps in a transaction are completed successfully, or none are. This article looks at the meaning of atomic in SQL, its importance, and how it fits into the broader context of database management.

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SQL CASE Examples with Multiple Conditions

Posted on by Ian

The SQL CASE statement is a handy tool that allows us to add conditional logic to our queries. It’s particularly useful when we need to categorize or transform data based on multiple conditions.

In this article, we’ll explore how to use the CASE statement with multiple conditions, providing simple examples that should work across most major relational database management systems (RDBMSs).

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How to Update Multiple Columns in SQL with a Subquery

Posted on by Ian

In SQL, it’s not unusual to see subqueries in SELECT statements, where they can help narrow down the results based on a complex condition.

But the SELECT statement isn’t the only place we can put a subquery.

We can use subqueries in an UPDATE statement, and we can update multiple rows too, if required.

In this article, we look at how to update multiple columns by using a SQL subquery in the UPDATE statement.

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What is a Composite Index in SQL?

Posted on by Ian

When looking at ways to fix slow running SQL queries, one of the first things we might do is look at what indexes are available to support the query. If none are available, then we might look at creating one. And if there is an index, perhaps it doesn’t cater for the query as well as it could.

Indexes are often created on a single column, but this isn’t the only way to create an index. We can also create indexes on multiple columns. These are typically known as composite indexes.

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Understanding the Correlated Subquery in SQL

Posted on by Ian

When writing SQL queries, we sometimes find ourselves including a subquery in the query in order to get the results we want. Sometimes the subquery we include could be taken out of that query and run by itself to return its own independent result set. But not the correlated subquery.

A correlated subquery relies on the outer query for its data. We can’t simply move it outside of the outer query and expect it to work.

Let’s take a look the correlated subquery in SQL and observe it in action with a few examples.

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The Difference Between INNER and LEFT JOINs in SQL

Posted on by Ian

SQL joins are fundamental operations in relational databases, allowing us to combine data from multiple tables. Two of the most commonly used join types are INNER JOIN and LEFT JOIN. Understanding the difference between these joins is crucial if you intend to use joins in your queries.

In this article, we’ll look at the difference between the INNER JOIN and LEFT JOIN using a simple example.

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