Tag: what is

Aggregating Data in SQL with the GROUP BY and HAVING Clauses

Posted on by Ian

When writing queries in SQL, we sometimes need to summarize data based on specific criteria. Fortunately SQL makes this easy to achieve with the GROUP BY and HAVING clauses. These two clauses allow us to aggregate data and filter the results based on group conditions.

More specifically, GROUP BY allows us to group the results, and HAVING is an optional clause that we can use to filter the results based on certain conditions.

Below is an example of where we can use these two clauses to aggregate data and filter it based on certain criteria.

Continue reading →

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.

Continue reading →

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.

Continue reading →

Understanding the ON DELETE SET DEFAULT Option in SQL Server

Posted on by Ian

In SQL Server, foreign keys are essential for maintaining referential integrity between tables. When setting up a foreign key, we have various options for handling actions when the referenced data is deleted. One of these options is ON DELETE SET DEFAULT.

This feature can be particularly useful in scenarios where it’s important to maintain the relationship while ensuring that the foreign key column doesn’t end up with invalid or null values.

Continue reading →

Using ON DELETE SET NULL for Foreign Keys in SQL Server

Posted on by Ian

When creating a foreign key constraint in SQL Server, we have the option of including ON DELETE SET NULL in the definition. When we use this option in a foreign key, it tells SQL Server to automatically set the foreign key column values to NULL in the child table when the corresponding primary key record in the parent table is deleted.

Continue reading →

Understanding PostgreSQL’s FILTER Clause

Posted on by Ian

When using aggregation functions in PostgreSQL, we have the option of including a FILTER clause. This clause allows us to narrow down – or filter – the rows that are fed to the aggregate function.

This can be be a handy way to provide functionality that we might otherwise need to use a CASE statement or perhaps a CTE.

In this article, we’ll take a look at PostgreSQL’s FILTER clause, and see how it can simplify our SQL queries by replacing CASE statements with more concise code.

Continue reading →

What is Entity Integrity?

Posted on by Ian

When working with relational databases, data accuracy and consistency are paramount. When we talk about maintaining the integrity of the data within a relational database, several types of integrity come into play. One of the most fundamental is entity integrity.

This concept is crucial for ensuring that each record within a database table is uniquely identifiable, which in turn supports the reliability of the data. In this article, we will delve into what entity integrity is, why it matters, and how it is implemented in practice. We’ll also look at an example to clarify the concept further.

Continue reading →

Understanding Fillfactor in SQL Server

Posted on by Ian

One of the various options we have when creating or rebuilding indexes in SQL Server is specifying a fillfactor. If we create or rebuild an index without specifying a fillfactor, then the default fillfactor is applied.

In some cases, using the default fillfactor may be fine, even ideal. In other cases it could be less than ideal, even terrible.

Let’s look at what fillfactor is, how it works, and how we can use it to enhance database performance.

Continue reading →