Tag: database terms

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.

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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.

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What is a Junction Table in SQL?

Posted on by Ian

A junction table, also known as an associative table or a bridge table, is a table used to manage many-to-many relationships between two other tables in a relational database.

In SQL, many-to-many relationships cannot be directly implemented using just two tables because each table’s foreign key can only relate to one other table’s primary key. Instead, a junction table is created to “link” the two tables together.

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What is an ER Diagram?

Posted on by Ian

An entity relationship (ER) diagram (also known as an ERD for Entity-Relationship Diagram) is a visual representation of the relationships between entities within a system. ER Diagrams are often used when designing relational databases. An ERD serves as a blueprint for designing a database by depicting entities, their attributes, and the relationships between them.

ER diagrams help in conceptualizing the structure of a database and serve as a communication tool between database designers, developers, and stakeholders.

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What Does Deterministic Mean in SQL?

Posted on by Ian

In SQL, a deterministic expression or function always returns the same result when given the same input. Conversely, a nondeterministic expression or function may return different results even with the same input due to factors like system time, randomization, or external data changes.

Below is a quick overview of the differences between deterministic and nondeterministic functions/expressions.

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How SQL Constraints Work: A Beginner’s Overview

Posted on by Ian

Constraints are an important concept in relational database management systems (RDBMSs). Whenever we design a database, we need to ensure that it will be able to enforce data integrity, by checking or restricting what the user can enter to only data that conforms to the rules of the database. That’s where a constraint can help.

This article explores what SQL constraints are, the various types available, their importance, and how they are implemented.

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What is User-Defined Integrity?

Posted on by Ian

Maintaining data integrity is critical for ensuring the accuracy, consistency, and reliability of data inside a relational database. Among the various strategies to enforce data integrity, user-defined integrity plays a significant role, especially in customized applications and systems where standard integrity constraints may not suffice.

This article explores the concept of user-defined integrity, its importance, how it is implemented, and scenarios where it can become essential.

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What is a One-To-One Relationship?

Posted on by Ian

In relational databases, a one-to-one relationship is a relationship between two tables where each record in the first table corresponds to one and only one record in the second table, and vice versa.

This kind of relationship is less common compared to other relationship types, but it can be useful in certain scenarios. The one-to-many and many-to-many relationships are much more common than the one-to-one relationship in SQL.

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Understanding the NOT NULL Constraint in SQL

Posted on by Ian

In SQL, constraints are essential for maintaining data integrity and ensuring the accuracy and reliability of the data stored within a database. One of the most commonly used constraints in SQL databases is the NOT NULL constraint.

In this article, I provide a quick overview of the NOT NULL constraint, its purpose, syntax, usage, and practical examples.

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