In this guide, we’re going to talk about what a database schema is and why they are used. We’ll also walk through an example so you can see what developers mean when they are talking about a database schema.
As you can imagine, a lot of thought goes into how a database should be structured. Before creating a database, a developer will plan out what that database should include and how different parts of the database will link together. Planning in advance helps ensure that a database contains all the necessary components to cover the needs of a project.
In software development, coders use database schemas to plan out how a database should be configured. These documents, termed “schema”, are then used to implement the design of a database.
What Is a Database Schema?
A database schema is used to outline the architecture of a database, and it will help ensure the following:
- Consistent formatting of data entries
- All record entries have a unique primary key
- No important data is omitted
Depending on the project, databases can get very large with vast amounts of data very quickly. Suppose you are building a content management system database.
That database may start out with two tables: users and content. As you add more features to your project, you may add tables for different post types, and more. This introduces new layers of complexity into a database.
That’s where database schemas come in. Developers will produce a schema at the start of a project which provides a graphical view of the database they are going to create. This schema will group all the tables that a database will store and its fields together. In other words, a single schema defined the structure of a database.
Who Creates Database Schemas?
Schemas are an essential part of database management systems. In smaller projects, database schemas are usually written by the developers who will be working on the project. This is because they are most likely to have intimate knowledge of how the project will work.
For larger projects, a database developer or designer may be put in charge of developing the database schema for a project. These developers and designers work with databases all day. So, they have both a broad and detailed perspective on how a database is constructed.
What Does a Database Schema Include?
Database schemas include data on all the objects in a database, such as fields, tables, and relations. A schema may also outline triggers, views, and indexes.
Take the following example:
This is a single schema that contains the structure of two tables: User and Post. There are a few pieces of information contained within this schema:
- Titles of our table names (User and Post)
- Fields each table contains (i.e. “id”, “name”, and “email”)
- Data type of each field (i.e. BOOL or VARCHAR)
- Functions that will be applied to each post (i.e. createPost). These may not be defined in the database, but allow developers to see what actions will be performed on each particular field.
- Relations between tables (i.e. a Post must be linked to a User)
All of this information is useful to a developer who is working on a project. When a developer has a query about the structure of a database, they only need to look at the schema. Schemas may also outline the users who have been granted access to particular tables in the database.
“How many tables does this database contain?” “What fields does the Post table use?” “Does the User table have an ‘is_verified’ field?” These are all questions that a developer could answer based solely on the contents of the graphic above.
You may also hear schemas being used to describe the general structure of a database. Often, when a schema is implemented, developers will refer to the structure of a database as its “schema”.
CREATE TABLE user ( id integer NOT NULL AUTO_INCREMENT, name VARCHAR(50) NOT NULL, email VARCHAR(50) NOT NULL, is_admin BOOL NOT NULL UNIQUE KEY(id) );
While most developers working with SQL will understand this command, it’s quite difficult to read. On the other hand, database schemas are easier to read.
Database Instances vs. Database Schemas
What is the difference between a database instance and a schema?
A schema is the outline of a database. It is represented in a graphic format, like our example from earlier. Schemas do not contain any data.
One way to think about a schema is that it is a blueprint for a database. The database hasn’t been built yet—or is still being built—and the blueprint guides the development team in creating the database.
A database instance is a hosted version of a database. For instance, the Career Karma blog has a database instance that stores all of our posts, such as this article. Database instances can change over time as their contents change, whereas database schemas usually remain the same.
With that said, a database schema may be updated as new features are requested for a software project. Making changes to a schema typically involves the work of both developers and database administrators. Developers will produce the requirements for a change to a database, and database administrators will implement those changes.
Why Are Database Schemas Important?
Database schemas are important because they help developers visualize how a database should be structured. A project may only use a few tables and fields. Still, having a schema gives developers a clear point of reference about what tables and fields a project contains. When a developer has a question, they can point to the schema.
That’s not the only reason schemas are important. Developers and database administrators rely on schemas to make sure that a database is planned out well before implementation.
This is particularly important because once a schema is implemented, it can be difficult to make changes. Once data has been moved into a table, making changes becomes even more complex. Producing a schema makes everyone involved with a project ask: what does this project need, and what does this project not need? This can reduce the need for changes to be made to a database once it has been implemented.
A database schema is a visual that outlines the architecture of a database. It contains a list of tables, the fields those tables contain, database users, stored procedures, and other pieces of information about a database. For instance, a schema may include database links, events, and indexes.
Database schemas help administrators and developers understand how a database is structured. This allows them to more effectively build on top of and manage a database.
While these schemas can change, they are usually developed at the design stage and will not change much after implementation. This is because database schemas are difficult to alter, especially when data is stored within a table.