Understanding SQL Data Types

This article is a complementary resource to the Learn SQL Basics course.

Understanding SQL Data Types

In SQL, data types define what kind of data can be stored in a column. Choosing the right data type is important for data accuracy, storage efficiency, and database performance.

This guide explores the different data types in SQL.

Why are Data Types Important?

Data types are crucial because they define the type of data that can be stored in each column of your table.

SQL data types help in:

Ensuring that only valid data is stored.
Optimizing storage space and query performance.
Preventing errors caused by incompatible data formats.

Common SQL Data Types

Here are some commonly used SQL data types:

Data Type	Description
INTEGER	Stores whole numbers (e.g., 5, -10, 100).
INT	Stores integer values similar to INTEGER.
VARCHAR(size)	Stores text with a defined character limit (e.g., VARCHAR(255)).
TEXT	Stores large pieces of text (string) data.
DATE	Stores data in the YYYY-MM-DD format.

Note: We've mentioned only few data types here to get a general understanding of what data types are. A database system may have many different data types.

Example: SQL Data Types

Let's try to understand data types with an example.

Suppose, a company needs to store employee details such as name, age, and date of joining.

The appropriate SQL data types for these fields are:

VARCHAR: for storing name
INT: for storing age
DATE: for storing date of joining

CREATE TABLE Employees (
    name VARCHAR(100),
    age INT,
    date_of_joining DATE
);

This ensures that names are stored as text, ages as whole numbers, and joining dates in a standard date format.

Important!

It is possible for two different database management systems to have data types with the same name, but with different behavior or properties.

For example, a DATE data type in one database system may only store the date, while in another system, it may store the date and time, along with the timezone information.

Therefore, it is important to check the specific database system's documentation to ensure that we are using the data type properly.

Now that we have a basic understanding of data types, we are ready to create tables in SQL.

Final Thoughts

Understanding data types is essential for working with databases. Using the right data type keeps your database efficient and prevents errors. As you practice SQL, you'll get more familiar with how different data types work in various systems.