Understanding SQL data types is essential for designing databases that accurately represent real-world information. SQL data types are grouped into several main categories, each tailored for specific kinds of data you might need to store. The primary categories are: numeric types, character types, date/time types, and special types.

• Numeric types handle numbers, such as a person's age or a product price. For example, you might store an employee's age as an INTEGER;
• Character types are used for text data, such as names or email addresses, and include types like VARCHAR for variable-length strings;
• Date/time types are designed for storing dates and times, such as a user's birthdate using the DATE type;
• Special types cover data that doesn't fit the other categories, such as BOOLEAN for true/false values that indicate whether a user is active.

To see how these categories work together, consider a table that tracks basic user information: age, name, birthdate, and whether the user is active.

CREATE TABLE user_overview (
    age INTEGER,
    name VARCHAR(50),
    birthdate DATE,
    is_active BOOLEAN
);

Each column in this table is chosen to match the kind of information it stores. The age column uses the numeric INTEGER type, perfect for whole numbers. The name column is a VARCHAR, a character type that can store varying lengths of text. The birthdate column is a DATE type, which is ideal for storing calendar dates. The is_active column uses the BOOLEAN special type, suited for true or false values.

These categories help you organize and validate your data efficiently. Numeric types ensure you only store numbers where appropriate, character types let you handle names and descriptions, date/time types keep track of important events, and special types like BOOLEAN allow you to represent logical states.