A character data type, often represented by CHAR, is a fundamental data type used in databases and programming languages to store textual information.
Specifically, according to IBM documentation, the CHAR data type is used to store character data in a fixed-length field. This data can be a string of single-byte or multibyte letters, numbers, and other characters that are supported by the code set of your database locale.
Understanding the Basics
Character data types are designed to hold sequences of characters. Unlike numerical data types that store numbers for calculations, character data types store text for display, storage, and manipulation as strings.
The most common variants include:
- CHAR: Fixed-length character string.
- VARCHAR: Variable-length character string.
This answer focuses primarily on the CHAR type as described in the provided reference.
The CHAR Data Type: Fixed-Length Storage
The defining characteristic of the CHAR data type is its fixed length. When you define a column as CHAR(n), where n is the specified length, the database will always reserve n bytes (or characters, depending on the specific database implementation and character set) for that field, regardless of the actual length of the data inserted.
Key Points about CHAR:
- Fixed Length: Every value stored occupies the exact declared length.
- Padding: If the data inserted is shorter than the defined length, it is typically padded with spaces to fill the remaining space.
- Data Content: As noted in the reference, it can store letters, numbers, and other characters.
- Encoding Dependency: The characters supported depend on the code set of your database locale. This determines whether it stores single-byte or multibyte characters.
Why Use CHAR?
While VARCHAR is more flexible for variable-length strings, CHAR can be more efficient for storing data that is consistently the same length, such as:
- Country codes (e.g., 'US', 'GB')
- State abbreviations (e.g., 'CA', 'NY')
- Fixed-length identifier codes
It can also offer slight performance advantages in some database systems due to the predictable storage size.
Example: Using CHAR
Let's consider a simple database table storing customer information.
CREATE TABLE Customers (
CustomerID INT PRIMARY KEY,
FirstName VARCHAR(50),
LastName VARCHAR(50),
StateCode CHAR(2) -- Using CHAR for fixed-length state codes
);In this example, the StateCode column is defined as CHAR(2).
Data Storage Illustration
| StateCode | Stored Data | Actual Storage | Notes |
|---|---|---|---|
| 'CA' | 'CA' | 'CA' | Exact match to length |
| 'NY' | 'NY' | 'NY' | Exact match to length |
| 'FL' | 'FL' | 'FL' | Exact match to length |
Note: While the reference mentions padding, modern SQL implementations often handle padding differently (sometimes padding with spaces on insertion and trimming on retrieval) or specify padding behavior clearly. The core concept is the reserved fixed space.
Character Support and Database Locale
The reference highlights that the types of characters CHAR can store depend on the code set of your database locale.
- Code Set: Defines the mapping between character codes and their representation. Common code sets include ASCII, UTF-8, etc.
- Database Locale: A set of environmental variables that specify cultural conventions, including the code set used for data storage and processing.
This means that a CHAR column in a database configured with a single-byte ASCII code set will behave differently (e.g., regarding maximum string length in bytes) compared to one using a multibyte UTF-8 code set, which can store a wider range of characters from different languages.
In summary, the character data type, specifically CHAR, is a fixed-length container for text data, whose capabilities are influenced by the database's character encoding settings.
