NCHAR data type

The Oracle NCHAR data type is used to store fixed-length Unicode character strings. It is specifically designed to handle characters from multiple languages and character sets, supporting national character sets. The NCHAR data type stores characters in a fixed-length format and is used when you need to store Unicode data that requires a fixed size.

Here are the detailed notes on the Oracle NCHAR data type:

1. Definition of NCHAR

• NCHAR stands for National Character Set (Fixed-Length).
• It is used to store fixed-length Unicode character data, typically used for storing multi-byte character sets or national characters.
• The NCHAR data type is similar to the CHAR data type but differs in that it is designed to store Unicode characters using national character sets like AL16UTF16, which can store characters from many different languages.

2. Syntax for NCHAR

The syntax for defining a column of type NCHAR is as follows:

NCHAR(n)

Where:

• n is the length of the string in characters, not bytes (so you define how many characters you want to store in a fixed length).

Example:

CREATE TABLE employees (

    employee_id NUMBER,

    name NCHAR(50)

);

Here, name is a fixed-length Unicode string with a length of 50 characters.

3. Characteristics of NCHAR

• Fixed-Length: Unlike VARCHAR2, which is variable-length, NCHAR always stores a string with a fixed length. If the stored string is shorter than the defined length, it will be padded with spaces.
• Storage: NCHAR stores each character in a fixed size, which is dependent on the character encoding being used. For example, in AL16UTF16 encoding (a commonly used Unicode encoding), each character typically requires 2 bytes, although it can vary for some characters.
• Unicode Compatibility: Since NCHAR stores Unicode data, it is used for storing characters from international languages, such as Chinese, Japanese, or Arabic, in a consistent format.

4. When to Use NCHAR

You should use NCHAR in the following situations:

• Fixed-Length Unicode Data: When you need to store fixed-length character data in Unicode encoding. For example, when you're working with multi-byte characters from various languages and want to ensure that the length is consistent.
• National Character Sets: If you want to use a national character set (like AL16UTF16), NCHAR is the correct choice. It is designed for storing text that uses these types of character sets.

5. Length of NCHAR

• The maximum length of NCHAR is 2000 characters. Unlike VARCHAR2, where you specify the maximum length in bytes, NCHAR uses characters as its unit of length.

For example:

CREATE TABLE products (

    product_id NUMBER,

    product_name NCHAR(100)

);

Here, product_name will always store exactly 100 characters, and if the string inserted is shorter, it will be padded with spaces.

6. Comparison of NCHAR and CHAR

• CHAR is a fixed-length character data type that stores characters using the database character set (which could be non-Unicode or an ASCII-compatible character set).
• NCHAR is also fixed-length but stores characters using the national character set (which is often Unicode). Therefore, NCHAR is used for multilingual data, ensuring proper handling of non-Latin characters like those used in Chinese, Japanese, etc.

7. Difference Between NCHAR and VARCHAR2

• Length:
• NCHAR is fixed-length, so if the data is shorter than the defined size, it is padded with spaces.
• VARCHAR2 is variable-length, meaning it only uses the space needed for the actual data and does not pad with spaces.
• Character Set:
• NCHAR is used to store Unicode data (national character set), which can handle characters from multiple languages.
• VARCHAR2 stores characters using the database's default character set, which might not support as many languages as NCHAR.

8. Storage Requirements

• The storage requirement for NCHAR depends on the national character set being used. In the case of the default Unicode character set AL16UTF16, each character is typically stored as 2 bytes.

For example:

CREATE TABLE customers (

    customer_id NUMBER,

    customer_name NCHAR(100)

);

• Here, customer_name will require 100 * 2 bytes = 200 bytes of storage (if using AL16UTF16), regardless of the actual length of the data stored (because it's fixed-length).

9. Handling NULL Values in NCHAR

• Just like other Oracle data types, NCHAR can store NULL values.
• When inserting a NULL into an NCHAR column, no space is allocated for the value.

10. When Should I Avoid Using NCHAR?

You should consider avoiding NCHAR in the following situations:

• Variable-Length Data: If the data you are storing is of variable length, use VARCHAR2 instead. NCHAR is not efficient for variable-length data because it always reserves space for the full defined length, padding with spaces as needed.
• Data Not Requiring Unicode: If you're not storing Unicode characters (i.e., if your data is in a single-byte character set like ASCII), using NCHAR is not necessary. In that case, a CHAR column would be more appropriate.

11. Examples of NCHAR Usage

Example 1: Creating a Table with NCHAR

CREATE TABLE users (

    user_id NUMBER,

    username NCHAR(20),

    country NCHAR(50)

);

• Here, username and country are fixed-length columns that will always store exactly 20 and 50 characters, respectively.

Example 2: Inserting Data into NCHAR Columns

INSERT INTO users (user_id, username, country)

VALUES (1, 'JohnDoe', 'United States');

• In this case, username will be stored as a 20-character string (padded with spaces if necessary), and country will be stored as a 50-character string.

Example 3: Selecting Data from NCHAR Columns

SELECT username, country FROM users;

• When retrieving data from an NCHAR column, Oracle will return the exact length of the string (including any trailing spaces). If you want to remove trailing spaces, you can use TRIM() or RTRIM() functions.

Example:

SELECT RTRIM(username) AS username, RTRIM(country) AS country FROM users;

12. Behavior of NCHAR in Queries

• Trailing Spaces: Since NCHAR is a fixed-length data type, it pads data with spaces. When comparing two NCHAR values, trailing spaces are significant. For example:

·        SELECT * FROM users WHERE username = 'JohnDoe   ';  -- matches only if exactly 20 characters, including spaces

13. Performance Considerations

• Since NCHAR is fixed-length, it may offer some performance benefits in specific scenarios where the length of the data is consistent, and the data is highly localized (e.g., a set of records that only require a fixed length of Unicode characters).
• However, it might be less efficient than VARCHAR2 in cases where the string lengths vary, as it uses fixed storage space even for shorter strings.

14. When to Use NCHAR

• Use NCHAR when:
• You need to store Unicode characters (such as multilingual data) in a fixed-length format.
• You want to ensure consistent string length and avoid issues with character encoding.
• You are dealing with national character sets like AL16UTF16.

15. Character Set Considerations

• NCHAR uses the national character set, which typically defaults to AL16UTF16 (a Unicode character set).
• You can change the national character set at the database level if needed.

16. Summary

• NCHAR is a fixed-length Unicode character data type used to store text data in national character sets (like Unicode).
• It is useful when you need to store multilingual or Unicode characters in a fixed-length format.
• Use NCHAR when your data is of fixed length and involves multiple character sets or national languages.
• Consider alternatives like VARCHAR2 for variable-length data that doesn't require fixed-length storage.