BYTE vs. CHAR in Oracle Column Datatypes: What's the Difference?

Differences in BYTE and CHAR data type length qualifiers in Oracle database

When defining column data types in Oracle database, you may encounter the use of BYTE or CHAR as the character column length qualifier. There are subtle but important differences between these two qualifiers that may affect data storage and processing.

Use BYTE

When you specify BYTE as the length qualifier, you are essentially telling Oracle to allocate a specific number of bytes for each character in the column. For example, in the following statement:

<code class="language-sql">CREATE TABLE CLIENT
(
 NAME VARCHAR2(11 BYTE),
 ID_CLIENT NUMBER
)</code>

Oracle will reserve 11 bytes for each character in the NAME column. This method is suitable for storing fixed-width characters, such as those in the ASCII character set. However, if the database character set is multibyte (Unicode character sets are common), non-ASCII characters may occupy multiple bytes. This may limit the number of characters actually stored in the allocated space.

Use CHAR

Alternatively, specifying CHAR as the length qualifier indicates that Oracle should allocate enough space to store the specified number of characters, regardless of the number of bytes they may consume. This is more flexible and ensures that the column can accommodate variable length characters, as in the following example:

<code class="language-sql">CREATE TABLE CLIENT
(
 NAME VARCHAR2(11 CHAR),
 ID_CLIENT NUMBER
)</code>

Here, Oracle will allocate space to store the 11 characters in the NAME column, even though these characters require multiple bytes each. This approach ensures consistent character handling, which is critical for internationalization and multi-byte character sets.

In summary, use BYTE to specify a fixed number of bytes per character, while CHAR allows for variable length characters. The appropriate choice depends on the nature of the data being stored and the character set used.

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