Oracle TO_MULTI_BYTE Function: A Simple Guide

The TO_MULTI_BYTE function in Oracle SQL is a specialized character set function. Its job is to convert single-byte (or "half-width") characters into their corresponding multibyte (or "full-width") characters.

This function is primarily used in databases that support character sets (like UTF8) that contain both single-byte and multibyte versions of the same character. This is common in East Asian language character sets (e.g., Japanese, Korean, Chinese).

What is the TO_MULTI_BYTE Function in Oracle?

The TO_MULTI_BYTE(char) function takes a string and returns a new string where any single-byte characters that have a multibyte equivalent are converted.

For example, many character sets have two versions of the letter 'A':

1. Single-byte (Half-width): 'A' (the standard ASCII character)
2. Multibyte (Full-width): 'Ａ' (a wider version used for alignment in Asian text)

TO_MULTI_BYTE converts the first form to the second. If a character has no multibyte equivalent, it is returned unchanged.

TO_MULTI_BYTE Function Syntax

The syntax for TO_MULTI_BYTE is very simple:

TO_MULTI_BYTE(char)

Let's break that down:

• char: The string or column you want to convert.

Oracle TO_MULTI_BYTE Function Examples

Here are two practical examples of how to use TO_MULTI_BYTE.

Example 1: Using TO_MULTI_BYTE to Convert a Standard ASCII Character

This example converts the standard single-byte letter 'A' into its full-width, multibyte equivalent. Since the result looks similar ('A' vs 'Ａ'), we use the DUMP function to see the underlying byte-level change.

Query:

SELECT 
  DUMP('A') AS "Single_Byte_Dump",
  DUMP(TO_MULTI_BYTE('A')) AS "Multi_Byte_Dump"
FROM DUAL;

Result: (The exact byte values depend on your database character set, but the length will change)

Single_Byte_Dump      Multi_Byte_Dump
--------------------- ------------------------
Typ=96 Len=1: 65      Typ=1 Len=3: 239,188,161

The Len=1 shows the original 'A' was 1 byte. The Len=3 shows the new 'Ａ' is 3 bytes (in this UTF8 example).

Example 2: Using TO_MULTI_BYTE on a Half-Width Katakana Character

This is a more practical example. Japanese character sets often have half-width Katakana characters (single-byte) and full-width (multibyte) versions. Let's convert the half-width 'ka' (ｶ) to its full-width カ.

We use UNISTR to provide the Unicode code for the half-width character.

Query:

SELECT 
  UNISTR('\FF76') AS "Half_Width",
  TO_MULTI_BYTE(UNISTR('\FF76')) AS "Full_Width"
FROM DUAL;

Result:

Half_Width Full_Width
---------- ----------
ｶ          カ