Oracle ASCIISTR Function: A Simple Guide

The ASCIISTR function in Oracle SQL is a special-purpose utility that converts a string from any character set into a "safe" 7-bit ASCII representation.

Its main purpose is to make non-ASCII characters (like Ä, Ç, or ñ) "visible" by converting them into their Unicode escape sequence (e.g., \00C4).

What is the ASCIISTR Function in Oracle?

The ASCIISTR(char) function takes a string and returns a new string in the database character set.

• Any standard ASCII characters (A-Z, 0-9, !, ?, etc.) are left unchanged.
• Any non-ASCII character is converted to a \xxxx code, where xxxx is its UTF-16 code unit.

This function is not for displaying to end-users. It's a technical tool for:

• Debugging: "Seeing" hidden or un-printable characters in your data.
• Data Sanitization: Converting a string into a pure ASCII format before exporting it to a legacy system that might not support Unicode.

ASCIISTR Function Syntax

The syntax for ASCIISTR is very simple:

ASCIISTR(char)

Let's break that down:

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

Oracle ASCIISTR Function Examples

Here are two practical examples of how to use ASCIISTR.

Example 1: Converting a String with Non-ASCII Characters using ASCIISTR

This example shows the function converting a German name that contains an umlaut (Ä). The Ä is not a standard ASCII character, so it will be converted to its Unicode representation.

Query:

SELECT
  ASCIISTR('MÄLLER') AS "ASCII_String"
FROM DUAL;

Result: (The non-ASCII character Ä is converted to \00C4)

ASCII_String
------------
M\00C4LLER

Example 2: Identifying "Problem" Data using ASCIISTR

Imagine you are trying to find data that is not pure ASCII. You can compare the ASCIISTR version of a string to its original version. If they are different, you know the string contains non-ASCII characters.

Query:

WITH user_data AS (
  SELECT 'John Smith' AS name FROM DUAL UNION ALL
  SELECT 'José' AS name FROM DUAL
)
SELECT
  name,
  ASCIISTR(name) AS "Safe_String"
FROM user_data
WHERE
  name != ASCIISTR(name); -- Find only the ones that change

Result: (This query finds only the "problem" data. 'John Smith' is filtered out because ASCIISTR('John Smith') is the same as the original.)

NAME   Safe_String
----   -----------
José   Jos\00E9