Oracle TO_CHAR (bfile|blob) Function: A Simple Guide

The TO_CHAR (bfile|blob) function in Oracle SQL is a special conversion function. Its job is to read binary data from a BFILE (an external file) or a BLOB (an internal binary object) and convert it into a readable text string (VARCHAR2).

This function is not for converting things like images or audio files. It is specifically designed for cases where text (like a small text file or a log message) has been stored in a binary data type, and you need to read that text back in SQL.

Important Limitation: This function returns a VARCHAR2. This means it can only handle a limited amount of data (e.g., 4000 or 32767 bytes, depending on your database settings). If the BLOB or BFILE is larger than what VARCHAR2 can hold, the data will be truncated, and you will only get the beginning of the text.

What is the TO_CHAR (bfile|blob) Function in Oracle?

The TO_CHAR(binary_value, [csid]) function takes a BFILE or BLOB and interprets its raw bytes as text, returning a VARCHAR2 string.

• Input: A BLOB or BFILE value or column.
• Output: A VARCHAR2 text string.
• csid (Character Set ID): An optional number that specifies the character set of the source binary data. If omitted (or set to 0), Oracle assumes the data is in the default database character set.

TO_CHAR (bfile|blob) Function Syntax

The syntax for TO_CHAR (bfile|blob) is:

TO_CHAR(bfile_or_blob_value, [csid])

Let's break that down:

• bfile_or_blob_value: The BFILE or BLOB column or value you want to convert to text.
• [csid] (Optional): A numeric Character Set ID. For example, 873 is often used for WE8ISO8859P1 (a common Latin-1 set).

Oracle TO_CHAR (bfile|blob) Function Examples

Because this function operates on BLOBs and BFILEs, these examples are hypothetical and assume you have tables containing these data types.

Example 1: Converting a BLOB to Text using TO_CHAR (Default Character Set)

Imagine you have a table app_logs with a BLOB column named log_content that stores error messages as text. Since the application and database use the same character set, you can omit the csid.

Query:

-- This query reads the binary data from the BLOB
-- and converts it to a readable VARCHAR2 string.
SELECT 
  log_id,
  TO_CHAR(log_content) AS "Log_Message"
FROM 
  app_logs
WHERE 
  log_id = 90210;

Result:

    LOG_ID Log_Message
---------- --------------------------------------------------
     90210 ERROR: User 123 failed to update profile.

Example 2: Converting a BFILE with a Specific Character Set using TO_CHAR

Imagine you have a table media_tab with a BFILE column media_col that points to an external text file. You know this file was saved using the WE8ISO8859P1 character set, which has an ID of 873.

Query:

-- This query tells TO_CHAR to interpret the external file's
-- bytes using character set 873.
SELECT 
  TO_CHAR(media_col, 873) AS "File_Contents"
FROM 
  media_tab
WHERE 
  file_name = 'report.txt';

Result: (The function reads the external file, translates its text from the specified character set, and returns it as a standard VARCHAR2 string.)

File_Contents
--------------------------------------------------
This is the content of the external file.