Oracle TO_CLOB (character) Function: A Simple Guide

The TO_CLOB (character) function in Oracle SQL is a conversion function. Its primary job is to convert various character data types—specifically those in the national character set (like NCLOB or NCHAR)—into a CLOB (Character Large Object).

A CLOB uses the standard database character set, while an NCLOB uses the national character set. This function is the standard tool for converting between them.

What is the TO_CLOB (character) Function in Oracle?

The TO_CLOB(char) function takes a character string (NCHAR, NVARCHAR2, CHAR, VARCHAR2, or NCLOB) and returns its data as a CLOB.

This is most commonly used when you need to:

• Copy data from an NCLOB column into a CLOB column.
• Standardize character data into the database character set.
• Pass a national character string to a function that only accepts CLOB.

TO_CLOB (character) Function Syntax

The syntax for TO_CLOB (character) is very simple:

TO_CLOB(char)

Let's break that down:

• char: The value or column you want to convert. This can be CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, or NCLOB.

Oracle TO_CLOB (character) Function Examples

Here are two practical examples of how to use TO_CLOB (character).

Example 1: Converting an NCHAR String to a CLOB using TO_CLOB

This example shows how to convert a simple string literal that is in the national character set (defined by the N'...' prefix) into a CLOB.

Query:

SELECT
  TO_CLOB(N'This is a sample NCHAR string.') AS "Clob_Value"
FROM DUAL;

Result: (The output will be a CLOB data type. Many SQL tools will just display (CLOB) to represent it.)

Clob_Value
----------
(CLOB)

Example 2: Updating a CLOB Column from an NCLOB Column using TO_CLOB

This is the most common use case. Imagine you have a table print_media with an NCLOB column (ad_fltextn) and a CLOB column (ad_finaltext). You need to copy the NCLOB data into the CLOB column, which requires a conversion.

Query: (This is a hypothetical UPDATE statement based on the Oracle documentation.)

-- This query reads the NCLOB data, converts it to a CLOB
-- (using the database character set), and updates the table.
UPDATE print_media
SET
  ad_finaltext = TO_CLOB(ad_fltextn)
WHERE
  product_id = 2268;

Result: (This statement would update the specified rows, performing the character set conversion.)

1 row updated.