Oracle TO_NCLOB Function: A Simple Guide

The TO_NCLOB function in Oracle SQL is a conversion function. Its primary job is to convert various character data types (like CHAR, VARCHAR2, or CLOB) into an NCLOB (National Character Large Object).

An NCLOB is a data type designed to hold very large amounts of text (gigabytes) in the national character set (which is often a Unicode standard like UTF-16). This function is the standard way to move data into that data type.

What is the TO_NCLOB Function in Oracle?

The TO_NCLOB(char) function takes a character string (CHAR, VARCHAR2, CLOB, etc.) and returns its data as an NCLOB.

This is most commonly used when you need to:

• Copy data from a standard CLOB or VARCHAR2 column into an NCLOB column.
• Ensure that a string is stored using the national character set, which is ideal for supporting multiple languages and special Unicode characters.

This is the opposite of the TO_CLOB(character) or TO_CHAR(character) functions, which convert from the national character set.

TO_NCLOB Function Syntax

The syntax for TO_NCLOB is very simple:

TO_NCLOB(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_NCLOB Function Examples

Here are two practical examples of how to use TO_NCLOB.

Example 1: Converting a String to NCLOB using TO_NCLOB

This example shows how to convert a simple VARCHAR2 string literal into an NCLOB data type.

Query:

SELECT
  TO_NCLOB('This is a standard string.') AS "Nclob_Value"
FROM DUAL;

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

Nclob_Value
----------
(NCLOB)

Example 2: Inserting Data into an NCLOB Column using TO_NCLOB

This is the most common use case. You have a table with an NCLOB column and you want to INSERT a standard text string into it. You must use TO_NCLOB to convert the string first.

Query: (This example assumes you have a table print_media with an NCLOB column ad_fltextn.)

-- This query inserts a standard VARCHAR2 string
-- into an NCLOB column by converting it first.
INSERT INTO print_media (product_id, ad_id, ad_fltextn)
VALUES (
  3502, 
  31001, 
  TO_NCLOB('Placeholder for new product description')
);

Result: (This statement inserts the row, and the text is now stored as an NCLOB.)

1 row created.