Oracle VALIDATE_CONVERSION Function: A Simple Guide to Safely Test Data

The VALIDATE_CONVERSION function in Oracle SQL is a powerful "safety check" function. Its one and only job is to test if a value (like a text string) can be successfully converted to a specific data type (like a NUMBER or DATE) without actually performing the conversion and, most importantly, without raising an error.

This is the "look before you leap" function. It's essential for cleaning and validating messy data before you try to process it.

What is the VALIDATE_CONVERSION Function in Oracle?

The VALIDATE_CONVERSION function takes a value and a target data type and returns a number:

• 1 if the conversion is successful (or if the input value is NULL).
• 0 if the conversion fails.

This is different from TO_NUMBER or TO_DATE, which will stop your entire query with an error if they find "bad" data (like the string 'N/A'). You can use VALIDATE_CONVERSION in a WHERE clause to find all the "bad" rows first, so you can fix them.

VALIDATE_CONVERSION Function Syntax

The syntax for VALIDATE_CONVERSION is as follows:

VALIDATE_CONVERSION(expr AS type_name [, fmt] [, 'nlsparam'])

Let's break that down:

• expr: The value or column you want to test (e.g., '123', '20-NOV-2025').
• AS type_name: The target data type you are testing for (e.g., AS NUMBER, AS DATE, AS TIMESTAMP).
• [fmt] (Optional): The "format model" (just like in TO_DATE or TO_NUMBER) that Oracle should use for the test. This is often required for dates or complex numbers.
• [nlsparam] (Optional): A string that specifies language settings, such as for month names.

Oracle VALIDATE_CONVERSION Function Examples

Here are two practical examples of how to use VALIDATE_CONVERSION.

Example 1: Finding Bad Numeric Data using VALIDATE_CONVERSION

This is a very common use case. Imagine you have a VARCHAR2 column that should contain numbers, but it has some bad data like 'N/A'. You can use VALIDATE_CONVERSION to find the rows that are not valid numbers.

Query:

-- This query simulates a messy data table
WITH messy_data AS (
  SELECT '123.45' AS price_text FROM DUAL UNION ALL
  SELECT '500' AS price_text FROM DUAL UNION ALL
  SELECT 'N/A' AS price_text FROM DUAL UNION ALL
  SELECT 'Call Us' AS price_text FROM DUAL
)
SELECT 
  price_text,
  VALIDATE_CONVERSION(price_text AS NUMBER) AS "Is_Valid_Number"
FROM messy_data;

Result: (The function returns 1 for the valid numbers and 0 for the invalid text.)

PRICE_TEXT Is_Valid_Number
---------- ---------------
123.45                   1
500                      1
N/A                      0
Call Us                  0

Example 2: Validating DATE Strings using VALIDATE_CONVERSION

This example shows how to validate date strings. To do this correctly, you must provide a format model (fmt) that matches the strings you are testing.

Query:

-- We will test a valid date, an impossible date (Feb 30th),
-- and a text string.
WITH event_dates AS (
  SELECT '15-Jan-2025' AS date_string FROM DUAL UNION ALL
  SELECT '30-Feb-2025' AS date_string FROM DUAL UNION ALL
  SELECT 'Not a date' AS date_string FROM DUAL
)
SELECT 
  date_string,
  VALIDATE_CONVERSION(
    date_string AS DATE, 
    'DD-Mon-YYYY',
    'NLS_DATE_LANGUAGE = American'
  ) AS "Is_Valid_Date"
FROM event_dates;

Result: (The function returns 1 only for the string that is a real, valid date.)

DATE_STRING   Is_Valid_Date
------------- -------------
15-Jan-2025               1
30-Feb-2025               0
Not a date                0