ORA-01820: Format Code Unknown in Oracle
Introduction
The "ORA-01820: Format Code Unknown in Oracle" is a common issue in Oracle databases that can disrupt your SQL queries and data operations. This error arises when Oracle encounters a format code that it does not recognize while parsing a date or number. Understanding and resolving this error is essential for smooth database management and accurate data processing.
Causes of ORA-01820
The ORA-01820 error generally occurs due to the following reasons:
- Invalid Format Codes: This error occurs when the format code used in functions like
TO_DATE, TO_NUMBER, or similar is not valid. For example, using a non-existent format code like 'Q' for quarter in date formatting might trigger this error.
- Mismatch Between Format and Literal: When the format specified does not match the literal provided. For example, providing a date literal with a time zone when the format code does not accommodate it.
- Incorrect Function Usage: Using formatting functions incorrectly, such as providing an incorrect format string to
TO_DATE or TO_NUMBER functions, can result in this error.
How to Fix ORA-01820
To resolve the ORA-01820 error, you need to ensure that your format codes match the literals being processed. Here are some steps to fix the error:
1. Verify Format Codes
Ensure that all format codes used in your SQL queries are valid. For instance, the format codes for dates and numbers must be according to Oracle's documentation. Here's an example of correcting format codes:
-- Incorrect SQL Statement
SELECT TO_DATE('2024-12-31', 'YYYY-Q-DD') FROM dual;
-- Error: ORA-01820: format code unknown
-- Correct SQL Statement
SELECT TO_DATE('2024-12-31', 'YYYY-MM-DD') FROM dual;
In this case, 'YYYY-Q-DD' is not a valid date format code, while 'YYYY-MM-DD' is correct.
2. Ensure Literal Matches Format
Check that the format string accurately reflects the literal value being provided. For example:
-- Incorrect SQL Statement
SELECT TO_DATE('31-Dec-2024 10:00 AM', 'DD-Mon-YYYY') FROM dual;
-- Error: ORA-01820: format code unknown
-- Correct SQL Statement
SELECT TO_DATE('31-Dec-2024 10:00 AM', 'DD-Mon-YYYY HH:MI AM') FROM dual;
Here, the incorrect format string 'DD-Mon-YYYY' does not account for the time portion, causing the error.
3. Review Function Usage
Ensure that you are using the correct function with appropriate format strings. Incorrect usage might lead to format code errors. For example:
-- Incorrect SQL Statement
SELECT TO_NUMBER('1234.56', '99999.9999') FROM dual;
-- Error: ORA-01820: format code unknown
-- Correct SQL Statement
SELECT TO_NUMBER('1234.56', '99999.99') FROM dual;
In this example, '99999.9999' is not a valid numeric format, while '99999.99' is appropriate.
Examples
Here are a few examples to illustrate how the ORA-01820 error can occur and how to resolve it:
Example 1: Invalid Date Format Code
-- Incorrect SQL Statement
SELECT TO_DATE('2024-08-31', 'YYYY-DD-MM') FROM dual;
-- Error: ORA-01820: format code unknown
-- Correct SQL Statement
SELECT TO_DATE('2024-08-31', 'YYYY-DD-MM') FROM dual;
In this case, the format code 'YYYY-DD-MM' is incorrect; 'YYYY-MM-DD' should be used.
Example 2: Numeric Format Issue
-- Incorrect SQL Statement
SELECT TO_NUMBER('1,234.56', '99999,99') FROM dual;
-- Error: ORA-01820: format code unknown
-- Correct SQL Statement
SELECT TO_NUMBER('1234.56', '99999.99') FROM dual;
Here, '99999,99' is not a valid numeric format for this example. '99999.99' is correct.
Conclusion
The " ORA-01820: Format Code Unknown " can be a challenging issue to diagnose and fix. By ensuring that format codes are valid, literals match the format, and functions are used correctly, you can resolve and prevent this error. Accurate formatting is crucial for successful SQL queries and data integrity in Oracle databases.