Fixing the Oracle Error: Ora-01810 - A Guide to Resolving the Double Format Code Issue

In this guide, we will cover the steps to resolve the Oracle error ORA-01810: format code appears twice that occurs when there is a duplication of format code in the TO_DATE or TO_CHAR functions in Oracle SQL. We will also provide answers to frequently asked questions about this error.

Table of Contents

• Understanding the Oracle Error Ora-01810
• How to Resolve the Ora-01810 Error
• Frequently Asked Questions (FAQs)

Understanding the Oracle Error Ora-01810

The Oracle error ORA-01810: format code appears twice is encountered when the TO_DATE or TO_CHAR functions are called with a format string that has a duplicate format code. The TO_DATE function is used to convert a string to a date, while the TO_CHAR function is used to convert a date to a string. Both functions have a format string as a parameter that defines the expected format of the input string or output string.

For example, the following SQL code will result in the ORA-01810 error:

SELECT TO_DATE('2021-08-01', 'YYYY-MM-DD-DD') FROM DUAL;

In this case, the format string YYYY-MM-DD-DD has the DD format code twice, resulting in the error.

How to Resolve the Ora-01810 Error

To resolve the ORA-01810 error, you need to identify the duplicate format code in the format string and remove it or replace it with the correct format code. Here is a step-by-step guide on how to resolve the error:

Identify the SQL statement causing the error. Look for the TO_DATE or TO_CHAR functions in the statement.

Examine the format string parameter in the function call. Identify any duplicate format codes.

Remove the duplicate format code or replace it with the correct format code. For example, if the format string is YYYY-MM-DD-DD, you should remove the second DD code:

SELECT TO_DATE('2021-08-01', 'YYYY-MM-DD') FROM DUAL;

1. Re-run the SQL statement to ensure that the error is resolved.

You can find more information on format codes in the Oracle official documentation.

Frequently Asked Questions (FAQs)

What are the format codes in Oracle SQL?

Format codes are placeholders used in the TO_DATE and TO_CHAR functions in Oracle SQL to define the expected format of the input string or output string. Some common format codes include:

• YYYY: 4-digit year
• MM: 2-digit month
• DD: 2-digit day
• HH24: 2-digit hour (00-23)
• MI: 2-digit minute
• SS: 2-digit second

A complete list of format codes can be found in the Oracle documentation.

How do I use the TO_DATE function in Oracle SQL?

The TO_DATE function is used to convert a string to a date in Oracle SQL. Its syntax is:

TO_DATE(string, format_string[, nls_language])

• string: The string to be converted to a date
• format_string: The format of the input string, defined using format codes
• nls_language: (Optional) The language to be used for month and day names

For example:

SELECT TO_DATE('2021-08-01', 'YYYY-MM-DD') FROM DUAL;

This code will convert the string '2021-08-01' to a date with the format 'YYYY-MM-DD'.

How do I use the TO_CHAR function in Oracle SQL?

The TO_CHAR function is used to convert a date to a string in Oracle SQL. Its syntax is:

TO_CHAR(date, format_string[, nls_language])

• date: The date to be converted to a string
• format_string: The format of the output string, defined using format codes
• nls_language: (Optional) The language to be used for month and day names

For example:

SELECT TO_CHAR(SYSDATE, 'YYYY-MM-DD') FROM DUAL;

This code will convert the current system date to a string with the format 'YYYY-MM-DD'.

Can I use multiple format codes in a single format string?

Yes, you can use multiple format codes in a single format string to define the expected format of the input or output string. For example:

SELECT TO_CHAR(SYSDATE, 'YYYY-MM-DD HH24:MI:SS') FROM DUAL;

This code will convert the current system date and time to a string with the format 'YYYY-MM-DD HH24:MI:SS'.

How can I prevent the Ora-01810 error in the future?

To prevent the ORA-01810 error in the future, always ensure that you double-check the format string in the TO_DATE or TO_CHAR functions to avoid any duplicate format codes. It is also helpful to review the Oracle documentation to familiarize yourself with the correct format codes and their usage.