How to Handle Duplicate Entries in MySQL and Provide Custom Error Messages?

Handling Duplicate Entries in MySQL

When encountering duplicate entries in a MySQL database, the standard error message can be uninformative for users. To improve the user experience, it's necessary to handle this error and provide a customized message.

Checking for Duplicate Keys

To check for a specific MySQL error, such as duplicate keys, we need to retrieve the error code. In the case of duplicate keys, the error code is 1062.

Using Error Codes in PHP

PHP provides the mysqli_errno() function to retrieve the error code from a MySQL query. We can use this function to compare the error code with the known error code for duplicate keys (1062):

mysqli_query('INSERT INTO ...');
if (mysqli_errno() == 1062) {
    echo 'Duplicate entry. Please enter a different value.';
}

Programming Style Note

While using magic numbers like 1062 is convenient, it's recommended to assign known error codes to named constants. This improves code readability and makes it easier to maintain in the long run, as the meaning of the constant is more explicit than the numeric value.

For example, you could define the following constant:

define('MYSQLI_CODE_DUPLICATE_KEY', 1062);

And use it in your code:

if (mysqli_errno() == MYSQLI_CODE_DUPLICATE_KEY) {
    // ...
}

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