MySQL への挿入時に文字列と主キー ID を連結するにはどうすればよいですか?

Concatenating a String and Primary Key ID during Insertion

Inserting data into a MySQL table can be straightforward, as demonstrated in the provided code. However, if you wish to create usernames as 'user' concatenated with an auto-incremental primary key ID (user1, user2, user3, etc.), a direct approach requires some consideration.

Concatenation limitations:

• AUTO_INCREMENT limitations: The primary key is not generated until after the insert operation, so a trigger approach cannot assign the concatenated value during the initial insert.

Alternative approach:

To address this limitation, you can perform the following steps:

1. Insert the data: Execute the INSERT statement as provided.
2. Retrieve the inserted ID: Use the mysqli_insert_id() function to retrieve the auto-generated ID.
3. Update the username: Execute an UPDATE statement to concatenate the 'user' string with the retrieved ID:

$query = 'UPDATE `users` SET `username` = CONCAT("user", ?) WHERE `id` = ?';
$stmt = $mysqli->prepare($query);
$stmt->bind_param("ii", $id, $id);
$stmt->execute();

Considerations for non-AUTO_INCREMENT IDs:

If the user_id is not an AUTO_INCREMENT value, you can directly concatenate the 'user' string and the specified ID in your PHP code before passing it as a parameter in the insert statement.

Additional notes:

• Using MySQL 5.7 generated columns is not an option in this case, as it results in an error due to the auto-increment nature of the primary key.
• This two-step approach ensures that the username is correctly updated after the initial insert.

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