Check if exists, if so, update by 1++, if not insert - php

Question

Hey guys quick question, I currently have an insert statement
$query= "INSERT into new_mail VALUES ('$to1', '0')"; where fields are username, and message_number
Currently what I would do to check if the entry exists, is do a select query then check the number of rows with mysql_num_rows (php). If rows==1 then I get the current message_number and set it equal to
$row['message_number']+1.
Then I update that entry with another query.
Is there an easier way to do all this in just mysql with just one query (check if exists, if not insert, if so update message_number, increase by 1)?

Answer 1

Depending on how your table is structured, you may be able to use the ON DUPLICATE KEY UPDATE (link to the MySQL manual) feature of INSERT:
INSERT into new_mail VALUES ('$to1', '0') ON DUPLICATE KEY UPDATE message_number=message_number+1

Answer 2

Use INSERT...ON DUPLICATE KEY UPDATE. The MySQL manual has an example which does almost exactly what you need:
INSERT INTO table (a,b,c) VALUES (1,2,3)
ON DUPLICATE KEY UPDATE c=c+1;
To make this work you need to add a UNIQUE index on the column that you use to check for duplicates. There is one important warning though:
In general, you should try to avoid using an ON DUPLICATE KEY clause on tables with multiple unique indexes.

Answer 3

Got a little confused by your question and your table structures but I think you want something like this.
INSERT INTO new_mail (username, message_number)
VALUES ($username, $message_number)
ON DUPLICATE KEY UPDATE message_number=message_number + 1;
This is presuming username is your primary key (more likely something like userid). Hope this helps.

Answer 4

EDIT: The ON DUPLICATE KEY UPDATE answers are better, but you could do this (eludes the select query):
Assuming you're using the mysqli extenson:
$db = //Some construction of mysqli object;
$sql = 'UPDATE tablename SET RowValue = RowValue + 1 WHERE message_number = ?';
$updateStatement = $db->prepare($sql);
$updateStatement->bind_param('i', $message_number);
$message_number = //Set message number;
$updateStatement->execute();
if ($updateStatement->affectedRows == 0) {
$sql = 'INSERT INTO tablename (RowValue, message_number) VALUES (?, ?)';
$insertStatement = $db->prepare($sql);
$insertStatement->bind_param('ii', $rowValue, $messageNumber);
$rowValue = something;
$messageNumber = something;
$insertStatement->execute();
}