SQL/PHP Conditional SELECT and UPDATE - php

Question

I'm trying to return 5 unused values from the codes column of the table below and then set used in the related row to 1.
|--- codes ---| | used |
| FIomQVu71l | | 0 |
| 4TW0lwLWNK | | 0 |
| SjzLB2Shzr | | 0 |
| uTWJrtCgh4 | | 0 |
| tLwOwYGz5R | | 0 |
| byEhzYMWJG | | 0 |
| XFBmGzDGIR | | 0 |
I've managed to get the code working to output 5 random values from codes where used = 0
<?php
$sql = "SELECT codes FROM code_table WHERE used =0 ORDER BY rand() LIMIT 5";
$records = mysql_query($sql, $connection);
while($rows = mysql_fetch_array($records)){
echo "Code: " . $rows['codes'] . "<br />";
?>
But now I'm lost as to how to update the used value for each output codes. All of my attempts have updated every single instance of used to 1 rather than just the instances associated with the 5 codes

Answer 1

You could store the rows in a temporary table. Note that this is not entirely concurrency safe. If another query comes between the insert and the update, it might grab the same rows.
CREATE TEMPORARY TABLE IF NOT EXISTS tmp_codes (codes varchar(50));
-- Get five new rows
INSERT INTO tmp_codes
(codes)
SELECT codes
FROM code_table
WHERE used = 0
ORDER BY
rand()
LIMIT 5;
-- Update the five rows
UPDATE code_table
SET used = 1
WHERE codes in
(
SELECT codes
FROM tmp_codes
);
-- Return to application
SELECT codes
FROM tmp_codes;
DROP TABLE tmp_codes;
Example at SQL Fiddle.

Answer 2

You should execute an update query:
$sql = "SELECT codes FROM code_table WHERE used =0 ORDER BY rand() LIMIT 5";
$records = mysql_query($sql, $connection);
$codes = array();
while($rows = mysql_fetch_array($records)){
echo "Code: " . $rows['codes'] . "<br />";
$codes[] = "'" . $rows['codes'] . "'";
}
$updateSql = "UPDATE code_table SET used = 1 WHERE codes in(" . implode (',' , $codes ) . ")";
$res = mysql_query($updateSql, $connection);