Running MySQL queries inside a loop - php

Question

I want to run multiple mysql queries in a loop. Maybe this the wrong approach but thats why I'm asking.
Example:
A user submits a array of userinput and i want loop through it an perform multiple mysql queries. If I hardcode the ID it works but if I set the ID as a VAR it dosen't. When using a VAR it alway shows a result with the last entry.
Best, Tim
if(isset($_POST['list'])){
$list=$_POST['list'];
$list_arr=explode(PHP_EOL, $list);
$list_arr_len=count($list_arr);
for ($i=0; $i < $list_arr_len; $i++) {
echo $list_arr[$i]."<br>";
$result = mysqli_query($con,"SELECT col FROM table where id='$list_arr[$i]'");
$row=mysqli_fetch_array($result,MYSQLI_NUM);
echo $row[0]."<br>";
}
mysqli_close($con);
}

Answer 1

You can do it in one query like this:
if(!empty($_POST['list'])){
$list=$_POST['list'];
$list_arr=explode(PHP_EOL, $list);
$list_id=implode("', '", array_map('mysqli_real_escape_string', $list_arr));
$result = mysqli_query($con,"SELECT col FROM table where id IN ('{$list_id}')");
while($row=mysqli_fetch_array($result,MYSQLI_NUM)) {
echo $row[0]."<br>";
}
mysqli_close($con);
}
in this example no matter which type of colum for id u use

Answer 2

Create PDO object and set it in exception mode
$dsn = 'mysql:dbname=testdb;host=127.0.0.1';
$user = 'dbuser';
$password = 'dbpass';
try
{
$pdo = new PDO($dsn, $user, $password);
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
catch (PDOException $e)
{
echo 'Connection failed: ' . $e->getMessage();
}
You are posting a comma separated list (I'd post an array but what the hell), so we're going to simply parse the string into integers and stick it in MySQL's IN clause
if(isset($_POST['list']))
{
$list = str_replace(["\r", "\n"], "", $_POST['list']);
$numbers = strpos($list, ',') !== false ? explode(",", $list) : (int)$list;
// This can probably bet written nicer, the idea is to have each number explicitly typecast to int so it's safe to stick in a query directly
// Basically, you want "1,2,3,4,5" without the possibility of having some bad input here
if(is_array($numbers))
{
$numbers = implode(",", array_map(function($number)
{
return (int)$number;
}, $numbers));
}
// And the nice, one liner, where you query and fetch the records which are now in the array called $records
$records = $pdo->query(sprintf("SELECT * FROM your_table WHERE id IN(%s)", $numbers))->fetchAll(PDO::FETCH_ASSOC);
}
Note: I didn't test the code so don't copy paste it, it most likely contains errors. I wrote the answer to show how easy it is to use PDO and retrieve results easily, in one liner.

Answer 3

I think this shall work:
$result = mysqli_query($con,"SELECT col FROM table where id=".mysqli_real_escape_string($list_arr[$i])."");

Answer 4

First Create a string of all the ids and use IN(String of Ids) in your query and store all the data corresponding to id in an array.
$stringIds = "";
for ($i=0; $i < $list_arr_len; $i++)
{
if (is_null($stringIds))
{
$stringIds = '"' . $list_arr[$i] . '"';
}
else
{
$stringIds .= ',"' . $list_arr[$i] . '"';
}
}
$resulSet = mysqli_query($con, ""SELECT col FROM table where id='?'"");
while($row = mysqli_fetch_assoc($resulSet))
{
mainArray[$row['id']] = $row;
}
Now, your able to fetch all your data from the array using foreach loop and please use PDO to avoid SQL Injection.

Answer 5

Problem was:
\n \r
This c0de works for me now ( also IN('') might be the better idea ):
if(isset($_POST['list'])){
$list=$_POST['list'];
//echo $list;
$replace = array("\n", "\r");
$id = str_replace( $replace, ",", $list);
$id_arr = explode(",", $id);
$id_arr_len = count($id_arr);
for ($i=0; $i < $id_arr_len; $i++) {
# code...
$result = mysqli_query($con,"SELECT col1,col2 FROM table where id='$id_arr[$i]'");
while($row = mysqli_fetch_assoc($result)){
echo $row['col1'].': ';
echo $row['col2'].'<br/>';
}
}
}