MAX and COUNT sql query - php

Question

I need to know how to use MAX() and COUNT() query to display the "fiser" table entries that contain the primary "codp" key that comes from the "products" table, depending on a previously selected period?
Table products : codp, denp ;
Table orders: codc,codp ;
Table returns : codr, datar, codc, codp
<?php
if(isset($_POST['add'])){
$sql = "SELECT p.denp, a.datar,MAX(p.codp)
FROM ( SELECT COUNT(p.codp) FROM products p ) products p
INNER JOIN orders o ON p.codp=o.codp
INNER JOIN returns r ON o.codc=r.codc
WHERE r.datar>=STR_TO_DATE('".$_POST['d1']."','%Y-%m-%d')
AND r.datar<=STR_TO_DATE('".$_POST['d2']."','%Y-%m-%d') ";
$result = mysqli_query($conn, $sql);
$queryResult = mysqli_num_rows($result);
if($queryResult > 0 ){
while ($row = mysqli_fetch_assoc($result)) {
echo "
<table border=1 >
<tr>
<td><p> ".$row['codp']." </p></td>
<td><p> ".$row['denp']." </p></td>
<td><p> " .$row['codr']." </p></td>
<td><p> " .$row['datar']." </p></td>
<td><p> " .$row['codc']." </p></td>
</tr> </table> ";
}
} else {
echo " No results!" ;
}
}
?>

Answer 1

You should use group by for codp and the join the related result eg:
$sql = "SELECT p.denp, r.datar,MAX(p.cnt_codp)
FROM (
SELECT codp, COUNT(*) as cnt_codp FROM products
group by codp
) products p
INNER JOIN orders o ON p.codp=o.codp
INNER JOIN returns r ON o.codc=r.codc
WHERE r.datar>=STR_TO_DATE('".$_POST['d1']."','%Y-%m-%d')
AND r.datar<=STR_TO_DATE('".$_POST['d2']."','%Y-%m-%d')
GROUP BY p.denp, r.datar ";
and you should check for your db driver for param bindig instead of use of php var in sql (you are at risk for sql injection)
and you should also use a group by for not aggreated column or reeval the question if you need the values related to max result (the use of aggregation function without a proper group by columns for not aggreagated is depreacted in sql ai the most recent version of mysql is not allowed)