php foreach loop SQL table name query - php

Question

I have this php code to do a query foreach loop going through the table name in variable $rowA but I got an "Array to string conversion" error. Does anyone know why? Can we do a query loop this way?
$sql = "SELECT `id`, `first_name` FROM `clients` ORDER BY `id` DESC";
$result = $DB_CON_C->query($sql);
$sql_email = "SELECT `email` FROM `clients` ORDER BY `id` DESC";
$account = $DB_CON_C->query($sql_email);
foreach($result as $row) {
foreach($account as $rowA) {
$stmt = "SELECT SUM(value) AS total_amount FROM `".$rowA."`";
$amount = $DB_CON_C->query($stmt);
$sum = $amount->total_amount;
$data_row .= '<tr>'
. '<td>' .$row['id'].'</td>'
. '<td>' .$row['first_name'].'</td>'
. '<td>' .$sum.'</td>';
}
}
}
$data_row .= '</tbody>'
. '</table>';
echo $data_row;

Answer 1

There seems to be a fundamentally odd issue with the way you are handling your data values.
Take your first query, $result, this will (obviously depending on the exact $DB_CON_C class method) output an array of values for id and first_name
Yet on the second call, $account using the same method you are then calling the values as if they're class variables $amount->total_amount.
I would suspect that one of these syntax is wrong, but without seeing your class I can't say which.
Do you realise that your two SQL calls are both returning the whole database?
Do you realise that you're using the data value (email address) in one table as the column name in another table? This can work, but this really isn't best practise.
You do not need to use the concaenator . for strings over new lines.
$string = "Hello
this string works fine";
as white space is reduced to one character length in HTML so it doesn't matter (much).
Solving your issue:
var_dump($account) once the value has been populated, same with $results, do var_dump($results) and see what is in the value, if these are class variables or arrays of data?
Seeing that both your variables are calling different parts of the same table, I have rewritten your code below:
$sql = "SELECT `id`, `first_name`, `email` FROM `clients` ORDER BY `id` DESC";
$result = $DB_CON_C->query($sql);
/***
* $result is assumed to be an array, within which is a set of values such as:
* $result[0]['id']
* $result[0]['first_name']
* $result[0]['email']
* $result[1]['id'], etc.
***/
foreach($result as $row) {
$stmt = "SELECT SUM(value) AS total_amount FROM `".$row['email']."`";
$amount = $DB_CON_C->query($stmt);
/***
* this is inconsistent, your data structure must be like $result as it
* uses the same methods, therefore you will need to enter the first
* "row" before getting the 'total_amount' value
***/
$sum = $amount[0]['total_amount'];
$data_row .= '<tr>
<td>' .$row['id'].'</td>
<td>' .$row['first_name'].'</td>
<td>' .$sum.'</td>
</tr>'; //you forgot your /tr !!
}
// Always clean up after foreach loops.
unset($row);
$data_row .= '</tbody>
</table>';
echo $data_row;

Answer 2

You're trying to parse a database row to a string, even though it contains only one thing.
Change the following line
$stmt = "SELECT SUM(value) AS total_amount "
. "FROM `".$rowA."`";
to
$stmt = "SELECT SUM(value) AS total_amount "
. "FROM `".$rowA['email']."`";
$rowA is a database row and contains the email field from the database.