Single Result from Database by using mySQLi

Question 1

I am trying to use mySQLi for the first time. I have done it in case of loop. Loop results are showing but i am stuck when i try to show single record. Here is loop code that is working.

<?php
// Connect To DB
$hostname="localhost";
$database="mydbname";
$username="root";
$password="";

@$conn = mysqli_connect($hostname, $username, $password)
        or die("Could not connect to server " . mysql_error()); 
    mysqli_select_db($conn, $database)
        or die("Error: Could not connect to the database: " . mysql_error());

    /*Check for Connection*/
    if(mysqli_connect_errno()){
        // Display Error message if fails
        echo 'Error, could not connect to the database please try again again.';
    exit();
    }
?>

<?php
$query = "SELECT ssfullname, ssemail FROM userss ORDER BY ssid";
$result = mysqli_query($conn, $query);
@$num_results = mysqli_num_rows($result);
?>

<?php
/*Loop through each row and display records */
for($i=0; $i<$num_results; $i++) {
$row = mysqli_fetch_assoc($result);
?>

<?php // echo 'Name' .$row['ssfullname'] . 'email' . $row['ssemail'] . "n"; ?>

Name: <?php print $row['ssfullname']; ?>
<br />
Email: <?php print $row['ssemail']; ?>
<br /><br />

<?php 
// end loop
} 
?>

Above code is fine in case of loop. Now how do i show single record, any record, name or email, from first row or whatever, just single record, how would i do that? In single record case, consider all above loop part removed and lets show any single record without loop.

Question 2

When just a single result is needed, then no loop should be used. Just fetch the row right away.

In case you need to fetch the entire row into associative array:
```
  $row = $result->fetch_assoc();
```

in case you need just a single value

  $row = $result->fetch_row();
  $value = $row[0] ?? false;

The last example will return the first column from the first returned row, or false if no row was returned. It can be also shortened to a single line,

$value = $result->fetch_row()[0] ?? false;

Below are complete examples for different use cases

Variables to be used in the query

When variables are to be used in the query, then a prepared statement must be used. For example, given we have a variable $id:

$query = "SELECT ssfullname, ssemail FROM userss WHERE ud=?";
$stmt = $conn->prepare($query);
$stmt->bind_param("s", $id);
$stmt->execute()
$result = $stmt->get_result();
$row = $result->fetch_assoc();

// in case you need just a single value
$query = "SELECT count(*) FROM userss WHERE id=?";
$stmt = $conn->prepare($query);
$stmt->bind_param("s", $id);
$stmt->execute()
$result = $stmt->get_result();
$value = $result->fetch_row()[0] ?? false;

The detailed explanation of the above process can be found in my article. As to why you must follow it is explained in this famous question

No variables in the query

In your case, where no variables to be used in the query, you can use the query() method:

$query = "SELECT ssfullname, ssemail FROM userss ORDER BY ssid";
$result = $conn->query($query);
// in case you need an array
$row = $result->fetch_assoc();
// OR in case you need just a single value
$value = $result->fetch_row()[0] ?? false;

By the way, although using raw API while learning is okay, consider using some database abstraction library or at least a helper function in the future:

// using a helper function
$sql = "SELECT email FROM users WHERE id=?";
$value = prepared_select($conn, $sql, [$id])->fetch_row[0] ?? false;

// using a database helper class
$email = $db->getCol("SELECT email FROM users WHERE id=?", [$id]);

As you can see, although a helper function can reduce the amount of code, a class' method could encapsulate all the repetitive code inside, making you to write only meaningful parts - the query, the input parameters and the desired result format (in the form of the method's name).

Question 3

Normally, I wouldn't advocate having database queries inside loops; it is inefficient and can cause excessive load on your database server.

That said, I don't see much alternative unless you can refactor your data model. What you have is a parent/child relationship within a single table ("superseded_sku" references a child record of the same table). This is bad for what you are trying to do as you never know beforehand if the child record has any children of it's own.

Assuming refactoring is not feasible, you want to run the query, check if there are matching records, update the query and repeat until there are no more records.

Try something like this...

// get initial result set (don't forget to escape your variables)
$query = "SELECT superseded_sku FROM mar15 WHERE sku = '" .
        mysqli_real_escape_string($mysqli, $ss1) . "'";
$result = mysqli_query($mysqli, $query);

// loop while we have results
while(mysqli_num_rows($result) > 0) {
    $row = mysqli_fetch_array($result);

    // double check the row is valid
    if (empty($row["superseded_sku"])) {
        break;
    }
    $ss1 = $row["superseded_sku"];

    // run the query again to check for further superseded skus
    $query = "SELECT superseded_sku FROM mar15 WHERE sku = '" .
        mysqli_real_escape_string($mysqli, $ss1) . "'";
    $result = mysqli_query($mysqli, $query);
}

I would seriously advise against using this approach as a long term measure, as it does not scale well at all. You will almost certainly encounter server resource issues or timeouts, especially if your product list continues growing. You will need to give some thought to refactoring the data if this is something you plan to use in the future.

Question 4

The reason your select doesn't get populated is because the mysqli_query doesn't get a connection supplied.

Change:

$db = mysqli_query($queryusers);

Into:

$db = mysqli_query($db, $queryusers);

Also add the name between (else you get a list with no text):

while ( $d=mysqli_fetch_assoc($db)) {
  echo "<option value='{".$d['Name']."}'>".$d['Name']."</option>";
}

Hope this helped you out!

Question 5

You need to define a array and store your data into array inside loop . Use MYSQLI_ASSOC no need for incremented value

$deviceToken=array();
while ($row = $output->fetch_array(MYSQLI_ASSOC)) {
    $deviceToken[] = $row['uid'];
}
print_r($deviceToken);
for($i=0;$i<=count($deviceToken);$i++){
echo $deviceToken[$i];
}

Question 6

Whatever is given in the SELECT statement to mysqli_query is going to return a mysql_result type if the query was successful. So if you have a SELECT statement such as:

SELECT sum(field) FROM table1

you still need to fetch the row with the result, and the value of the sum() function will be the only entry in the row array:

$res = mysqli_query($dbh,'SELECT sum(field) FROM table1');
$row = mysqli_fetch_row($res);
$sum = $row[0];

Single Result from Database by using mySQLi

Answers

Variables to be used in the query

No variables in the query

php,loops,mysqli