PHP SQL, Query Returns Only One Row of Data

SQL Query Returning Only one row in result

This might have something to do with it: you are re-writing your $result variable in the loop.

$result = mysqli_query($conn,"SELECT user_image FROM 'users' WHERE id=$user_id");

Why PHP function is returning Only the one row from mysql

The return should be outside the while loop !

Here is how you can get all the rows :

     function getAll()
     {
        global $con;

        $SQL  = "SELECT * FROM users";

        $stmt = $con->query($SQL);

        if($stmt->num_rows > 0){

            $arr = array();

            while($row = $stmt->fetch_row())
            {
                $arr[] = $row;
            }
            return $arr;
        }
     }

Or you can do something like this return a generator and loop through :

function getAll()
     {
        global $con;

        $SQL  = "SELECT * FROM users";

        $stmt = $con->query($SQL);

        if($stmt->num_rows > 0){

            while($row = $stmt->fetch_row())
            {
                yield $row;
            }
        }
     }

see the result here !

echo '<pre>';

foreach (getAll() as $value) {
 print_r($value);
}

query returns only one row when using PHP

mysqli_fetch_assoc returns an associative result of one row. See here

You need to do something like this:

while ($row = $result->fetch_assoc()) {
    $data[] = $row;
}

that will give you an array of associative arrays of query results.

Query only returning one row (PHP / MYSQL)

The problem is that you have html code inside the loop section, meaning you're creating a map for each coordinate. I think the best approach, considering your code, is to create an array of markers and then converting it to JSON using the json_encode method and printing it to a variable on your javascript code.

// Display the results of the query
$markers = [];

while($row = $result->fetch_assoc()) {
    $markers[] = [
        'coords' => [ 
            'lat' => $row['lat'],
            'lng' => $row['lng']
        ],
        'iconImage' => 'images/hs.png',
        'content' => "<h2>Hydrant - Number {$row['id']}</h2><b>Flow</b> {$row['flow']} Liters per minute<br><b>Pressure</b> {$row['pressure']} bar<br><br>{$row['type']}<br>{$row['lid']}<br><br><center><a href=images/hydrants/{$row['id']}.jpg><img src=images/hydrants/{$row['id']}.jpg width=100%></a>Updated {$row['updated']}<br><br><a href=\"report.php?id={$row['id']}\">Report problem with this hydrant</a></center>"
    ];
}

Then on your javascript, simply add a variable like this and print the encoded result:

var markers = <?php echo json_encode($markers); ?>;

The whole code:

<?php include("header.php");

// Connect to the hydrants table and set ORDER BY to ASC or DESC

$sql = "SELECT id, lat, lng, flow, pressure, type, lid, updated FROM hydrants_OLD ORDER BY id ASC";
$result = $conn->query($sql);

// Display the results of the query
$markers = [];

while($row = $result->fetch_assoc()) {
    $markers[] = [
        'coords' => [ 
            'lat' => $row['lat'],
            'lng' => $row['lng']
        ],
        'iconImage' => 'images/hs.png',
        'content' => "<h2>Hydrant - Number {$row['id']}</h2><b>Flow</b> {$row['flow']} Liters per minute<br><b>Pressure</b> {$row['pressure']} bar<br><br>{$row['type']}<br>{$row['lid']}<br><br><center><a href=images/hydrants/{$row['id']}.jpg><img src=images/hydrants/{$row['id']}.jpg width=100%></a>Updated {$row['updated']}<br><br><a href=\"report.php?id={$row['id']}\">Report problem with this hydrant</a></center>"
    ];

    // echo "{$row['id']}, {$row['lat']}, {$row['lng']}, {$row['flow']}, {$row['pressure']}, {$row['type']}, {$row['lid']}, {$row['updated']}, <br>" ;
}

?>
    <head>
      <title>Hydrants</title>

      <meta name="viewport" content="initial-scale=1.0">
          <link rel="Shortcut Icon" href=images/hl.png>
       <meta name="mobile-web-app-capable" content="yes">
       <link rel="icon" href="images/hl.png">
      <!--<meta name="apple-mobile-web-app-capable" content="yes">-->
      <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
      <meta name="apple-mobile-web-app-title" content="Hydrants">

      <link rel="apple-touch-icon" href="images/h-apple.png"><link rel="apple-touch-startup-image" media="(device-width: 320px) and (device-height: 568px) and (-webkit-device-pixel-ratio: 2)" href="images/h-apple.png"><link rel="apple-touch-startup-image" media="(device-width: 768px) and (orientation: portrait)" href="images/h-apple.png">
      <meta charset="utf-8">
      <style>
        /* Always set the map height explicitly to define the size of the div
         * element that contains the map. */
        #map {
          height: 100%;
        }
        /* Optional: Makes the sample page fill the window. */
        html, body {
          height: 100%;
          margin: 0;
          padding: 0;
        }
      </style>
  </head>
  <body bgcolor="#ffffff">      
    <div id="map"></div>

    <script>

        var map, infoWindow;
        function initMap(){
        // Map options
        var options = {
          // zoom:17,
          zoom:14,
          center: {lat: 53.428345, lng: -6.244447},
        }

        var markers = <?php echo json_encode($markers); ?>;

        var map = new google.maps.Map(document.getElementById('map'), options);

        // Loop through markers
        for(var i = 0;i < markers.length;i++){
          // Add marker
          addMarker(markers[i]);
        }

        // Add Marker Function
        function addMarker(props){
          var marker = new google.maps.Marker({
            position:props.coords,
            map:map,
            //icon:props.iconImage
          });

          // Check for customicon
          if(props.iconImage){
            // Set icon image
            marker.setIcon(props.iconImage);
          }

          // Check content
          if(props.content){
            var infoWindow = new google.maps.InfoWindow({
              content:props.content
            });
                 marker.addListener('click', function(){
              infoWindow.open(map, marker);
            });
          }
        }

          infoWindow = new google.maps.InfoWindow;

        }

      </script>
      <script async defer
      src="https://maps.googleapis.com/maps/api/js?key=0000MYAPIKEY0000&callback=initMap">
      </script>
    </body>

<?php
// Close database connection
$conn->close();

?>

MySQL returns only one row

$query = mysql_query("SELECT `title`,
                             `url_title`
                        FROM `fastsearch`
                       WHERE `tags`
                            LIKE '%$q%'
                       LIMIT 5");

while ($row = mysql_fetch_assoc($query)) {
    print_r($row);
}

You misspelled $query in your example
mysql_fetch_assoc() will return a row each time it is called, and FALSE when out of rows. Use that to your advantage, by assigning a variable to it in the condition. Within the while() loop, $row will be the current row.

Sql query returns only first row

You need to use fetchALL() as fetch() only returns one row according to the docs:

Fetches a row from a result set associated with a PDOStatement object.

$query = "SELECT Email from client";
$result = $db->query($query)->fetchALL();
foreach($result as $email){
    echo $email["Email"]."\n";
}