Retaining Older Uploaded Image In Db - php

Question

I have a page in my clients dashboard for editing his about content.
Once i click on edit button it redirects to another page and there is an option for uploading new image and also content.
Problem :If no new image is uploaded suppose only some text fields are changed and clicked on update the text content changes and redirects to main page but image is deleted from db,but i don't want image to be deleted from the db if no new picture is uploaded.
Two Files Are there
1)index.php
2)editabout.php
index.php
<div class="main-container">
<div class="row">
<div class="container">
<div class="col-lg-12">
<div class="row">
<?php include('db.php'); $select=mysql_query("SELECT * FROM `about`"); while($row=mysql_fetch_array($select)){?>
<div class="col-md-3"><img id="profileimage" src="about/<?php echo $row['image']; ?>" style="width:100%;height:200px;" class="img-thumbnail img-responsive" required>
<div class="row">
<div class="col-md-6"> <input style="width:100%;" class="btn btn-info btn-lg mb-3 mr-3" type="submit" value="Edit"></div>
</div>
</div>
<?php}?>
</div>
</div>
</div>
</div>
editabout.php
<div class="row">
<div class="col-lg-4">
<form action="" method="post" enctype="multipart/form-data">
<div class="main-container file-upload">
<div class="file-upload__dropzone">
<?php
include('db.php');
$select=mysql_query("SELECT * FROM `about` where `sl.no`='$bid' ");
while($row=mysql_fetch_array($select)){
?>
<img id="profileimage" src="about/<?php echo $row['image']; ?>" value="<?php echo $row['image']; ?>" class="img-thumbnail img-responsive" style="width:100%;height:200px;">
<?php } ?>
<div class="file-upload__browse-files">
<button class="btn btn-outline-info btn-lg btn-block btn-rounded file-upload__browse-btn">Browse files</button>
<input id="upload-files-default" name="img" type="file" multiple class="upload" onchange="readURL(this);">
</div><br>
<button class="btn btn-success btn-lg mb-2 mr-3" name="ok" type="submit">Update</button>
</div>
</div>
</form>
</div>
Php code for uploading
include('db.php');
if(isset($_POST['ok']))
{
$photo=$_FILES['img']['name'];
$target_dir = "about/";
$location = $target_dir .$_FILES["img"]["name"];
move_uploaded_file($_FILES['img']['tmp_name'],$location);
$query1="UPDATE `about` SET `image`='$photo',
`up_date`=now()
WHERE `about`.`sl.no` ='$bid'";
mysql_query($query1);

Answer 1

You have to check does the file exist/uploaded or not before executing any query. As an example below:
if(is_uploaded_file($_FILES["img"]["tmp_name"] && file_exists($_FILES["img"]["tmp_name"])){
//update query with picture
//move_uploaded_file here
}else{
//Only query updating does details without move_uploaded_file
}
Above code must be put in the if(isset($_POST["ok"])) code block.