Displaying results in a search table (PHP) - php

Question

This has probably been asked before, please feel free to link me or whatever, I just couldn't find exactly what I'm after.
It's pretty simple, I need to display the results of a search form. That part is easy and I can get that to work. What I'm having trouble with is when no results match what the user searched.
I'm fairly certain I need to just use an IF statement but I'm not very experienced with PHP and cannot figure out how to correctly display the code.
This is what I have so far:
$query = "SELECT * FROM search WHERE isbn='$isbn' OR bookname='$bookname' OR author='$author' OR category='$category'";
if (!$query)
{
echo "No results found in the database. Please go back and search again.";
}
My question is: How do I get the 'No results found...' message to display when the users search doesn't match anything in the database?
NOTE - I get very confused very quickly when it comes to trying to understand certain terms within PHP and SQL so please try to explain your answer like you would to an absolute beginner.
Many thanks in advance.

Answer 1

You want to show the "No results found"-message when no rows are found in the database table.
To do this, you can use below PHP and SQL code:
$sql = "SELECT * FROM search WHERE isbn='$isbn' OR bookname='$bookname' OR author='$author' OR category='$category'";
$query = $db->prepare($sql);
$query->execute();
$rows = $query->fetch(PDO::FETCH_NUM);
if($rows[0]) {
// Row exists
} else {
echo "No results found in the database. Please go back and search again.";
}
Note that the above answer is vulnerable to SQL injection attacks.
To prevent SQL injection attacks, it is recommended that you prepare and bind all user-submitted data, here is a better example that shows how SQL injection attacks can be prevented: (full example, including database connection)
$db = new PDO($dsn);
$db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
$db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$query = $db->prepare("SELECT * FROM search WHERE isbn=:isbn OR bookname=:bookname OR author=:author OR category=:category");
$query->execute([ ':isbn'=>$isbn, ':bookname'=>$bookname, ':author'=>$author, ':category'=>$category ]);
$rows = $query->fetch(PDO::FETCH_NUM);
if($rows[0]) {
// Row exists
} else {
echo "No results found in the database. Please go back and search again.";
}

Answer 2

Assuming you are using Mysqli ,
//connect with mysql
$conn = mysqli_connect("localhost", "user", "password", "db");
//here is the query
if($result = mysqli_query($conn,"SELECT * FROM search WHERE isbn='$isbn' OR bookname='$bookname' OR author='$author' OR category='$category'")){
if(mysqli_num_rows($result) > 0){
//mysqli_num_rows() returns the number of rows in a result .
//when it is greater than zero, it has some results
}
else{
echo "No results found in the database. Please go back and search again.";
//Do something if no results returned
}
}
//finally free the results
mysqli_free_result($result);
mysqli_close($conn);