I am getting this error, who can help mw with that?

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I ma getthing this:Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, bool given in C:\xampp\htdocs\donatetheblood\donate.php on line 221

What I have tried:

<pre> if(isset($_POST['email']) && !empty($_POST['email'])){
    
		$pattern= '/^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$/';
		
	
	  if(preg_match($pattern, $_POST['email'])){
		
		$check_email= $_POST['email'];
		$sql="SELECT eamil FROM donar WHERE email='$check_email'";
	
		$result= mysqli_query($connection, $sql);
	
		if(mysqli_num_rows($result)>0){
	
		$emailError= '<div class="alert alert-danger alert-dismissible fade show" role="alert">
		Sorry!! this email address is already exist.
		<button type="button" class="close" data-dismiss="alert" aria-label="Close">
		  <span aria-hidden="true">×</span>
		</button>
	   </div>';
	
	
	
		}else{
	
			$email= $_POST['email'];
	
		}

Posted 16-Jul-21 19:38pm

Alirimon

Updated 16-Jul-21 19:53pm

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OriginalGriff · Answer 1 · 2021-07-16T19:53:00

Read the documentation: PHP mysqli query() Function[^]
It says:

Quote:
Return Value: For successful SELECT, SHOW, DESCRIBE, or EXPLAIN queries it will return a mysqli_result object. For other successful queries it will return TRUE. FALSE on failure

So ... since the error describes a bool value as a parameter instead of a result set, the SELECT query is failing, either because of the connection or part of the query itself.

One possible reason for this is that you are doing something very, very dangerous: Never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Always use Parameterized queries instead.

When you concatenate strings, you cause problems because SQL receives commands like:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood'

The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;--'

Which SQL sees as three separate commands:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'x';

A perfectly valid SELECT

SQL

DROP TABLE MyTable;

A perfectly valid "delete the table" command

SQL

--'

And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.

So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?