Question

I am getting an error when querying a table in my MySQL database. It’s the standard one with mysqli_num_rows when there is no value in the variable that’s being passed:

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in folder/file.php on line 29

Problem is I can’t find the syntax error. I’ve looked at it a ton of times. Here’s what my code is:

$sql_messages = "SELECT * FROM messages WHERE to='$userid'";
$result_messages = $mysqli->query($sql_messages);
$num_rows_messages = mysqli_num_rows($result_messages);

I tried a fetch array but that gave me the similar error. Nothing is getting passed into $result_messages I suppose. I echo’ed out $userid and that has a value and I’ve checked my database and there is a table ‘messages’ with a field ‘to’. I’m connected to the right database because I have this code before this query:

$sql="SELECT * FROM users WHERE firstname='$firstname' && lastname='$lastname'";
$result = $mysqli->query($sql);
$row = mysqli_fetch_array($result);

And that works fine. It is the third query on the page, is there some sort of limit? Does anyone see a syntax error that I’m overlooking? Thanks, sorry if it’s a small little error!

Answer 1

It’s because $mysqli->query() returned boolean FALSE, which, according to the mysqli::query() docs, it does when an error happens. You can get more detail on the error by accessing $mysqli->errno and $mysqli->error.

I’m guessing that the root of the problem lies in the query which references a column called to, which is a MySQL reserved word. Try surrounding the word to in your query with backticks. Like this:

$sql_messages = "SELECT * FROM messages WHERE `to`='$userid'";

Really, though you should avoid naming columns and tables reserved words. Consider renaming the column if feasible.