How to perform an inner join sql [closed] - php

Question

Closed. This question needs debugging details. It is not currently accepting answers.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 6 years ago.
Improve this question
Attempting to try and join my table called 'UserCaseMessages' with my other table called 'Comments' using this exact sql command in php:
$sql = "
SELECT UserCaseMessages.DefendantID, Comments.CommentID
FROM UserCaseMessages
INNER JOIN Comments
ON UserCaseMessages.DefendantID = Comments.SenderID
";
$result = $conn->query($sql);
if ($result->num_rows > 0) // ERROR GETS THROWN ON THIS LINE {
}
Here is the connection part to my database (which occurs prior to the query):
$servername = "localhost";
$username = "username";
$password = "password";
// Get the username from the post
$userUsername = $_POST['string'];
// Create connection
$conn = new mysqli($servername, $username, $password);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
I get the following error:
PHP Notice: Trying to get property of non-object
I cannot figure out what I am doing wrong here!! Everything is spelled correctly and a checked and checked for any syntax errors and I can't find any, however I am new to this particular method. Please help!

Answer 1

Since you haven't responded to my comments (some 20+ minutes prior to my submitting this), I am posting the following answer.
You didn't choose a database here:
$servername = "localhost";
$username = "username";
$password = "password";
$conn = new mysqli($servername, $username, $password);
so you need to add the database parameter:
$servername = "localhost";
$username = "username";
$password = "password";
$database = "your_DB";
$conn = new mysqli($servername, $username, $password, $database);
Read the manual on connecting with the MySQLi API:
http://php.net/manual/en/function.mysqli-connect.php
Check for errors on the query also:
http://php.net/manual/en/function.mysql-error.php
Plus, make sure the POST array does contain a value. Something in regards to the HTML form you didn't post.
The form's element must contain a matching name attribute:
name="string" and there must be a POST method for <form>.
method="post".
FYI: <form> is the equivalent to <form method="get"> as it defaults to a GET method if POST isn't implied.
Check for errors with error reporting also:
http://php.net/manual/en/function.error-reporting.php
Although, if your form does not have a POST method as I already mentioned, you won't get errors for it, strangely enough.
Sidenote about $userUsername.
That is ambiguous. If you are trying to run a query against that variable, you would need to use a WHERE clause.
I.e.: WHERE column = '$userUsername'