INSERT查询在php中使用mysql返回false。 使用msqli_query（$ dbcon，query）

I am trying to INSERT data into a table and I am using mysqli API executing query.

$insert = "INSERT INTO pdhp_patient 
                   (username, password, email, first_name,     
                    last_name, dob, gender, s_s_n, i_n) 
            VALUES ('$username', '$password', '$email', '$first_name', 
                    '$last_name', '$dob', '$gender', '$s_s_n', '$i_n');";

This is the query I am trying to execute.

mysqli_query($connection, $insert); 

The previous line of code is for executing the query. This time the query returns false. I am unable to understand what the mistake is I Have even tried without the single quotes in the query. This however does not work.

Editted:

$username = $_POST['username'];
$password = $_POST['password'];
$email = $_POST['email'];
$first_name = $_POST['first_name'];
$last_name = $_POST['last_name'];
$dob = $_POST['dob'];
$dob = date("m-d-Y", strtotime($dob));
$gender = $_POST['gender'];
$cid = $_POST['country'];
$sid = $_POST['city'];
$s_s_n = $_POST['s_s_n'];
$i_n = $_POST['i_n'];

global $connection;




if(isset($_POST['type']) && $_POST['type']==="patient"){
    $insert = "INSERT INTO pdhp_patient (username, password, email, first_name, last_name, dob, gender, s_s_n, i_n) VALUES ('$username', '$password', '$email', '$first_name', '$last_name', '$dob', '$gender', '$s_s_n', '$i_n');";

    $insert = mysql_prep($insert);

        $result = mysqli_query($connection, $insert); 
if ( $result === false ) {
echo mysqli_error($connection);
exit;
}
        if($val){
        echo "This must be working";
    }else{
        echo "This was not working";
    }
}elseif(isset($_POST['type']) && $_POST['type']==="doctor"){
    $insert = "INSERT INTO pdhp_doctor (username, password, email, first_name, last_name, dob, gender, s_s_n, i_n) VALUES ($username, $password, $email, $first_name, $last_name, $dob, $gender, $s_s_n, $i_n);";
    $insert = mysql_prep($insert);
    mysqli_query($connection, $insert);
}elseif(isset($_POST['environment_radio']) && $_POST['type']==="environment"){
    $insert = "INSERT INTO pdhp_environmentalist (username, password, email, first_name, last_name, dob, gender, s_s_n, i_n) VALUES ($username, $password, $email, $first_name, $last_name, $dob, $gender, $s_s_n, $i_n);";
    $insert = mysql_prep($insert);
    mysqli_query($connection, $insert);
}

Some more code for proper info. This code chunk is what I wanna achieve. this is the full code. Thanks.

Give a man a fish, he eats today. Teach a man to fish, he eats everyday

Add some error checking

$insert = "INSERT INTO pdhp_patient 
                   (username, password, email, first_name,     
                    last_name, dob, gender, s_s_n, i_n) 
            VALUES ('$username', '$password', '$email', '$first_name', 
                    '$last_name', '$dob', '$gender', '$s_s_n', '$i_n');";


$result = mysqli_query($connection, $insert); 
if ( $result === false ) {
    echo mysqli_error($connection);
    exit;
}

Then you can probably fix your own errors

Per your update and comment your issue is that you are escaping the whole query, and not the values that you are passing in. That is not how escaping works, with escaping you escape the values going in incase they contain 's which would break the SQL encapsulation. So instead do..

$username = mysqli_real_escape_string($connection, $_POST['username']);
$password = mysqli_real_escape_string($connection, $_POST['password']);
$email = mysqli_real_escape_string($connection, $_POST['email']);
$first_name = mysqli_real_escape_string($connection, $_POST['first_name']);
$last_name = mysqli_real_escape_string($connection, $_POST['last_name']);
$dob = mysqli_real_escape_string($connection, $_POST['dob']);
$dob = mysqli_real_escape_string($connection, date("m-d-Y", strtotime($dob)));
$gender = mysqli_real_escape_string($connection, $_POST['gender']);
$cid = mysqli_real_escape_string($connection, $_POST['country']);
$sid = mysqli_real_escape_string($connection, $_POST['city']);
$s_s_n = mysqli_real_escape_string($connection, $_POST['s_s_n']);
$i_n = mysqli_real_escape_string($connection, $_POST['i_n']);

and get rid of mysql_prep. You should probably read up a bit more on SQL injections:

http://php.net/manual/en/security.database.sql-injection.php
https://www.owasp.org/index.php/SQL_Injection

The more secure approach is using parameterized queries with prepared statements.

http://php.net/manual/en/mysqli.quickstart.prepared-statements.php