How Do I Grab And Put Primary Key Into Foreign Key In Another Table? PHP, MySQL

Question

The tables are Accounts with A_ID (PRIMARY KEY), Username, Password and Messages with M_ID (PRIMARY KEY), Message, A_ID (FOREIGN KEY)

When a person sends a message I am using a SELECT statement to get the person's A_ID where their username = their username and then INSERT it into the table.

The full code is in the Paste below, it is quite messy, please forgive me for that. I'm working on a much cleaner version but I have to get this vital part first.

http://pastebin.com/e3aqGerw

Where I am really stuck is here ¬

if (isset($_POST['SendMessage'])) {
    $GetAID = "SELECT A_ID FROM Accounts WHERE Username='$CookieValue'";
    $ResultAID = $Connect->query($GetAID);
    echo $ResultAID;
    $Message = htmlspecialchars($_POST['Message']);
    $MessageSQL = "INSERT INTO Messages (M_ID, Message, A_ID) VALUES ('', '$Message', '$ResultAID')";

    if ($Connect->query($MessageSQL) === TRUE) {
        echo "Message Sent<BR/>";
    } else {
        echo "Error Sending Message<BR/>";
    }
}

My question is how do I put the A_ID into a variable and then INSERT it into the Messages table as the FOREIGN KEY to Accounts table's A_ID PRIMARY KEY?

Answer 1

The Foreign Key requirement has to be handled on the SQL server. You will need to set up a foreign key restraint.

Inserting the variable is easy.

    $MessageSQL = "INSERT INTO Messages (M_ID, Message, A_ID) VALUES ('', '".$Message."', '".$ResultAID['A_ID']."')";

Answer 2

$SQL = "INSERT INTO Accounts (A_ID, Username, Password) VALUES ('', '$Username', '$PasswordHash')";
$Result = mysqli_query($Connect, $SQL);

$GET_last_ID = mysqli_insert_id($con);

$MessageSQL = "INSERT INTO Messages (M_ID, Message, A_ID) VALUES ('', '$Message', '$GET_last_ID')";

just add the $GET_last_ID = mysqli_insert_id($Connect); below mysqli_query and insert the variable $GET_last_ID to the next table. just like u see above. the code $GET_last_ID = mysqli_insert_id($Connect); will get the lastes inserted primary key id.

hope this help you