How to update data using one select in other database table - php

Question

I have two databases and i have one table "TabelaX" in database "Servidor1" with out data and other database "Servidor2" with one table "TabelaY". And i want do one select in table "TabelaY" and with her data do one Update in table "TabelaX" which is in another database. I already made some code but it is not working correctly.
<?php
$conn= mysqli_connect('localhost','root',null,'Servidor2') or die
(mysqli_connect_error());
if (!$conn) {
die("Falha de conexao: ". mysqli_connect_error());
}
$ID = $_POST['ID'];
$sql = "SELECT * FROM TabelaY WHERE ID = $ID";
$result = mysqli_query($conn, $sql);
mysqli_select_db($conn,"Servidor1");
if (mysqli_num_rows($result) > 0) {
while($row = mysqli_fetch_assoc($result)) {
$row1 = $row["ID"];
$row2 = $row["Data"];
}
} else {
echo "0 results";
}
$sql = "INSERT INTO Servidor1.TabelaX (ID, Data)
SELECT ID, Data
FROM Servidor3.TabelaW
WHERE ID = $ID;";
$sql = "UPDATE Servidor1.TabelaX SELECT ID, Data FROM
Servidor3.TabelaW SET Data = $row2 WHERE $row1 = $ID;";
if (mysqli_multi_query($conn, $sql)) {
echo "Dados Inseridos";
} if (mysqli_multi_query($conn, $sql)) {
echo "Dados Atualizados";
}
mysqli_close($conn);

Answer 1

I have no idea what your query is trying to do, because you assign to $sql twice without ever executing the first query, but if you're asking how to update a row in tableX based on data from tableY, then:
UPDATE Servidor1.TabelaX as x, Servidor2.TabelaY as y
SET x.Data = y.Data
WHERE x.id = y.id
AND x.id = $someIdForWhichYouWantToUpdate
Also, do not do this:
$ID = $_POST['ID'];
$sql = "SELECT * FROM TabelaY WHERE ID = $ID";
Imagine what happens when the user posts 1; DROP DATABASE Servidor1 into the form. This is called SQL injection and your code is full of vulnerabilities to it.