Select data from table using data from another table - php

Question

I have 2 tables, one is called companies (with columns: title, finance, address, phone....) and the other is called investments (with columns: title, budget....).
The title value is same in both tables example: google inc as title is stored in both tables.
All I want to do is display data from table "investments" to a page called companies-profile using title as key.
companies-profile page shows data based on id that I get from another page (where all companies are displayed).
I use this code:
<?php
$var1 = "SELECT title
FROM companies
WHERE idcompanies='$ID'";
$result2 = mysqli_query($conn, "SELECT budget
FROM n4399
WHERE title='{$var1}'")
or die(mysqli_error($conn));
$row2 = mysqli_fetch_array($result2);
echo $row2['budget'];
?>
$conn is declared and database conection is ok
i m getting:
You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '2'" at line 1
2 is the id that is selected by the user
Using xamp

Answer 1

You could use a single query
SELECT budget
FROM companies
INNER JOIN n4399 ON companies.Title=n4399.title
WHERE companies.id = ?
and using a proper prepared statement and binding
$stmt = $conn->prepare("SELECT budget
FROM companies
INNER JOIN n4399 ON companies.Title=n4399.title
WHERE companies.id = ?");
$stmt->bind_param("i", $ID);
$stmt->execute();
//
$result = $stmt->get_result();
while($row = $result->fetch_assoc()) {
echo $row['budget'];
}

Answer 2

You are trying to execute the following sql sentence:
SELECT budget
FROM n4399
WHERE title='SELECT title
FROM companies
WHERE idcompanies='$ID''
Either of two: or you first execute the firs sentence (select title from companies...) getting the effective title of the company or you can change your select into this:
SELECT budget
FROM n4399
WHERE title in (SELECT title
FROM companies
WHERE idcompanies='$ID')
So that this select can return all the values that have matching titles in the second select.