mysql query 2 tables with count - php

Question

Hi i have the following query/table from a local bookstore
$queryadmin ="SELECT last_name, first_name, user_id FROM users";
$recordz = #mysqli_query ($dbc, $queryadmin);
while ($row = mysqli_fetch_array($recordz, MYSQLI_ASSOC)) {
echo '<tr>
<td align="left">' . $row['first_name'] . '</td>
<td align="left">' . $row['last_name'] . '</td>
<td align="left">' . $row['user_id'] . '</td>
</tr>'
;}
now i want an additional column from another table where the numbers of books each user has lend out are displayed.
So the query if nested seperately would go something like this
$query2 = mysql_query("SELECT FROM mirror3 WHERE userid='".$row['user_id']."'", $link);
$anzahl = mysql_num_rows($query2);
placing this query nested inside the while query (right after while starting) from above does not work. How to do that?
supplied argument is not a valid MySQL
result resource
thanks

Answer 1

Your query is wrong. Specify a field name:
$query2 = mysql_query("SELECT
SOMETHING FROM mirror3 WHERE userid='".$row['user_id']."'", $link);

Answer 2

You could probably do this in one query:
$query = mysqli_query('SELECT u.last_name, u.first_name, u.user_id, m.PUT_SOMETHING_HERE
FROM users u
LEFT JOIN mirror3 m ON u.user_id = m.userid
WHERE m.PUT_SOMETHING_HERE IS NOT NULL');
But Parkyprg has a point, you need to be selecting something from that second query.