Questions about the wording of SQL statements

An issue with SQL statement notation
$search 1 = "Select classroom_id,building_id from Use2
WHERE (time = ' {$time} ')
and (building_id = ' {$building _id} ')
and (lesson_id like ' $lesson _id ') ";

$result 1 = mysql_query ($search 1, $con);

$row = mysql_fetch_array ($result 1);
$search 2 = "SELECT * FROM Classroom2
WHERE (building_id = ' {$building _id} ')
and * not in
(SELECT * from Classroom2
WHERE (building_id = ' {$building _id} ')
and (classroom_id = ' ${row[' classroom_id ']} ') ";
$result 2 = mysql_query ($search 2);


while ($row = Mysql_fetch_array ($result 2))
{}

Show mysql_fetch_array () expects parameter 1 to being resource, boolean given in D:\xampp\htdocs\search_free2.php
Use2 contains information about the use of classrooms, including the time used for each class, the classroom number, which building, etc.
And now the implementation is the input building number, time to find the function of the empty classroom, I first look at the information I entered, see at such a time in the use2 there are no classroom-related information, if all have no relevant implementation no problem.
This is a bit of a problem if there is no implementation. I think if not, I will first find the classrooms without relevant information and then process the classrooms with relevant information. But to find the classroom without relevant information, it shows the error, please advise!

------Solution--------------------
$result 1 = mysql_query ($search 1, $con) or Die (Mysql_error ());
$result 2 = mysql_query ($search 2) or Die (Mysql_error ());

What errors are indicated.

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