Question

I’m trying to write an INNER JOIN query. I wanted to get rows/information that are in two different tables. Here’s what I’m trying:

Table Names are: Students and main_table

$sql =mysql_query ("SELECT main_table.maric_no, main_table.academic_session, main_table.semester, 
main_table.course_name, main_table.total, students.first_name, students.last_name, 
students.other_name, students.level 
FROM main_table INNER JOIN students ON 
main_table.matric_no = students.matric_no 
WHERE main_table.matric = mysql_real_escape_string($_POST[matric_no]'"); 

$number_cols = mysql_num_fields($sql); 

Here’s the error message:

ERROR: mysql_num_fields() expects parameter 1 to be resource, boolean given in c:\filepath on line Number..

Where could the problem be coming from?

Answer 1

Two errors at first glance:

1. mysql_real_escape_string() is a php function, not a mysql-function. It is used to make data safer before using it in a mysql-query.
2. Your $_POST-variable isn’t assigned properly.

Format it like this:

$sql = mysql_query("
    SELECT M.maric_no, M.academic_session,  
        M.semester, M.course_name, M.total, 
        S.first_name, S.last_name, 
        S.other_name, S.level 
    FROM main_table M 
    INNER JOIN students S ON M.matric_no = S.matric_no 
    WHERE M.matric = '"
    .mysql_real_escape_string($_POST['matric_no'])
    ."'"); 

I took the liberty to add aliases to the table names, this cleans up your SQL statement quite a lot.

There might be other errors, too (p.e. wrong fields, is your WHERE-statement really on the field main_table.matric and not main_table.matric_no?), but in order to analyze this you’ll need to provide more details about your tables.