how to insert multiple queries in one query to get results

Question

I have written a PHP script for download excel file which contain some MySQL data fetching by a MySQL query. Data is coming correctly. Here is the sample picture. Excel Sheet Now the problem is i am getting codes(id) of two column 'category_cod' and 'material_cod' instead I want to fetch category_name and material_name from category and material tables. Please If anyone have any idea how to achieve that. Here is my code:

<?php
$header = '';
$data = '';
$select = "select * from pdbp inner join bp on(pdbp.bp_id=bp.id)";

//run mysql query and then count number of fields
$export = mysql_query ( $select ) 
   or die ( "Sql error : " . mysql_error( ) );
$fields = mysql_num_fields ( $export );

//create csv header row, to contain table headers 
//with database field names
for ( $i = 0; $i < $fields; $i++ ) {
$header .= mysql_field_name( $export , $i ) . ",";
}

//this is where most of the work is done. 
//Loop through the query results, and create 
 //a row for each
while( $row = mysql_fetch_row( $export ) ) {
$line = '';
//for each field in the row
foreach( $row as $value ) {
    //if null, create blank field
    if ( ( !isset( $value ) ) || ( $value == "" ) ){
        $value = "\t";
    }
    //else, assign field value to our data
    else {
        $value = str_replace( '"' , '""' , $value );
        $value = '"' . $value . '"' . "\t";
    }
    //add this field value to our row
    $line .= $value;
}
//trim whitespace from each row
$data .= trim( $line ) . "\n";
}
//remove all carriage returns from the data
$data = str_replace( "\r" , "" , $data );

$file_name = 'excel_data';
//create a file and send to browser for user to download
header("Content-type: application/vnd.ms-excel");
header( "Content-disposition: filename=".$file_name.".xls");
print "$header\n$data";
exit;
?>

Answer 1

Table bp bp_id material_cod category_cod

table materials material_id material_name

table categories category_id category_name

SELECT material_name, category_name FROM bp 
LEFT JOIN materials ON materials.material_id = bp.material_cod 
LEFT JOIN categories ON categories.categories_id = bp.category_cod