Question

I’m stuck trying to create a result page that lists details based on a series of masters.

Here’s a sample problem…

Three tables such as those shown below:

Book (id, title)
Author (id, name)
BookAuthors (bookID, authorID)

I wish to generate a list similar to this:

Book Title 1
  Author 1
  Author 2
Book Title 2
  Author 3
Book Title 3
  Author 1
  Author 4

and so on.

I wish to use PHP PDO to achieve this.

[Updated with more detail]

The problem I have is more about how to go about traversing the results from the PDO when nesting prepared statements is not possible…

I was hoping to nest a query within a query and use the results from the 1st query [I’ve extended the query to include a filter on the book titles, but this may be blank thus returning the whole set]:

select id as idBook,title from book where title like %:title%

to then create the list of authors for each book

select name from author, bookauthors 
  where bookauthor.authorid = author.id 
    AND bookauthor.bookid = :idBook:

Where :idBook: is the next book id from the result set from the 1st query.

As the number of books retrieved in the 1st query may be large, I was hoping not to use fetchall if possible…

Anyone got pointers / sample solution code for this?

many thanks in advance!

Answer 1

Instead of multiple queries I’d rather store some state in a php variable. In this case all you need to know is: has the book “changed”, i.e. must the script print the title?

<?php
$pdo = new PDO('mysql:host=localhost;dbname=test', 'localonly', 'localonly', array(PDO::ATTR_ERRMODE=>PDO::ERRMODE_EXCEPTION));
foo($pdo);  // add test data

$r = $pdo->query('
  SELECT
    l.bookID, b.title, a.name
  FROM
    BookAuthor as l
  JOIN
    Author as a
  ON
    a.id=l.authorID 
  JOIN
    Book as b
  ON
    b.id=l.bookID
  ORDER BY
    l.bookID,
    l.authorID
');
$currentBook = null;
foreach($r as $row) {
  if ( $currentBook!=$row['bookID'] ) {
    echo $row['title'], "\n";
    $currentBook=$row['bookID'];
  }
  echo '  ', $row['name'], "\n";
}

function foo($pdo) {
  $pdo->exec('create temporary table Book (id int auto_increment, title varchar(48), primary key(id))');
  $pdo->exec('create temporary table Author (id int auto_increment, name varchar(48), primary key(id))');
  $pdo->exec('create temporary table BookAuthor (bookID int, authorID int)');

  $pdo->exec("INSERT INTO Author (id,name) VALUES (1,'Author1'),(2,'Author2'),(3,'Author3'),(4,'Author4')");
  $pdo->exec("INSERT INTO Book (id,title) VALUES (1,'Book Title 1'),(2,'Book Title 2'),(3,'Book Title 3')");
  $pdo->exec("INSERT INTO BookAuthor (bookID,authorID) VALUES (1,1),(1,2),(2,3),(3,1),(3,4)");
}