Gostaria de imprimir uma tabela simples na minha página com 3 colunas,building name, tags earchitecture style. Se eu tentar recuperar a lista debuilding names earch. styles não há problema:

SELECT buildings.name, arch_styles.style_name
FROM buildings
INNER JOIN buildings_arch_styles
ON buildings.id = buildings_arch_styles.building_id
INNER JOIN arch_styles
ON arch_styles.id = buildings_arch_styles.arch_style_id
LIMIT 0, 10

Meu problema começa na recauchutagem das 5 primeiras tags para cada construção da consulta que acabei de escrever.

SELECT DISTINCT name
FROM tags
INNER JOIN buildings_tags
ON buildings_tags.tag_id = tags.id
AND buildings_tags.building_id = 123
LIMIT 0, 5

A consulta em si funciona perfeitamente, mas não onde eu pensava em usá-la:

<?php

// pdo connection allready active, i'm using mysql
$pdo_conn->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, true);

$sql = "SELECT buildings.name, buildings.id, arch_styles.style_name
        FROM buildings
        INNER JOIN buildings_arch_styles
        ON buildings.id = buildings_arch_styles.building_id
        INNER JOIN arch_styles
        ON arch_styles.id = buildings_arch_styles.arch_style_id
        LIMIT 0, 10";

$buildings_stmt = $pdo_conn->prepare ($sql);
$buildings_stmt->execute ();
$buildings = $buildings_stmt->fetchAll (PDO::FETCH_ASSOC);

$sql = "SELECT DISTINCT name
        FROM tags
        INNER JOIN buildings_tags
        ON buildings_tags.tag_id = tags.id
        AND buildings_tags.building_id = :building_id
        LIMIT 0, 5";
$tags_stmt = $pdo_conn->prepare ($sql);

$html = "<table>"; // i'll use it to print my table

foreach ($buildings as $building) {
    $name = $building["name"];
    $style = $building["style_name"];
    $id = $building["id"];

    $tags_stmt->bindParam (":building_id", $id, PDO::PARAM_INT);
    $tags_stmt->execute (); // the problem is HERE
    $tags = $tags_stmt->fetchAll (PDO::FETCH_ASSOC);

    $html .= "... $name ... $style";

    foreach ($tags as $current_tag) {
        $tag = $current_tag["name"];
        $html .= "... $tag ..."; // let's suppose this is an area of the table where I print the first 5 tags per building
    }

}
$html .= "...</table>";
print $html;

Eu não sou experiente em consultas, então eu pensei em algo parecido com isto, mas lança o erro:

PHP Fatal error:  Uncaught exception 'PDOException' with message 'SQLSTATE[HY000]: General error: 2014 Cannot execute queries while other unbuffered queries are active.  Consider using PDOStatement::fetchAll().  Alternatively, if your code is only ever going to run against mysql, you may enable query buffering by setting the PDO::MYSQL_ATTR_USE_BUFFERED_QUERY attribute.

O que posso fazer para evitar isso? Devo alterar tudo e procurar uma maneira diferente de obter esse tipo de consulta?