How to avoid this PDO exception: Cannot execute queries while other unbuffered queries are active
- by Vittorio Vittori
Hi, I'd like to print a simple table in my page with 3 columns, building name, tags and architecture style. If I try to retrieve the list of building names and arch. styles there is no problem:
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
My problem starts on retreaving the first 5 tags for every building of the query I've just wrote.
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
The query itself works perfectly, but not where I thought to use it:
<?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;
I'm not experienced on queries, so i though something like this, but it throws the error:
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.
What can I do to avoid this? Should I change all and search a different way to get this kind of queries?
