如何避免此PDO异常：其他无缓冲查询处于活动状态时无法执行查询

Question

我想在我的页面上打印一个简单的表格，其列表为3列，即building name,tags和architecture style。如果我尝试检索的building names和arch. styles名单没有问题：

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 

我的问题上retreaving第5个标签我刚刚写了查询的每一个建设开始。

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 

查询本身完美的作品，但不是我想使用它：

<?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; 

我不上查询体验过，所以我以为这样的事情，但它引发错误：

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. 

我该怎么做才能避免这种情况？我应该改变一切，并以不同的方式搜索这种查询吗？

你可以真正地再次获取第一语句循环

Answer 1

你说你发布了一个简化版本的代码。当你在这里发布时，你有没有改变任何东西？当您同时有多个查询“打开”时，通常会导致此错误。例如，您可以拨打fetch()，但在您耗尽前您不会调用它，然后尝试检索第二个查询。

从上面的代码判断，这不应该发生，因为您使用的是fetchAll()。通常，解决此问题的方法是致电closeCursor()[docs]。你可以尝试在每个fetchAll之后调用它，看看它是否做了什么。

Answer 2

（注意

$buildings_stmt->fetchAll()调用）：

$tags_stmt->execute(); 
$tags = $buildings_stmt->fetchAll (PDO::FETCH_ASSOC); 

你可能想要做的是获取$tags_stmt声明？

$tags_stmt->execute(); 
$tags = $tags_stmt->fetchAll (PDO::FETCH_ASSOC);