如何避免此PDO異常：其他無緩衝查詢處於活動狀態時無法執行查詢

Question

我想在我的頁面上打印一個簡單的表格，其列表爲3列，即building name,tags和architecture style。如果我嘗試檢索的building names和arch. styles名單沒有問題：

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 

我的問題上retreaving第5個標籤我剛剛寫了查詢的每一個建設開始。

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 

查詢本身完美的作品，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; 

我不上查詢體驗過，所以我以爲這樣的事情，但它引發錯誤：

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. 

我該怎麼做才能避免這種情況？我應該改變一切，並以不同的方式搜索這種查詢嗎？

你可以真正地再次獲取第一語句循環

Answer 1

你說你發佈了一個簡化版本的代碼。當你在這裏發佈時，你有沒有改變任何東西？當您同時有多個查詢「打開」時，通常會導致此錯誤。例如，您可以撥打fetch()，但在您耗盡前您不會調用它，然後嘗試檢索第二個查詢。

從上面的代碼判斷，這不應該發生，因爲您使用的是fetchAll()。通常，解決此問題的方法是致電closeCursor()[docs]。你可以嘗試在每個fetchAll之後調用它，看看它是否做了什麼。

Answer 2

（注意

$buildings_stmt->fetchAll()調用）：

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

你可能想要做的是獲取$tags_stmt聲明？

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