問題描述

我正在過渡到 PDO 準備好的語句，但我在使用 WHILE 語句的基本 SELECT 查詢的語法方面遇到了問題.

I'm transitioning over to PDO prepared statements, and I'm having trouble with the syntax for a basic SELECT query with a WHILE statement.

下面的 foreach 語句回顯了正確的結果，但是 PDO::FETCH_ASSOC 查詢跳過了返回的第一個結果(因此它總是回顯小于它的一個結果應該).

The foreach statement below echos the correct results, but the PDO::FETCH_ASSOC query is skipping the 1rst result that's returned (so it always echo's one result less than it should).

PDO::FETCH_ASSOC

$stmt = $conn->prepare("SELECT * FROM products"); 
$stmt->execute();
$row = $stmt->fetch();
while($row = $stmt->fetch(PDO::FETCH_ASSOC)) { 
    echo $row['product_name'].' '.$row['price'].' '.$row['color'], "<br />"; 
}

foreach

foreach($conn->query('SELECT * FROM products') as $row) {
    echo $row['product_name'].' '.$row['price'].' '.$row['color'], "<br />";  
}

推薦答案

您已經在 while 循環之前獲取了第一行 $row = $stmt->fetch();.如果您刪除此行，它將按預期工作.

You already fetched the first row before the while loop $row = $stmt->fetch();. If you remove this line, it will work as expected.

由于 while 循環會在每次迭代時覆蓋 $row，看起來您是從第二行開始的，但實際發生的是 $row 的值在首先覆蓋 while 循環迭代.

Since the while loop will overwrite $row on each iteration, it looks like you start with the second row, but what happens is the value of $row at the first while loop iteration is overwritten.

要讓循環按照您編寫的方式工作，您需要使用 do-while 構造:

To have the loop work the way you have written, you would need to use a do-while construct:

$row = $stmt->fetch();
do {
     echo $row['product_name'].' '.$row['price'].' '.$row['color'], "<br />";
} while($row = $stmt->fetch(PDO::FETCH_ASSOC));

這里首先打印$row的值，然后被while條件覆蓋.

Here the value of $row will be printed first, before it is overwritten by the while condition.

在這種特殊情況下，當沒有任何結果時，我不想回顯任何內容

In this particular case I don't want to echo anything when there aren't any results

如果是這種情況，請先檢查您的查詢是否返回了任何結果.在這里，我在檢查中是明確的，因為如果您刪除外部 if，您的 while 循環仍會遵循您的意圖 - 也就是說，它不會回顯任何內容如果沒有任何結果.

If that's the case, then check to see if your query returned any results first. Here I'm being explicit in the check, because if you removed the outer if, your while loop would still follow your intentions - that is, it won't echo anything if there aren't any results.

但是，在您的代碼中有明確的意圖總是好的:

However, it is always good to have clear intent in your code:

if ($stmt->columnCount()) {
   while($row = $stmt->fetch(PDO::FETCH_ASSOC)) { 
       echo $row['product_name'].' '.$row['price'].' '.$row['color'], "<br />"; 
   }
}

這篇關于此 PDO::FETCH_ASSOC` 查詢跳過返回的第一個結果的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！