php - MySQL SELECT COUNT 返回 NULL

Question

我正在尝试获取特定项目的评论数量。

$stmt1 = $conn->prepare("SELECT COUNT(r_value) FROM ratings WHERE r_snippet=? AND r_value=3 OR r_value=2");
$stmt2 = $conn->prepare("SELECT COUNT(c_id) FROM comments WHERE c_snippet=?");

foreach ($snippets as $snippet){

    $s_id = $snippet['s_id'];
    $s_thumb = $snippet['s_thumb'];

    $stmt1->bind_param("i",$s_id);
    $stmt1->execute();
    $stmt1->bind_result($numLikes);
    $stmt1->fetch();

    $stmt2->bind_param("i",$s_id);
    $stmt2->execute();
    $stmt2->bind_result($numComments);
    $stmt2->fetch();

?>

    ** HTML here **    

<?php 

}

$stmt1->close();
$stmt2->close();

?>

$numLikes 工作正常，但 $numComments 似乎返回 NULL(来自 var_dump)，我不确定为什么。 phpMyAdmin 中的 SQL 工作正常并返回评论数...

Answer 1

您可能希望为您的第一个查询更改此设置

... AND r_value=3 OR r_value=2

至

... AND (r_value=3 OR r_value=2)

或者这个

... AND r_value IN (2,3)

<小时/>

但是对于第二个查询，尝试一些简单的调试方法

$stmt2 = $conn->prepare("SELECT * FROM comments WHERE c_snippet=10");

然后

$stmt2 = $conn->prepare("SELECT count(*) FROM comments WHERE c_snippet=10");