使用 mysqli 来自数据库的单个结果 [英] Single result from database using mysqli

问题描述

我第一次尝试使用 mySQLi.我已经在循环的情况下做到了.循环结果正在显示，但当我尝试显示单个记录时卡住了.这是有效的循环代码.

I am trying to use mySQLi for the first time. I have done it in the case of loop. Loop results are showing but I am stuck when I try to show a single record. Here is loop code that is working.

<?php
// Connect To DB
$hostname="localhost";
$database="mydbname";
$username="root";
$password="";

$conn = mysqli_connect($hostname, $username, $password, $database);
?>

<?php
$query = "SELECT ssfullname, ssemail FROM userss ORDER BY ssid";
$result = mysqli_query($conn, $query);
$num_results = mysqli_num_rows($result);
?>

<?php
/*Loop through each row and display records */
for($i=0; $i<$num_results; $i++) {
$row = mysqli_fetch_assoc($result);
?>

Name: <?php print $row['ssfullname']; ?>
<br />
Email: <?php print $row['ssemail']; ?>
<br /><br />

<?php 
// end loop
} 
?>

如何从第一行或其他任何内容显示单个记录、任何记录、姓名或电子邮件，仅显示单个记录，我该怎么做?在单条记录的情况下，考虑删除上述所有循环部分，让我们显示没有循环的任何单条记录.

How do I show a single record, any record, name, or email, from the first row or whatever, just a single record, how would I do that? In a single record case, consider all the above loop part removed and let's show any single record without a loop.

推荐答案

当只需要一个结果时，不应使用循环.立即获取该行.

When just a single result is needed, then no loop should be used. Just fetch the row right away.

• 如果您需要将整行提取到关联数组中:

• In case you need to fetch the entire row into associative array:

  $row = $result->fetch_assoc();

如果你只需要一个值

in case you need just a single value

  $row = $result->fetch_row();
  $value = $row[0] ?? false;

最后一个示例将返回第一行返回的第一列，如果没有返回行，则返回 false.也可以缩短为一行，

The last example will return the first column from the first returned row, or false if no row was returned. It can be also shortened to a single line,

$value = $result->fetch_row()[0] ?? false;

以下是不同用例的完整示例

Below are complete examples for different use cases

如果要在查询中使用变量，则必须使用准备好的语句.例如，假设我们有一个变量 $id:

When variables are to be used in the query, then a prepared statement must be used. For example, given we have a variable $id:

$query = "SELECT ssfullname, ssemail FROM userss WHERE id=?";
$stmt = $conn->prepare($query);
$stmt->bind_param("s", $id);
$stmt->execute();
$result = $stmt->get_result();
$row = $result->fetch_assoc();

// in case you need just a single value
$query = "SELECT count(*) FROM userss WHERE id=?";
$stmt = $conn->prepare($query);
$stmt->bind_param("s", $id);
$stmt->execute();
$result = $stmt->get_result();
$value = $result->fetch_row()[0] ?? false;

上述过程的详细解释可以在我的文章中找到.至于为什么你必须遵循它在这个著名的问题

The detailed explanation of the above process can be found in my article. As to why you must follow it is explained in this famous question

在您的情况下，查询中没有要使用的变量，您可以使用 query() 方法:

In your case, where no variables to be used in the query, you can use the query() method:

$query = "SELECT ssfullname, ssemail FROM userss ORDER BY ssid";
$result = $conn->query($query);
// in case you need an array
$row = $result->fetch_assoc();
// OR in case you need just a single value
$value = $result->fetch_row()[0] ?? false;

顺便说一句，虽然在学习时使用原始 API 是可以的，但将来考虑使用一些数据库抽象库或至少一个辅助函数:

By the way, although using raw API while learning is okay, consider using some database abstraction library or at least a helper function in the future:

// using a helper function
$sql = "SELECT email FROM users WHERE id=?";
$value = prepared_select($conn, $sql, [$id])->fetch_row[0] ?? false;

// using a database helper class
$email = $db->getCol("SELECT email FROM users WHERE id=?", [$id]);

如您所见，虽然辅助函数可以减少代码量，但类的方法可以将所有重复的代码封装在里面，让您只编写有意义的部分——查询、输入参数和所需的结果格式(以方法名称的形式).

As you can see, although a helper function can reduce the amount of code, a class' method could encapsulate all the repetitive code inside, making you to write only meaningful parts - the query, the input parameters and the desired result format (in the form of the method's name).

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