选择时没有匹配行的MySQLi Query返回值 [英] MySQLi Query return value in case of Select with no matching rows

问题描述

我有一个表bank，如下所示:

I have a table bank as follows:

|name|day|time|
|jack| 1 |  2 |

我需要检查name，day和time.现在，即使我更改WHERE条件参数的值，以致找不到匹配的行，它仍然会打印成功".这有什么问题吗?如果我的代码尝试如下:

I need to check for name, day and time. Now, even if I change values of WHERE condition parameters, such that no matching rows are found, it still prints "success". What could be wrong here ? Below if my code attempt:

<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "test";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 

$sql = "SELECT * FROM `bank` WHERE name='jack' AND day='1' AND time='2'";
$result = $conn->query($sql);

if ($result) 
{
        echo "success";
} 
else 
{
    echo "0 results";
}
$conn->close();
?>

推荐答案

来自 MySQLi文档:

失败时返回FALSE.对于成功的SELECT，SHOW，DESCRIBE或EXPLAIN查询，mysqli_query()将返回mysqli_result对象.对于其他成功的查询，mysqli_query()将返回TRUE

Returns FALSE on failure. For successful SELECT, SHOW, DESCRIBE or EXPLAIN queries mysqli_query() will return a mysqli_result object. For other successful queries mysqli_query() will return TRUE

因此，基本上，即使查询不返回任何行，它仍然是成功的查询.您应该检查返回的行数.将您的if条件更改为:

So basically, even if query does not return any rows, it is still a successful query. You should rather check for number of rows returned. Change your if condition to:

If ($result->num_rows) {

边注:

1. 现在是时候使用PHP-MySQL采取正确的初始步骤了.与其使用查询功能，不如使用 Prepared Statements .
2. 始终使用异常处理(try-catch)，以在查询执行期间捕获其他错误.

1. Now is the right time to take correct initial steps in working with PHP-MySQL. Instead of using query function, you should rather use Prepared Statements.
2. Always use Exception handling (try-catch), to catch other errors during query execution.

以下是使用准备好的语句和异常处理的等效代码:

Here is the equivalent code using prepared statements and exception handling:

try {

    // Prepare the query
    $stmt = "SELECT * FROM bank 
             WHERE name = ? 
               AND day = ? 
               AND time = ?";

    // Bind the parameters
    // assuming that your day and time are integer values
    $stmt->bind_param("sii", 'jack', '1', '2');

    // execute the query
    $stmt->execute();

    // Getting results:
    $result = $stmt->get_result();

    if ($result->num_rows === 0) {
        echo "0 results";
    } else {
        echo "success";

        // reading results
        while($row = $result->fetch_assoc()) {
            $name = $row['name'];
            $day = $row['day'];
            $time = $row['time'];
        }
    }

} catch (Exception $e) {

     // your code to handle in case of exceptions here
     // generally you log error details, 
     //and send out specific error message alerts
}

这篇关于选择时没有匹配行的MySQLi Query返回值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！