模拟 PDO 获取失败情况

SQLSTATE[HY000]: General error: PDO::FETCH_KEY_PAIR fetch mode requires the result set to contain extactly 2 columns.

结论:

• PDOStatement::fetch 如果没有找到记录，则返回 FALSE.
• PDOStatement::fetch 在失败的情况下抛出 - 实际上 - 一个异常.

Conclusion:

• PDOStatement::fetch returns FALSE, if no records are found.
• PDOStatement::fetch throws - indeed - an exception in case of failure.
• 如果没有找到记录，PDOStatement::fetchAll 会返回一个空数组.
• PDO::FETCH_KEY_PAIR 常量未记录在 PDOStatement::fetch 官方页面.
• Instead, PDOStatement::fetchAll returns an empty array, if no records are found.
• The PDO::FETCH_KEY_PAIR constant is not documented on the PDOStatement::fetch official page.

我要感谢所有试图帮助我找到问题答案的用户.你有我的感激之情！

I want to thank to all the users who tried to help me finding the answer to my question. You have my appreciation!

<?php

// Activate error reporting.
error_reporting(E_ALL);
ini_set('display_errors', 1);

try {

    // Create a PDO instance as db connection to a MySQL db.
    $connection = new PDO(
            'mysql:host=localhost;port=3306;dbname=tests;charset=utf8'
            , 'root'
            , 'root'
            , array(
        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
        PDO::ATTR_EMULATE_PREPARES => FALSE,
        PDO::ATTR_PERSISTENT => TRUE
            )
    );

    // Define the sql statement.
    $sql = 'SELECT * FROM users WHERE name = :name';

    /*
     * Prepare the sql statement.
     * 
     * --------------------------------------------------------------------------------
     * If the database server cannot successfully prepare the statement, PDO::prepare() 
     * returns FALSE or emits PDOException (depending on error handling settings).
     * --------------------------------------------------------------------------------
     */
    $statement = $connection->prepare($sql);

    // Validate the preparation of the sql statement.
    if (!$statement) {
        throw new UnexpectedValueException('The sql statement could not be prepared!');
    }

    // Bind the input parameter to the prepared statement.
    $bound = $statement->bindValue(':name', 'Sarah', PDO::PARAM_STR);

    // Validate the binding of the input parameter.
    if (!$bound) {
        throw new UnexpectedValueException('An input parameter can not be bound!');
    }

    /*
     * Execute the prepared statement.
     * 
     * ------------------------------------------------------------------
     * PDOStatement::execute returns TRUE on success or FALSE on failure.
     * ------------------------------------------------------------------
     */
    $executed = $statement->execute();

    // Validate the execution of the prepared statement.
    if (!$executed) {
        throw new UnexpectedValueException('The prepared statement can not be executed!');
    }

    // Fetch the result set.
    $resultset = $statement->fetch(PDO::FETCH_KEY_PAIR);

    // If no records found, define the result set as an empty array.
    if ($resultset === FALSE) {
        $resultset = [];
    }

    // Display the result set.
    var_dump($resultset);

    // Close connection.
    $connection = NULL;
} catch (PDOException $exc) {
    echo '<pre>' . print_r($exc->getMessage(), TRUE) . '</pre>';
    exit();
} catch (Exception $exc) {
    echo '<pre>' . print_r($exc->getMessage(), TRUE) . '</pre>';
    exit();
}

创建表语法:

DROP TABLE IF EXISTS `users`;
CREATE TABLE `users` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(100) DEFAULT NULL,
  `phone` varchar(100) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

插入值语法:

INSERT INTO `users` (`id`, `name`, `phone`)
VALUES
    (1,'Sarah','12345'),
    (2,'John','67890');

表值:

id  name    phone
-----------------
1   Sarah   12345
2   John    67890