Solution to PHP Fatal error: Uncaught exception 'PDOException'

In PHP development, you may encounter errors such as "PHP Fatal error: Uncaught exception 'PDOException'". This is an exception caused by an error when PHP operates the database. If this error is not handled in time, it will cause program interruption or unexpected errors.

So how to solve this problem? Here are some common solutions.

1. Check the database parameters

First, we need to check whether the parameters passed when connecting to the database are correct. We need to confirm that the database address, username and password are correct. You can use the following code to check:

$db_host = 'localhost'; // 数据库地址
$db_name = 'mydb'; // 数据库名称
$db_user = 'myuser'; // 用户名
$db_pwd = 'mypassword'; // 密码

try {
    $dbh = new PDO('mysql:host=' . $db_host . ';dbname=' . $db_name , $db_user, $db_pwd);
    echo "Connected successfully";
} catch (PDOException $e) {
    die("Error!: " . $e->getMessage() . "<br/>");
}

If the database connection information is correct, the code will output "Connected successfully".

2. Check whether the MySQL service is started

If the database connection information is correct, we need to check whether the MySQL service has been started. In Linux systems, you can use the following command to check whether the MySQL service is running:

systemctl status mysql.service

If the MySQL service is not running, you can use the following command to start the MySQL service:

systemctl start mysql.service

3. Check tables and fields Existence

If the MySQL service has been started, we need to check whether the tables and fields in the database exist. It may be caused by misspelling of table name or field name.

We can use the following command to view the table in the database:

SHOW TABLES;

Or use the following command to view the fields in the table:

SELECT column_name
FROM information_schema.columns
WHERE table_name = 'mytable';

4. Check the database encoding

When connecting to the database, we need to confirm whether the database encoding is correct. If the encoding does not match, it will cause problems such as garbled characters when using Chinese.

We can specify the character set when connecting to the database, as shown below:

// 方法一：使用dsn
$dbh = new PDO('mysql:host=localhost;dbname=mydb;charset=utf8mb4;', $db_user, $db_pwd);

// 方法二：使用 exec() 方法设置
$dbh->exec('SET NAMES utf8mb4;');

5. Check whether the PHP extension is installed

Finally, we need to confirm whether the PHP extension is installed . PDOException is a built-in extension of PHP, we need to confirm whether it has been enabled.

We can use the following code to check:

if (!extension_loaded('pdo_mysql')) {
    echo 'PDO MySQL 扩展未加载';
}

If it is not enabled, you can enable the extension in the PHP configuration file php.ini:

extension=pdo_mysql.so

In summary, When we encounter the error "PHP Fatal error: Uncaught exception 'PDOException'", we need to handle it in time. We can solve this problem by checking database parameters, checking whether the MySQL service is started, checking whether tables and fields exist, checking database encoding, and checking whether PHP extensions are installed. hope that it can help us.

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