PDO connection setup in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PDO connection code?

Consider the following PHP code that tries to connect to a MySQL database using PDO. What will it output if the connection is successful?

PHP

<?php
try {
  $pdo = new PDO('mysql:host=localhost;dbname=testdb', 'user', 'pass');
  echo 'Connected successfully';
} catch (PDOException $e) {
  echo 'Connection failed: ' . $e->getMessage();
}
?>

A No output

B Connected successfully

C Fatal error: Uncaught Error: Class 'PDO' not found

D Connection failed: SQLSTATE[HY000] [1045] Access denied for user 'user'@'localhost' (using password: YES)

💡 Hint

If the credentials and database exist and are correct, the try block runs without error.

The code tries to create a PDO object with given credentials. If successful, it prints 'Connected successfully'. If it fails, it prints the error message.

❓ Predict Output

intermediate

What error does this PDO connection code raise?

What error will this PHP code produce when trying to connect to a MySQL database with an invalid DSN string?

PHP

<?php
try {
  $pdo = new PDO('mysql:host=localhost;port=wrongport;dbname=testdb', 'user', 'pass');
  echo 'Connected';
} catch (PDOException $e) {
  echo $e->getMessage();
}
?>

A SQLSTATE[HY000] [2002] No such file or directory

B SQLSTATE[HY000] [1045] Access denied for user 'user'@'localhost' (using password: YES)

C Fatal error: Uncaught PDOException: could not find driver

D Connected

💡 Hint

Using an invalid port in the DSN causes a connection failure related to the network or socket.

The DSN has an invalid port, so PDO cannot connect to the MySQL server. This causes a connection error with SQLSTATE[HY000] and error code 2002.

🔧 Debug

advanced

Why does this PDO connection code cause a fatal error?

Examine this PHP code snippet. Why does it cause a fatal error?

PHP

<?php
$pdo = new PDO('mysql:host=localhost;dbname=testdb', 'user', 'pass');
echo $pdo->connect_error;
?>

A PDO objects do not have a 'connect_error' property, causing a fatal error

B The DSN string is invalid, causing a connection failure

C The code is missing a try-catch block, causing a syntax error

D The username or password is incorrect, causing an exception

💡 Hint

PDO does not use 'connect_error' like mysqli does.

PDO does not have a 'connect_error' property. Trying to access it causes a fatal error. PDO uses exceptions to report errors.

📝 Syntax

advanced

Which option correctly sets PDO to throw exceptions on error?

Which of the following code snippets correctly sets the PDO error mode to throw exceptions?

A $pdo->setErrorMode(PDO::ERRMODE_EXCEPTION);

B $pdo->setAttribute(PDO::ERRMODE_EXCEPTION, PDO::ATTR_ERRMODE);

C $pdo->setAttribute(PDO::ATTR_ERRMODE, 'PDO::ERRMODE_EXCEPTION');

D $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

💡 Hint

The method is setAttribute with the error mode constant as the second argument.

Option D uses the correct method and constants. Option D swaps arguments, C uses a non-existent method, and D passes the constant as a string.

🚀 Application

expert

How many items are in the resulting array after this PDO fetchAll call?

Given this PHP code connecting with PDO and fetching all rows, how many items will be in the $rows array?

PHP

<?php
$pdo = new PDO('mysql:host=localhost;dbname=testdb', 'user', 'pass');
$stmt = $pdo->query('SELECT * FROM users WHERE age > 30');
$rows = $stmt->fetchAll(PDO::FETCH_ASSOC);
echo count($rows);
?>

A 1, because fetchAll returns only the first row

B 0, because fetchAll returns an empty array always

C The number of users with age greater than 30 in the database

D An error, because fetchAll requires a parameter

💡 Hint

fetchAll returns all rows matching the query as an array.

The fetchAll method returns all rows matching the query as an array. The count of this array equals the number of matching rows.