Fetching results (fetch, fetchAll) in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code using fetch()?

Consider the following PHP code that queries a database and fetches one row:

$stmt = $pdo->query('SELECT id, name FROM users ORDER BY id LIMIT 1');
$row = $stmt->fetch(PDO::FETCH_ASSOC);
print_r($row);

What will be printed?

PHP

$stmt = $pdo->query('SELECT id, name FROM users ORDER BY id LIMIT 1');
$row = $stmt->fetch(PDO::FETCH_ASSOC);
print_r($row);

A Array with numeric keys 0 and 1 containing the first user's data

B Array with keys 'id' and 'name' containing the first user's data

C Boolean false

D An error message about fetchAll()

💡 Hint

fetch() returns one row as an associative array if you use PDO::FETCH_ASSOC.

The fetch() method returns the next row from the result set. Using PDO::FETCH_ASSOC returns an associative array with column names as keys.

❓ Predict Output

intermediate

What does fetchAll() return in this PHP example?

Given this PHP code snippet:

$stmt = $pdo->query('SELECT id, name FROM users');
$rows = $stmt->fetchAll(PDO::FETCH_NUM);
print_r($rows);

What is the structure of $rows?

PHP

$stmt = $pdo->query('SELECT id, name FROM users');
$rows = $stmt->fetchAll(PDO::FETCH_NUM);
print_r($rows);

A An array of arrays with numeric keys for each row

B An array of associative arrays with column names as keys

C A single associative array with all rows merged

D Boolean false

💡 Hint

PDO::FETCH_NUM returns numeric keys for columns.

fetchAll(PDO::FETCH_NUM) returns an array of rows, each row is an indexed array with numeric keys.

❓ Predict Output

advanced

What error does this PHP code raise?

Analyze this PHP code snippet:

$stmt = $pdo->query('SELECT id, name FROM users');
$row = $stmt->fetchAll(PDO::FETCH_ASSOC);
print_r($row[0]['nonexistent_column']);

What error will occur?

PHP

$stmt = $pdo->query('SELECT id, name FROM users');
$row = $stmt->fetchAll(PDO::FETCH_ASSOC);
print_r($row[0]['nonexistent_column']);

A No error, prints null

B Fatal error: Call to undefined method fetchAll()

C TypeError because fetchAll returns boolean

D Undefined index notice for 'nonexistent_column'

💡 Hint

Accessing an array key that does not exist triggers a notice.

fetchAll(PDO::FETCH_ASSOC) returns an array of associative arrays. Accessing a missing key triggers an undefined index notice.

❓ Predict Output

advanced

What is the output of this PHP code using fetch() with PDO::FETCH_OBJ?

Consider this PHP code:

$stmt = $pdo->query('SELECT id, name FROM users ORDER BY id LIMIT 1');
$user = $stmt->fetch(PDO::FETCH_OBJ);
echo $user->name;

What will be printed?

PHP

$stmt = $pdo->query('SELECT id, name FROM users ORDER BY id LIMIT 1');
$user = $stmt->fetch(PDO::FETCH_OBJ);
echo $user->name;

A The name of the first user as a string

B An array containing the user's name

C Boolean false

D Fatal error: Cannot access property on non-object

💡 Hint

PDO::FETCH_OBJ returns an object with properties matching column names.

fetch(PDO::FETCH_OBJ) returns an object. Accessing $user->name prints the user's name.

🧠 Conceptual

expert

How many items are in the array returned by fetchAll() after this query?

Given a table products with 5 rows, what is the number of elements in the array returned by this PHP code?

$stmt = $pdo->query('SELECT * FROM products');
$allProducts = $stmt->fetchAll(PDO::FETCH_ASSOC);
echo count($allProducts);

A 0

B 1

C 5

D An error occurs

💡 Hint

fetchAll() returns all rows as an array of arrays.

fetchAll(PDO::FETCH_ASSOC) returns an array with one element per row. Since the table has 5 rows, count() returns 5.