Fetch modes and styles in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to fetch a row as an associative array using PDO.

PHP

<?php
$stmt = $pdo->query('SELECT * FROM users');
$row = $stmt->fetch([1]);
print_r($row);
?>

Drag options to blanks, or click blank then click option'

APDO::FETCH_BOTH

BPDO::FETCH_NUM

CPDO::FETCH_ASSOC

DPDO::FETCH_OBJ

Attempts:

3 left

💡 Hint

Common Mistakes

Using PDO::FETCH_OBJ returns an object, not an array.

PDO::FETCH_ASSOC fetches the row as an associative array with column names as keys.

2fill in blank

medium

Complete the code to fetch all rows as objects using PDO.

PHP

<?php
$stmt = $pdo->query('SELECT * FROM products');
$rows = $stmt->fetchAll([1]);
foreach ($rows as $product) {
    echo $product->name . "\n";
}
?>

Drag options to blanks, or click blank then click option'

APDO::FETCH_OBJ

BPDO::FETCH_ASSOC

CPDO::FETCH_NUM

DPDO::FETCH_BOTH

Attempts:

3 left

💡 Hint

Common Mistakes

Using PDO::FETCH_ASSOC returns arrays, not objects.

PDO::FETCH_OBJ fetches rows as objects, allowing property access like $product->name.

3fill in blank

hard

Fix the error in the code to fetch a numeric array from the database.

PHP

<?php
$stmt = $pdo->query('SELECT id, price FROM items');
$row = $stmt->fetch([1]);
echo $row[0] . ' costs ' . $row[1];
?>

Drag options to blanks, or click blank then click option'

APDO::FETCH_BOTH

BPDO::FETCH_OBJ

CPDO::FETCH_ASSOC

DPDO::FETCH_NUM

Attempts:

3 left

💡 Hint

Common Mistakes

Using PDO::FETCH_ASSOC causes $row[0] to be undefined.

PDO::FETCH_NUM fetches the row as a numeric array, so $row[0] and $row[1] work correctly.

4fill in blank

hard

Fill both blanks to fetch rows as both numeric and associative arrays.

PHP

<?php
$stmt = $pdo->query('SELECT username, email FROM members');
$row = $stmt->fetch([1] | [2]);
print_r($row);
?>

Drag options to blanks, or click blank then click option'

APDO::FETCH_ASSOC

BPDO::FETCH_OBJ

CPDO::FETCH_NUM

DPDO::FETCH_BOTH

Attempts:

3 left

💡 Hint

Common Mistakes

Using PDO::FETCH_OBJ does not provide array keys.

Combining PDO::FETCH_ASSOC and PDO::FETCH_NUM fetches both keys and numeric indexes, same as PDO::FETCH_BOTH.

5fill in blank

hard

Fill all three blanks to fetch rows as objects and access a property.

PHP

<?php
$stmt = $pdo->query('SELECT id, title FROM books');
$rows = $stmt->fetchAll([1]);
foreach ($rows as [2]) {
    echo [3]->title . "\n";
}
?>

Drag options to blanks, or click blank then click option'

APDO::FETCH_ASSOC

B$book

C$b

DPDO::FETCH_OBJ

Attempts:

3 left

💡 Hint

Common Mistakes

Using PDO::FETCH_ASSOC returns arrays, so ->title would cause error.

PDO::FETCH_OBJ fetches rows as objects. Using $book as the loop variable allows accessing $book->title.

Practice

1. Which PHP PDO fetch mode returns each row as an associative array with column names as keys?

easy

A. PDO::FETCH_OBJ

B. PDO::FETCH_NUM

C. PDO::FETCH_ASSOC

D. PDO::FETCH_COLUMN

Solution

1. Step 1: Understand fetch modes

   PDO::FETCH_ASSOC returns rows as associative arrays with column names as keys.

2. Step 2: Compare with other modes

   PDO::FETCH_NUM returns numeric arrays, PDO::FETCH_OBJ returns objects, PDO::FETCH_COLUMN returns a single column value.

3. Final Answer:

   PDO::FETCH_ASSOC -> Option C

4. Quick Check:

   Associative array = PDO::FETCH_ASSOC [OK]

Hint: Associative arrays use PDO::FETCH_ASSOC for column-name keys [OK]

Common Mistakes:

• Confusing PDO::FETCH_NUM with associative arrays
• Using PDO::FETCH_OBJ when array is needed
• Thinking PDO::FETCH_COLUMN returns full rows

2. Which of the following is the correct syntax to fetch a single row as an object using PDO?

easy

A. $stmt->fetch(PDO::FETCH_OBJ);

B. $stmt->fetch(PDO::FETCH_ASSOC);

C. $stmt->fetchAll(PDO::FETCH_OBJ);

D. $stmt->fetchColumn();

Solution

1. Step 1: Identify fetch method for single row as object

   fetch() returns one row; PDO::FETCH_OBJ returns it as an object.

2. Step 2: Check other options

   fetchAll() returns all rows, fetchColumn() returns a single column value, fetch(PDO::FETCH_ASSOC) returns an associative array.

3. Final Answer:

   $stmt->fetch(PDO::FETCH_OBJ); -> Option A

4. Quick Check:

   Single row object = fetch(PDO::FETCH_OBJ) [OK]

Hint: Use fetch(PDO::FETCH_OBJ) for one row as object [OK]

Common Mistakes:

• Using fetchAll() when only one row is needed
• Using fetchColumn() to get full row
• Confusing FETCH_ASSOC with FETCH_OBJ

3. What will be the output of the following PHP code?

$stmt = $pdo->query('SELECT id, name FROM users LIMIT 1');
$row = $stmt->fetch(PDO::FETCH_NUM);
echo $row[0] . ', ' . $row[1];

medium

A. id, name

B. 1, Alice

C. Array, Array

D. Error: Undefined index

Solution

1. Step 1: Understand PDO::FETCH_NUM

   fetch(PDO::FETCH_NUM) returns a numeric array with column values indexed 0,1,...

2. Step 2: Analyze echo statement

   $row[0] is the first column (id), $row[1] is the second column (name). Assuming first user has id=1 and name='Alice', output is '1, Alice'.

3. Final Answer:

   1, Alice -> Option B

4. Quick Check:

   Numeric array indexes = 0,1 values [OK]

Hint: FETCH_NUM returns numeric keys, use indexes 0,1 for columns [OK]

Common Mistakes:

• Expecting column names as keys with FETCH_NUM
• Using associative keys with numeric array
• Assuming fetchColumn returns full row

4. Identify the error in this PHP code snippet that fetches all user names as a single column array:

$stmt = $pdo->query('SELECT name FROM users');
$names = $stmt->fetch(PDO::FETCH_COLUMN);
print_r($names);

medium

A. print_r cannot print arrays

B. PDO::FETCH_COLUMN is invalid fetch mode

C. Query should select id, not name

D. fetch() returns only one value, should use fetchAll()

Solution

1. Step 1: Understand fetch() vs fetchAll()

   fetch() returns a single row or value, fetchAll() returns all rows.

2. Step 2: Check usage of FETCH_COLUMN

   FETCH_COLUMN fetches a single column value per row; to get all names, fetchAll(PDO::FETCH_COLUMN) is needed.

3. Final Answer:

   fetch() returns only one value, should use fetchAll() -> Option D

4. Quick Check:

   fetchAll(PDO::FETCH_COLUMN) gets all column values [OK]

Hint: Use fetchAll(PDO::FETCH_COLUMN) to get all values of one column [OK]

Common Mistakes:

• Using fetch() instead of fetchAll() for multiple rows
• Thinking FETCH_COLUMN fetches all rows automatically
• Misunderstanding print_r usage

5. You want to fetch all rows from a database as objects but only include rows where the 'active' column is true. Which PHP code snippet correctly applies this filter using fetch modes and styles?

hard

A. $rows = $stmt->fetchAll(PDO::FETCH_OBJ); $activeRows = array_filter($rows, fn($r) => $r->active);

B. $rows = $stmt->fetchAll(PDO::FETCH_ASSOC); foreach ($rows as $r) { if ($r['active']) echo $r; }

C. $rows = $stmt->fetchAll(PDO::FETCH_COLUMN); $activeRows = array_filter($rows, fn($r) => $r->active);

D. $rows = $stmt->fetch(PDO::FETCH_OBJ); while ($rows->active) { echo $rows; }

Solution

1. Step 1: Fetch all rows as objects

   fetchAll(PDO::FETCH_OBJ) returns an array of objects, each representing a row.

2. Step 2: Filter rows where 'active' is true

   array_filter with a callback checks the 'active' property on each object, keeping only those with true.

3. Step 3: Check other options

   $rows = $stmt->fetchAll(PDO::FETCH_ASSOC); foreach ($rows as $r) { if ($r['active']) echo $r; } uses associative arrays but does not collect filtered rows properly; $rows = $stmt->fetchAll(PDO::FETCH_COLUMN); $activeRows = array_filter($rows, fn($r) => $r->active); uses FETCH_COLUMN which returns single column values, not objects; $rows = $stmt->fetch(PDO::FETCH_OBJ); while ($rows->active) { echo $rows; } misuses fetch() and while loop.

4. Final Answer:

   $rows = $stmt->fetchAll(PDO::FETCH_OBJ); $activeRows = array_filter($rows, fn($r) => $r->active); -> Option A

5. Quick Check:

   fetchAll(PDO::FETCH_OBJ) + array_filter for property check [OK]

Hint: Use fetchAll(PDO::FETCH_OBJ) then array_filter by property [OK]

Common Mistakes:

• Using fetch() instead of fetchAll() for multiple rows
• Using FETCH_COLUMN when objects are needed
• Trying to filter before fetching all rows