Fetching results (fetch, fetchAll) in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to fetch one row from the PDO statement.

PHP

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

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

Afetch

BfetchAll

Cexecute

Dprepare

Attempts:

3 left

💡 Hint

Common Mistakes

Using fetchAll() when only one row is needed.

Using execute() which runs a statement but does not fetch data.

The fetch() method fetches the next row from the result set.

2fill in blank

medium

Complete the code to fetch all rows from the PDO statement.

PHP

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

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

Afetch

Bexecute

CfetchAll

Dprepare

Attempts:

3 left

💡 Hint

Common Mistakes

Using fetch() when all rows are needed.

Using execute() which does not fetch data.

The fetchAll() method fetches all rows at once as an array.

3fill in blank

hard

Fix the error in fetching rows as associative arrays.

PHP

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

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 FETCH_NUM which returns numeric keys.

Using FETCH_OBJ which returns objects instead of arrays.

Use PDO::FETCH_ASSOC to fetch rows as associative arrays with column names as keys.

4fill in blank

hard

Fill both blanks to fetch rows as objects and print a property.

PHP

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

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

AfetchAll

Bfetch

CPDO::FETCH_OBJ

DPDO::FETCH_ASSOC

Attempts:

3 left

💡 Hint

Common Mistakes

Using fetch() instead of fetchAll() to get all rows.

Using FETCH_ASSOC which returns arrays, not objects.

Use fetchAll(PDO::FETCH_OBJ) to get all rows as objects.

5fill in blank

hard

Fill all three blanks to fetch one row as a numeric array and print the first column.

PHP

<?php
$stmt = $pdo->query('SELECT id, name FROM categories');
$row = $stmt->[1]([2]);
echo $row[[3]];
?>

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

AfetchAll

Bfetch

C0

DPDO::FETCH_NUM

Attempts:

3 left

💡 Hint

Common Mistakes

Using fetchAll() when only one row is needed.

Using FETCH_ASSOC which returns associative arrays.

Using wrong index to access the first column.

Use fetch(PDO::FETCH_NUM) to get one row as a numeric array, then access the first column with index 0.

Practice

1. What does the fetch() method do when used with a PDO statement in PHP?

easy

A. Retrieves one row from the query result

B. Retrieves all rows from the query result

C. Executes the SQL query

D. Closes the database connection

Solution

1. Step 1: Understand the purpose of fetch()

   The fetch() method is designed to get a single row from the result set of a database query.

2. Step 2: Compare with other methods

   Unlike fetchAll(), which retrieves all rows, fetch() only returns one row at a time.

3. Final Answer:

   Retrieves one row from the query result -> Option A

4. Quick Check:

   fetch() = one row [OK]

Hint: fetch() gets one row, fetchAll() gets all rows [OK]

Common Mistakes:

• Confusing fetch() with fetchAll()
• Thinking fetch() executes the query
• Assuming fetch() closes the connection

2. Which of the following is the correct syntax to fetch all rows from a PDO statement $stmt in PHP?

easy

A. $rows = $stmt->fetchAll();

B. $rows = $stmt->fetch_all();

C. $rows = fetchAll($stmt);

D. $rows = $stmt->fetch();

Solution

1. Step 1: Identify the correct method name

   The PDOStatement object uses fetchAll() to retrieve all rows as an array.

2. Step 2: Check method call syntax

   The correct syntax is $stmt->fetchAll(); with camelCase and parentheses.

3. Final Answer:

   $rows = $stmt->fetchAll(); -> Option A

4. Quick Check:

   fetchAll() method syntax correct [OK]

Hint: Use fetchAll() with parentheses on the statement object [OK]

Common Mistakes:

• Using fetch_all() instead of fetchAll()
• Calling fetchAll() as a standalone function
• Using fetch() when fetchAll() is needed

3. Given the following PHP code, what will be the output?

$stmt = $pdo->query('SELECT id FROM users LIMIT 2');
$row1 = $stmt->fetch();
$row2 = $stmt->fetch();
$row3 = $stmt->fetch();
var_dump([$row1, $row2, $row3]);

medium

A. [false, false, false]

B. [array with first row, array with second row, array with third row]

C. [array with first row, array with second row, false]

D. Syntax error

Solution

1. Step 1: Understand fetch() behavior on limited rows

   The query returns 2 rows. Each fetch() call returns one row until no rows remain.

2. Step 2: Analyze each fetch() call

   First fetch() returns first row array, second fetch() returns second row array, third fetch() returns false (no more rows).

3. Final Answer:

   [array with first row, array with second row, false] -> Option C

4. Quick Check:

   fetch() returns false after last row [OK]

Hint: fetch() returns false when no rows left [OK]

Common Mistakes:

• Expecting fetch() to return null instead of false
• Assuming fetch() returns empty array after last row
• Thinking fetch() fetches all rows at once

4. What is wrong with this PHP code snippet?

$stmt = $pdo->query('SELECT name FROM users');
$rows = $stmt->fetch();
foreach ($rows as $row) {
    echo $row['name'];
}

medium

A. fetch() returns all rows, so foreach is unnecessary

B. The variable $rows is not defined

C. The query syntax is invalid

D. fetch() returns a single row, so foreach on it causes error

Solution

1. Step 1: Check what fetch() returns

   fetch() returns a single row as an array, not an array of rows.

2. Step 2: Understand foreach usage

   foreach expects an array of rows, but here it loops over columns of one row, causing errors when accessing $row['name'].

3. Final Answer:

   fetch() returns a single row, so foreach on it causes error -> Option D

4. Quick Check:

   fetch() = one row, foreach needs multiple rows [OK]

Hint: Use fetchAll() when looping over multiple rows [OK]

Common Mistakes:

• Using fetch() when fetchAll() is needed for loops
• Assuming fetch() returns all rows
• Not checking data structure before foreach

5. You want to fetch all users from the database but only keep those whose age is greater than 18. Which code snippet correctly uses fetchAll() with a filter in PHP?

hard

A. $adults = $stmt->fetchAll(fn($r) => $r['age'] > 18);

B. $rows = $stmt->fetchAll();
$adults = array_filter($rows, fn($r) => $r['age'] > 18);

C. $adults = $stmt->fetchAll();
foreach ($adults as $r) {
if ($r['age'] <= 18) unset($r);
}

D. $adults = $stmt->fetch();
while ($r['age'] > 18) { $adults[] = $r; }

Solution

1. Step 1: Fetch all rows first

   Use fetchAll() to get all rows as an array.

2. Step 2: Filter rows by age

   Use array_filter() with a callback to keep only rows where age > 18.

3. Final Answer:

   $rows = $stmt->fetchAll(); $adults = array_filter($rows, fn($r) => $r['age'] > 18); -> Option B

4. Quick Check:

   fetchAll() + array_filter() = filtered rows [OK]

Hint: fetchAll() then filter with array_filter() for conditions [OK]

Common Mistakes:

• Passing a callback directly to fetchAll() (not supported)
• Modifying array inside foreach without reassigning
• Using fetch() when multiple rows needed