Fetching results (fetch, fetchAll) in PHP - Mini Project: Build & Apply

Fetching results using fetch and fetchAll in PHP

📖 Scenario: You are building a simple PHP script to get user data from a database. You want to learn how to fetch one row at a time and how to fetch all rows at once.

🎯 Goal: Learn how to use fetch() and fetchAll() methods to get data from a database query result.

📋 What You'll Learn

Create a PDO connection to an SQLite in-memory database

Create a table called users with columns id, name, and email

Insert three users with exact data

Use fetch() to get one user row

Use fetchAll() to get all user rows

Print the fetched results

💡 Why This Matters

🌍 Real World

Fetching data from databases is a common task in web development. Knowing how to get one row or all rows helps you display data efficiently.

💼 Career

Many jobs require working with databases and PHP. Understanding fetch methods is essential for backend development and data handling.

1

Create the database and insert users

Create a PDO connection called $pdo to an SQLite in-memory database. Then create a table called users with columns id (integer primary key), name (text), and email (text). Insert these three users exactly: (1, 'Alice', '[e-mail]'), (2, 'Bob', '[e-mail]'), and (3, 'Charlie', '[e-mail]').

PHP

<?php
// Create PDO connection and insert users
// Your code here

Hint

Use new PDO('sqlite::memory:') to create the database. Use exec() to run SQL commands.

2

Prepare a SELECT query

Create a variable called $stmt that prepares the SQL query SELECT * FROM users using the $pdo connection.

PHP

setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$pdo->exec("CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT, email TEXT)");
$pdo->exec("INSERT INTO users (id, name, email) VALUES (1, 'Alice', '[e-mail]'), (2, 'Bob', '[e-mail]'), (3, 'Charlie', '[e-mail]')");
// Prepare the SELECT query
// Your code here

Hint

Use $pdo->prepare() with the exact SQL string.

3

Fetch one user row using fetch()

Execute the prepared statement $stmt. Then create a variable called $oneUser that fetches one row using fetch() with PDO::FETCH_ASSOC to get an associative array.

PHP

setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$pdo->exec("CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT, email TEXT)");
$pdo->exec("INSERT INTO users (id, name, email) VALUES (1, 'Alice', '[e-mail]'), (2, 'Bob', '[e-mail]'), (3, 'Charlie', '[e-mail]')");
$stmt = $pdo->prepare('SELECT * FROM users');
// Execute and fetch one row
// Your code here

Hint

Call execute() before fetching. Use fetch(PDO::FETCH_ASSOC) to get one row as an associative array.

4

Fetch all user rows using fetchAll() and print results

Create a variable called $allUsers that fetches all rows using fetchAll() with PDO::FETCH_ASSOC. Then print $oneUser and $allUsers using print_r().

PHP

setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$pdo->exec("CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT, email TEXT)");
$pdo->exec("INSERT INTO users (id, name, email) VALUES (1, 'Alice', '[e-mail]'), (2, 'Bob', '[e-mail]'), (3, 'Charlie', '[e-mail]')");
$stmt = $pdo->prepare('SELECT * FROM users');
$stmt->execute();
$oneUser = $stmt->fetch(PDO::FETCH_ASSOC);
// Fetch all rows and print results
// Your code here

Hint

Use fetchAll(PDO::FETCH_ASSOC) to get all rows as an array of associative arrays. Use print_r() to display arrays.

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