Preventing injection with prepared statements in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to prepare a SQL statement.

PHP

$stmt = $conn->[1]("SELECT * FROM users WHERE id = ?");

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

Aprepare

Bexecute

Cquery

Dfetch

Attempts:

3 left

💡 Hint

Common Mistakes

Using query() instead of prepare() causes no protection against injection.

Calling execute() before prepare() is incorrect.

The prepare method creates a prepared statement to safely execute SQL queries.

2fill in blank

medium

Complete the code to bind a parameter to the prepared statement.

PHP

$stmt->[1]("i", $userId);

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

Aprepare

Bexecute

Cfetch

Dbind_param

Attempts:

3 left

💡 Hint

Common Mistakes

Using execute() instead of bind_param() skips binding variables.

Calling fetch() before execute() is incorrect.

The bind_param method binds variables to the parameter markers in the SQL statement.

3fill in blank

hard

Fix the error in executing the prepared statement.

PHP

$stmt->[1]();

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

Abind_param

Bexecute

Cprepare

Dquery

Attempts:

3 left

💡 Hint

Common Mistakes

Calling prepare() again instead of execute() causes errors.

Using query() on a prepared statement is invalid.

The execute method runs the prepared statement with the bound parameters.

4fill in blank

hard

Fill both blanks to fetch the result from the executed statement.

PHP

$stmt->[1]();
$stmt->[2]($name);

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

Astore_result

Bfetch

Cbind_result

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Calling fetch() before execute() causes errors.

Not binding results makes it impossible to read data.

First, execute() runs the statement, then bind_result() binds variables to the columns in the result set.

5fill in blank

hard

Fill all three blanks to safely query and fetch a user's name by id.

PHP

$stmt = $conn->[1]("SELECT name FROM users WHERE id = ?");
$stmt->[2]("i", $id);
$stmt->[3]();

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

Aprepare

Bbind_param

Cexecute

Dquery

Attempts:

3 left

💡 Hint

Common Mistakes

Using query() instead of prepare() skips safety.

Forgetting to bind parameters leads to injection risks.

Calling execute() before binding parameters causes errors.

This sequence prepares the statement, binds the integer parameter, and executes the query safely.

Practice

1. What is the main purpose of using prepared statements in PHP when working with databases?

easy

A. To allow multiple database connections at once

B. To prevent SQL injection by separating SQL code from user data

C. To automatically format the output of SQL queries

D. To speed up the execution of all SQL queries

Solution

1. Step 1: Understand SQL injection risks

   SQL injection happens when user input is mixed directly with SQL code, allowing attackers to change the query.

2. Step 2: Role of prepared statements

   Prepared statements separate the SQL code from the data, so user input cannot change the query structure.

3. Final Answer:

   To prevent SQL injection by separating SQL code from user data -> Option B

4. Quick Check:

   Prepared statements prevent injection = D [OK]

Hint: Prepared statements separate code and data to stop injection [OK]

Common Mistakes:

• Thinking prepared statements speed up all queries
• Believing they format output automatically
• Confusing with multiple connections

2. Which of the following is the correct way to prepare and execute a statement in PHP PDO to prevent SQL injection?

easy

A. $stmt = $pdo->prepare('SELECT * FROM users WHERE id = ?'); $stmt->execute([$id]);

B. $stmt = $pdo->query('SELECT * FROM users WHERE id = $id');

C. $stmt = $pdo->prepare('SELECT * FROM users WHERE id = $id'); $stmt->execute();

D. $stmt = $pdo->execute('SELECT * FROM users WHERE id = ?'); $stmt->prepare([$id]);

Solution

1. Step 1: Check correct prepare syntax

   Use prepare() with placeholders like ? for parameters.

2. Step 2: Execute with parameters

   Call execute() with an array of values to bind to placeholders.

3. Final Answer:

   $stmt = $pdo->prepare('SELECT * FROM users WHERE id = ?'); $stmt->execute([$id]); -> Option A

4. Quick Check:

   prepare + execute with array = A [OK]

Hint: Use prepare() then execute() with array for safe queries [OK]

Common Mistakes:

• Using query() with variables directly
• Putting variables inside prepare() string
• Calling execute() before prepare()

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

$stmt = $pdo->prepare('SELECT name FROM users WHERE id = ?');
$stmt->execute([2]);
$result = $stmt->fetchColumn();
echo $result;

Assuming the user with id 2 has the name 'Alice'.

medium

A. 2

B. Array

C. Alice

D. Error

Solution

1. Step 1: Understand prepare and execute

   The statement prepares a query with a placeholder and executes it with id = 2.

2. Step 2: Fetch the result

   fetchColumn() returns the first column of the first row, which is the name 'Alice'.

3. Final Answer:

   Alice -> Option C

4. Quick Check:

   fetchColumn returns name 'Alice' = C [OK]

Hint: fetchColumn() returns first column value from executed statement [OK]

Common Mistakes:

• Expecting fetchColumn() to return an array
• Confusing id with name output
• Not passing parameters to execute()

4. Identify the error in this PHP code that uses prepared statements:

$stmt = $pdo->prepare('SELECT * FROM users WHERE email = :email');
$stmt->execute(':email' => $email);

medium

A. execute() should be called before prepare()

B. The placeholder should be a question mark (?) instead of :email

C. prepare() cannot use named placeholders like :email

D. The execute() method argument should be an array, but syntax is incorrect

Solution

1. Step 1: Check placeholder usage

   Named placeholders like :email are valid in prepare statements.

2. Step 2: Check execute() argument syntax

   execute() expects an array, but ':email' => $email is not inside an array here.

3. Final Answer:

   The execute() method argument should be an array, but syntax is incorrect -> Option D

4. Quick Check:

   execute() needs array argument = A [OK]

Hint: Pass parameters as array to execute() [OK]

Common Mistakes:

• Using wrong placeholder style
• Passing parameters without array brackets
• Calling execute() before prepare()

5. You want to insert multiple user records safely using prepared statements in PHP. Which approach correctly prevents SQL injection and efficiently inserts multiple rows?

$users = [
  ['name' => 'John', 'email' => '[e-mail]'],
  ['name' => 'Jane', 'email' => '[e-mail]']
];
// Which code below is correct?

hard

A. foreach ($users as $user) {
$stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (?, ?)');
$stmt->execute([$user['name'], $user['email']]);
}

B. $stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (?, ?)');
$stmt->execute($users);

C. foreach ($users as $user) {
$sql = "INSERT INTO users (name, email) VALUES ('{$user['name']}', '{$user['email']}')";
$pdo->query($sql);
}

D. $sql = 'INSERT INTO users (name, email) VALUES (?, ?)';
$stmt = $pdo->prepare($sql);
$stmt->execute();

Solution

1. Step 1: Check safe insertion of multiple rows

   foreach ($users as $user) { $stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (?, ?)'); $stmt->execute([$user['name'], $user['email']]); } prepares once per iteration and executes with user data safely bound as parameters.

2. Step 2: Analyze other options

   $stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (?, ?)'); $stmt->execute($users); passes array of arrays directly to execute(), which is invalid. foreach ($users as $user) { $sql = "INSERT INTO users (name, email) VALUES ('{$user['name']}', '{$user['email']}')"; $pdo->query($sql); } uses string interpolation risking injection. $sql = 'INSERT INTO users (name, email) VALUES (?, ?)'; $stmt = $pdo->prepare($sql); $stmt->execute(); calls execute() without parameters.

3. Final Answer:

   foreach ($users as $user) { $stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (?, ?)'); $stmt->execute([$user['name'], $user['email']]); } -> Option A

4. Quick Check:

   Prepare and execute per user with parameters = B [OK]

Hint: Prepare inside loop and execute with user data array [OK]

Common Mistakes:

• Passing multidimensional array directly to execute()
• Using string interpolation instead of parameters
• Calling execute() without parameters