Executing queries with query method in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code using query method?

Consider the following PHP code snippet that uses the query method to fetch data from a database. What will be the output?

PHP

<?php
$mysqli = new mysqli('localhost', 'user', 'pass', 'testdb');
$result = $mysqli->query('SELECT name FROM users WHERE id = 1');
$row = $result->fetch_assoc();
echo $row['name'];
?>

A SyntaxError: Unexpected token in query method

B The name of the user with id 1 is printed

C Fatal error: Call to undefined method query()

D Empty output because query returns false

💡 Hint

Remember that query returns a result object on success, and you can fetch rows from it.

The query method executes the SQL and returns a result object. Using fetch_assoc() retrieves the row as an associative array. Then echo prints the 'name' field.

❓ Predict Output

intermediate

What error does this PHP code raise when using query method?

Look at this PHP code snippet. What error will it produce?

PHP

<?php
$mysqli = new mysqli('localhost', 'user', 'pass', 'testdb');
$result = $mysqli->query('SELECT * FROM non_existing_table');
if (!$result) {
    echo $mysqli->error;
}
?>

A Outputs an error message about unknown table

B SyntaxError: Invalid SQL syntax

C Fatal error: Call to undefined method query()

D No output, query returns empty result

💡 Hint

Check what happens when the query references a table that does not exist.

The query method returns false on failure. The error message from $mysqli->error explains the problem, such as unknown table.

🔧 Debug

advanced

Why does this PHP code using query method cause a fatal error?

Examine this PHP code snippet. It causes a fatal error. What is the cause?

PHP

<?php
$mysqli = new mysqli('localhost', 'user', 'pass', 'testdb');
$result = $mysqli->query('SELECT id FROM users');
echo $result['id'];
?>

A mysqli connection failed causing fatal error

B Query method returns false due to syntax error

C fetch_assoc() method missing causing fatal error

D Trying to access result object as array causes fatal error

💡 Hint

Remember what type query returns and how to access data from it.

The query method returns a result object, not an array. Accessing it like an array causes a fatal error. You must fetch rows first.

📝 Syntax

advanced

Which option correctly uses the query method to fetch all user names?

Choose the PHP code snippet that correctly fetches and prints all user names from the database using the query method.

A

<?php
$result = $mysqli->query('SELECT name FROM users');
while ($row = $result->fetch_assoc()) {
    echo $row['name'] . '\n';
}
?>

B

<?php
$result = $mysqli->query('SELECT name FROM users');
for ($i=0; $i < count($result); $i++) {
    echo $result[$i]['name'] . '\n';
}
?>

C

<?php
$result = $mysqli->query('SELECT name FROM users');
foreach ($result as $row) {
    echo $row['name'] . '\n';
}
?>

D

<?php
$result = $mysqli->query('SELECT name FROM users');
echo $result['name'];
?>

💡 Hint

Think about how to iterate over a mysqli result set properly.

The query method returns a result object. You must use fetch_assoc() in a loop to get each row. Options A, C, and D misuse the result object.

🚀 Application

expert

How many rows are returned by this PHP query method call?

Given this PHP code, how many rows will $count hold after execution?

PHP

<?php
$mysqli = new mysqli('localhost', 'user', 'pass', 'testdb');
$result = $mysqli->query('SELECT * FROM users WHERE age > 30');
$count = $result->num_rows;
?>

A Total number of users in the database

B Always zero because num_rows is not supported

C The number of users with age greater than 30

D One, because query returns only one row by default

💡 Hint

Check what num_rows property represents after a SELECT query.

The num_rows property gives the number of rows in the result set. Here it counts users older than 30.