Insert, update, delete operations in PHP - Mini Project: Build & Apply

Insert, update, delete operations

📖 Scenario: You are managing a small library system. You need to keep track of books using PHP arrays. You will add new books, update existing book details, and remove books when they are no longer available.

🎯 Goal: Build a PHP script that performs insert, update, and delete operations on an array representing books in a library.

📋 What You'll Learn

Create an associative array called $books with specific book entries

Add a new book entry to the $books array

Update the author of an existing book in the $books array

Delete a book entry from the $books array

Print the final $books array

💡 Why This Matters

🌍 Real World

Managing collections of data like books, users, or products often requires adding, updating, and deleting entries in arrays or databases.

💼 Career

Understanding how to manipulate data structures is essential for backend development, data processing, and building dynamic applications.

1

Create the initial books array

Create an associative array called $books with these exact entries: '1984' => 'George Orwell', 'To Kill a Mockingbird' => 'Harper Lee', and 'The Great Gatsby' => 'F. Scott Fitzgerald'.

PHP

# Create the initial books array
# Your code here

Hint

Use square brackets [] to create an associative array with book titles as keys and authors as values.

2

Add a new book entry

Add a new book entry to the $books array with the key 'Brave New World' and the value 'Aldous Huxley'.

PHP

 'George Orwell',
    'To Kill a Mockingbird' => 'Harper Lee',
    'The Great Gatsby' => 'F. Scott Fitzgerald'
];
# Add the new book 'Brave New World' by 'Aldous Huxley' below
# Your code here

Hint

Use the syntax $array['key'] = 'value'; to add a new entry to an associative array.

3

Update an existing book author

Update the author of the book '1984' in the $books array to 'Eric Arthur Blair'.

PHP

 'George Orwell',
    'To Kill a Mockingbird' => 'Harper Lee',
    'The Great Gatsby' => 'F. Scott Fitzgerald'
];
$books['Brave New World'] = 'Aldous Huxley';
# Update the author of '1984' to 'Eric Arthur Blair' below
# Your code here

Hint

To update a value, assign a new value to the existing key like $array['key'] = 'new value';.

4

Delete a book entry and print the array

Remove the book 'The Great Gatsby' from the $books array using the unset() function. Then print the $books array using print_r().

PHP

 'George Orwell',
    'To Kill a Mockingbird' => 'Harper Lee',
    'The Great Gatsby' => 'F. Scott Fitzgerald'
];
$books['Brave New World'] = 'Aldous Huxley';
$books['1984'] = 'Eric Arthur Blair';
# Remove 'The Great Gatsby' from the array
# Print the $books array
# Your code here

Hint

Use unset($array['key']); to delete an entry. Use print_r($array); to display the array.

Practice

1. Which SQL statement is used in PHP to add new data into a database table?

easy

A. UPDATE

B. INSERT INTO

C. DELETE FROM

D. SELECT

Solution

1. Step 1: Understand the purpose of each SQL command

   INSERT INTO adds new rows, UPDATE changes existing rows, DELETE FROM removes rows, and SELECT retrieves data.

2. Step 2: Match the command to adding new data

   Since adding new data means inserting new rows, the correct command is INSERT INTO.

3. Final Answer:

   INSERT INTO -> Option B

4. Quick Check:

   Insert = Add new data [OK]

Hint: Insert adds new rows; update and delete modify existing ones [OK]

Common Mistakes:

• Confusing UPDATE with INSERT
• Thinking DELETE adds data
• Using SELECT to add data

2. Which of the following is the correct PHP syntax to update a user's email in a MySQL database using mysqli_query?

easy

A. $sql = "DELETE FROM users SET email = '[e-mail]' WHERE id = 1";

B. $sql = "INSERT INTO users email = '[e-mail]' WHERE id = 1";

C. $sql = "SELECT email = '[e-mail]' FROM users WHERE id = 1";

D. $sql = "UPDATE users SET email = '[e-mail]' WHERE id = 1";

Solution

1. Step 1: Identify the correct SQL syntax for updating

   The correct syntax for updating is UPDATE table SET column = value WHERE condition.

2. Step 2: Check each option's syntax

   $sql = "UPDATE users SET email = '[e-mail]' WHERE id = 1"; matches the correct syntax. Options A, B, and D misuse SQL commands or syntax.

3. Final Answer:

   $sql = "UPDATE users SET email = '[e-mail]' WHERE id = 1"; -> Option D

4. Quick Check:

   Update syntax = UPDATE ... SET ... WHERE ... [OK]

Hint: Update uses SET with WHERE to change specific rows [OK]

Common Mistakes:

• Using INSERT syntax for update
• Omitting WHERE clause in update
• Using DELETE or SELECT instead of UPDATE

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

$conn = new mysqli('localhost', 'user', 'pass', 'db');
$sql = "DELETE FROM products WHERE id = 10";
if ($conn->query($sql) === TRUE) {
    echo "Deleted successfully";
} else {
    echo "Error deleting record";
}

medium

A. No output

B. Error deleting record

C. Deleted successfully

D. Syntax error

Solution

1. Step 1: Understand the code logic

   The code tries to delete a product with id 10. If the query runs without error, it prints "Deleted successfully".

2. Step 2: Assume the query runs correctly

   Since the SQL syntax is correct and connection is assumed valid, the query returns TRUE, so the success message prints.

3. Final Answer:

   Deleted successfully -> Option C

4. Quick Check:

   Successful DELETE query prints success message [OK]

Hint: If query returns TRUE, success message prints [OK]

Common Mistakes:

• Assuming syntax error without checking code
• Confusing TRUE with FALSE return values
• Ignoring the if-else structure

4. Identify the error in this PHP code that tries to update a user's name:

$sql = "UPDATE users SET name = 'John'";
$conn->query($sql);

medium

A. Missing WHERE clause to specify which user to update

B. Incorrect SQL keyword, should be INSERT

C. Quotes around 'John' should be double quotes

D. Missing semicolon after query execution

Solution

1. Step 1: Review the SQL update statement

   The statement updates the name but does not specify which row to update because it lacks a WHERE clause.

2. Step 2: Understand the impact of missing WHERE

   Without WHERE, all rows in the table will be updated, which is usually unintended and considered an error.

3. Final Answer:

   Missing WHERE clause to specify which user to update -> Option A

4. Quick Check:

   Update without WHERE affects all rows [OK]

Hint: Always include WHERE in update to target specific rows [OK]

Common Mistakes:

• Thinking quotes type causes error
• Confusing UPDATE with INSERT
• Ignoring missing WHERE consequences

5. You want to delete all users from the users table who have not logged in for over a year. Which PHP code snippet correctly performs this operation assuming the last login date is stored in last_login column?

hard

A. $sql = "DELETE FROM users WHERE last_login < DATE_SUB(NOW(), INTERVAL 1 YEAR)";
$conn->query($sql);

B. $sql = "UPDATE users SET last_login = NULL WHERE last_login > DATE_SUB(NOW(), INTERVAL 1 YEAR)";
$conn->query($sql);

C. $sql = "DELETE FROM users WHERE last_login > DATE_ADD(NOW(), INTERVAL 1 YEAR)";
$conn->query($sql);

D. $sql = "INSERT INTO users (last_login) VALUES (DATE_SUB(NOW(), INTERVAL 1 YEAR))";
$conn->query($sql);

Solution

1. Step 1: Understand the condition for deletion

   We want to delete users whose last_login is older than one year, so the condition is last_login < DATE_SUB(NOW(), INTERVAL 1 YEAR).

2. Step 2: Check each option's SQL logic

   $sql = "DELETE FROM users WHERE last_login < DATE_SUB(NOW(), INTERVAL 1 YEAR)"; $conn->query($sql); correctly deletes users with last login older than one year. $sql = "UPDATE users SET last_login = NULL WHERE last_login > DATE_SUB(NOW(), INTERVAL 1 YEAR)"; $conn->query($sql); updates instead of deletes. $sql = "DELETE FROM users WHERE last_login > DATE_ADD(NOW(), INTERVAL 1 YEAR)"; $conn->query($sql); deletes users with last login in the future, which is wrong. $sql = "INSERT INTO users (last_login) VALUES (DATE_SUB(NOW(), INTERVAL 1 YEAR))"; $conn->query($sql); inserts new rows, which is incorrect.

3. Final Answer:

   $sql = "DELETE FROM users WHERE last_login < DATE_SUB(NOW(), INTERVAL 1 YEAR)"; $conn->query($sql); -> Option A

4. Quick Check:

   Delete with condition older than 1 year = $sql = "DELETE FROM users WHERE last_login < DATE_SUB(NOW(), INTERVAL 1 YEAR)"; $conn->query($sql); [OK]

Hint: Use DELETE with WHERE and DATE_SUB for time conditions [OK]

Common Mistakes:

• Using UPDATE instead of DELETE
• Wrong date comparison operators
• Using INSERT instead of DELETE