PHP Basics Quiz

PHP Basics

• PHP (Hypertext Preprocessor) is a server-side scripting language embedded within HTML. It's used to create dynamic web pages and applications.
• PHP code is executed on the server, and the results are sent to the user's web browser as static HTML.
• Key features include:
  • Interpreted language: Code is executed line by line.
  • Support for various databases: PHP can interact with databases like MySQL.
  • Server-side scripting: Dynamic content generation.
• Common tasks PHP handles on a web page include:
  • Processing user input: Handling form submissions.
  • Accessing and manipulating data from databases: Retrieving and updating data.
  • Generating dynamic content: Creating different web pages based on user interaction.
• Essential syntax includes:
  • <?php and ?> tags to enclose PHP code within HTML.
  • Variables: Data storage using keywords like $name.
  • Control structures: if, else if, else, for, while for conditional execution and loop iteration.
  • Functions: Blocks of reusable code.
  • Data types: String, integer, float, boolean.
• Key concepts and aspects:
  • Variables: Store data.
  • Operators: Perform operations like arithmetic, comparison, and logical.
  • Arrays: Store multiple values.
  • Objects: Complex data structures.
  • Error handling: Crucial for robust code.

MySQL Basics

• MySQL is a popular open-source relational database management system (RDBMS). It stores data in tables.
• Relational database organizes data using tables with rows and columns.
• Data is structured with defined schemas to ensure data integrity for related data.
• Key concepts:
  • Database: A collection of related tables.
  • Table: Data is organized in structured format with rows and columns.
  • Row: A single record in a table (i.e., an entry).
  • Column: Each attribute for a record. Defines the properties like name, date of birth etc.
• SQL (Structured Query Language) is the standard language to interact with MySQL.
• Key SQL commands:
  • SELECT: Retrieves data from tables.
  • INSERT: Adds new data to tables.
  • UPDATE: Modifies existing data.
  • DELETE: Removes data from tables.
  • CREATE TABLE: Creates new tables.
  • DROP TABLE: Deletes tables.
  • ALTER TABLE: Modifies existing table structure.
• Data types in MySQL:
  • Integer, Varchar, Date, Float, etc.
• Important aspects:
  • Primary Key: Uniquely identifies each row in a table to enforce data integrity and ensure a unique identifier.
  • Foreign Key: Establishes relationships between tables.
  • Constraints: Used to control and ensure data integrity.

PHP interacting with MySQL

• PHP can connect to and execute SQL queries against a MySQL database.
• A connection to the database is established using PHP's database extension (e.g., mysqli).
• SQL queries are executed using PHP's database functions.
• Results from the SQL query can be processed and displayed to the user.
• Key steps in the process of retrieving data, typically include:
  • Establish a connection to the database.
  • Use mysqli_query to execute SQL query.
  • Fetch results from the query using functions such as mysqli_fetch_assoc or mysqli_fetch_all.
  • Process the fetched data.
  • Close the connection to the database when finished.
• Error handling is vital for preventing crashes and giving useful feedback in situations like incorrect password or unable to connect to the db.

Example: Simple PHP code to retrieve data from MySQL

<?php
// Database credentials
$servername = "localhost";
$username = "your_username";
$password = "your_password";
$dbname = "your_database";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

// SQL query to select data
$sql = "SELECT id, name FROM users";
$result = $conn->query($sql);

// Check for results
if ($result->num_rows > 0) {
    // Output data of each row
    while($row = $result->fetch_assoc()) {
      echo "id: " . $row["id"]. " - Name: " . $row["name"]. "<br>";
    }
} else {
    echo "0 results";
}

$conn->close();
?>

• This example retrieves data from a table named users.
• Replace placeholders with your database credentials.
• The mysqli_fetch_assoc fetches rows as associative arrays.

Security Considerations

• Sanitize user input to prevent SQL injection attacks: Never directly embed user input into SQL queries.
• Use prepared statements with parameterized queries for safer database interactions.
• Secure database credentials: Store securely. Avoid using insecure methods like hardcoding them in the code.