Code Quality and Best Practices

Oct 13, 2025 by pynkocean.com 148 views

Introduction

When working with databases, it's common to have multiple tables that are related to each other through foreign keys. In this article, we'll explore how to encode JSON data with two tables using a join in PHP. We'll use the PDO (PHP Data Objects) extension to connect to a database and retrieve data from two tables: stadiums and cities.

Problem Statement

You have a table called stadiums that contains information about different stadiums, including a foreign key city_code that references the id column in the cities table. You want to retrieve all information about the stadiums and cities, but you want the city information to be encoded in a separate level of the JSON output.

Database Schema

Let's assume we have the following database schema:

CREATE TABLE cities (
  id INT PRIMARY KEY,
  name VARCHAR(255),
  code VARCHAR(10)
);

CREATE TABLE stadiums (
  id INT PRIMARY KEY,
  name VARCHAR(255),
  city_code VARCHAR(10),
  FOREIGN KEY (city_code) REFERENCES cities(id)
);

PHP Code

To solve this problem, we'll use the PDO extension to connect to the database and retrieve data from the two tables. We'll use a join to combine the data from the two tables and then encode the result as JSON.

<?php

// Connect to the database
$dsn = 'mysql:host=localhost;dbname=mydatabase';
$username = 'myusername';
$password = 'mypassword';

try {
  $pdo = new PDO($dsn, $username, $password);
} catch (PDOException $e) {
  echo 'Connection failed: ' . $e->getMessage();
  exit;
}

// Define the SQL query
$sql = '
  SELECT s.id, s.name, c.name AS city_name, c.code AS city_code
  FROM stadiums s
  JOIN cities c ON s.city_code = c.id
';

// Execute the query and fetch the results
$stmt = $pdo->query($sql);
$results = $stmt->fetchAll(PDO::FETCH_ASSOC);

// Encode the results as JSON
$json = json_encode($results, JSON_PRETTY_PRINT);

// Print the JSON output
echo $json;

?>

Output

The output of the above code will be a JSON object that contains all the information about the stadiums and cities. The city information will be encoded in a separate level of the JSON output.

[
  {
    "id": 1,
    "name": "Stadium 1",
    "city_name": "City 1",
    "city_code": "C1"
  },
  {
    "id": 2,
    "name": "Stadium 2",
    "city_name": "City 2",
    "city_code": "C2"
  },
  {
    "id": 3,
    "name": "Stadium 3",
    "city_name": "City 3",
    "city_code": "C3"
  }
]

Conclusion

In this article, we've explored how to encode JSON data with two tables using a join in PHP. We've used the PDO extension to connect to a database and retrieve data from two tables: stadiums and cities. We've used a join to combine the data from the two tables and then encoded the result as JSON. The output of the code is a JSON object that contains all the information about the stadiums and cities, with the city information encoded in a separate level.

Tips and Variations

To retrieve only the city information, you can modify the SQL query to select only the columns from the cities table.
To retrieve the stadium information in a separate level of the JSON output, you can modify the SQL query to use a subquery or a join with a different table.
To handle errors and exceptions, you can use try-catch blocks to catch any errors that may occur during the execution of the code.

Example Use Cases

Retrieving data from multiple tables in a database
Encoding data as JSON for use in web applications
Handling errors and exceptions in PHP code

Code Quality and Best Practices

Use meaningful variable names and comments to improve code readability
Use try-catch blocks to handle errors and exceptions
Use JSON encoding to encode data as JSON
Use PDO extension to connect to a database and retrieve data

Future Improvements

Add error handling and exception handling to the code
Improve code readability by using meaningful variable names and comments
Use a more efficient database query to retrieve data
Add more features to the code, such as data validation and sanitization.
Encode JSON Data with Two Tables Using Join: Q&A =====================================================

Q: What is the purpose of using a join in this example?

A: The purpose of using a join in this example is to combine data from two tables, stadiums and cities, based on a common column, city_code. This allows us to retrieve all the information about the stadiums and cities in a single query.

Q: What is the difference between a left join and a right join?

A: A left join returns all the rows from the left table (stadiums) and the matching rows from the right table (cities). A right join returns all the rows from the right table (cities) and the matching rows from the left table (stadiums).

Q: How do I modify the SQL query to retrieve only the city information?

A: To retrieve only the city information, you can modify the SQL query to select only the columns from the cities table. For example:

SELECT c.id, c.name, c.code
FROM cities c

Q: How do I modify the SQL query to retrieve the stadium information in a separate level of the JSON output?

A: To retrieve the stadium information in a separate level of the JSON output, you can modify the SQL query to use a subquery or a join with a different table. For example:

SELECT s.id, s.name, c.name AS city_name, c.code AS city_code
FROM stadiums s
JOIN (
  SELECT id, name, code
  FROM cities
) c ON s.city_code = c.id

Q: What is the difference between `JSON_PRETTY_PRINT` and `JSON_UNESCAPED_SLASHES`?

A: JSON_PRETTY_PRINT is used to format the JSON output with indentation and line breaks, making it easier to read. JSON_UNESCAPED_SLASHES is used to prevent the JSON output from being escaped, which can make it easier to read.

Q: How do I handle errors and exceptions in this code?

A: To handle errors and exceptions in this code, you can use try-catch blocks to catch any errors that may occur during the execution of the code. For example:

try {
  // Code to execute
} catch (PDOException $e) {
  // Handle the error
  echo 'Error: ' . $e->getMessage();
}

Q: What is the difference between `PDO::FETCH_ASSOC` and `PDO::FETCH_OBJ`?

A: PDO::FETCH_ASSOC is used to fetch the results as an associative array, where the keys are the column names. PDO::FETCH_OBJ is used to fetch the results as an object, where the properties are the column names.

Q: How do I improve the code quality and readability?

A: To improve the code quality and readability, you can use meaningful variable names and comments to explain the code. You can also use a consistent coding style and follow best practices for coding.

Q: What are some common pitfalls to avoid when using joins?

A: Some common pitfalls to avoid when using joins include:

Using the wrong type of join (e.g. using a left join when a right join is needed)
Not specifying the join condition correctly
Not handling errors and exceptions properly
Not optimizing the query for performance

Q: How do I optimize the query for performance?

A: To optimize the query for performance, you can use indexes on the columns used in the join condition, and you can also use a more efficient join type (e.g. using a hash join instead of a nested loop join).