An Outer Join is a type of database join (commonly used in SQL) that returns records from one or both tables even if there’s no matching record in the other table.
LEFT OUTER JOIN (or simply: LEFT JOIN):
→ Returns all records from the left table, and the matching ones from the right table.
→ If there’s no match, the result is filled with NULL values from the right table.
RIGHT OUTER JOIN (or: RIGHT JOIN):
→ Returns all records from the right table, and the matching ones from the left table.
→ If there’s no match, NULL is used for the left side.
FULL OUTER JOIN:
→ Returns all records from both tables, with NULL where no match exists on either side.
Suppose you have two tables:
Customers
| CustomerID | Name |
| 1 | Anna |
| 2 | Bernd |
| 3 | Clara |
Orders
| OrderID | CustomerID | Product |
| 101 | 2 | Book |
| 102 | 4 | Lamp |
| CustomerID | Name | OrderID | Product |
|---|---|---|---|
| 1 | Anna | NULL | NULL |
| 2 | Bernd | 101 | Book |
| 3 | Clara | NULL | NULL |
PDO stands for PHP Data Objects and it's a database abstraction layer in PHP. It provides an object-oriented interface to access different types of databases—such as MySQL, PostgreSQL, or SQLite—without needing to change much of your code.
✅ Consistent API
Same code style regardless of which database you use.
✅ Prepared Statements
Helps prevent SQL injection via bound parameters:
$stmt = $pdo->prepare("SELECT * FROM users WHERE id = :id");
$stmt->execute(['id' => $userId]);✅ Transactions Support
Great for use cases like banking systems or other operations that need rollback/commit.
✅ Exception-based Error Handling
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);✅ Easy Database Switching
Switching from MySQL to PostgreSQL? Usually only the DSN and driver need to be changed.
$dsn = 'mysql:host=localhost;dbname=testdb;charset=utf8mb4';
$user = 'root';
$pass = '';
try {
$pdo = new PDO($dsn, $user, $pass);
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
echo "Connected successfully!";
} catch (PDOException $e) {
echo "Connection failed: " . $e->getMessage();
}PDO is the recommended way to work with databases in modern PHP applications—especially for its security, flexibility, and ease of use.
Transaction Control Language (TCL) is a subset of SQL used to manage transactions in a database. A transaction is a logical unit of work that may consist of one or more SQL statements—typically INSERT, UPDATE, or DELETE—that should be executed together.
TCL provides commands to ensure that transactions are properly completed or rolled back in case of errors.
| Command | Description |
|---|---|
COMMIT |
Saves all changes made in the current transaction permanently to the database. |
ROLLBACK |
Undoes all changes made since the last COMMIT. |
SAVEPOINT |
Creates a named point within a transaction that you can roll back to later. |
ROLLBACK TO SAVEPOINT |
Reverts changes back to a specific savepoint. |
SET TRANSACTION |
Defines characteristics for the current transaction (e.g., isolation level). |
BEGIN;
UPDATE account SET balance = balance - 100 WHERE account_id = 1;
UPDATE account SET balance = balance + 100 WHERE account_id = 2;
COMMIT;→ Both updates are completed together. If an error occurs, you could use ROLLBACK to cancel both operations.
TCL commands only work in database systems that support transactions (e.g., PostgreSQL, Oracle, or MySQL with InnoDB).
Data Control Language (DCL) is a subset of SQL that focuses on managing access rights and permissions within a database. DCL commands are used to control who can do what in the database.
| Command | Description |
|---|---|
GRANT |
Gives a user specific privileges (e.g., to read or modify data) |
REVOKE |
Removes previously granted privileges from a user |
GRANT SELECT, INSERT ON Customers TO User123;
REVOKE INSERT ON Customers FROM User123;SELECT – Read data
INSERT – Add new data
UPDATE – Modify existing data
DELETE – Remove data
ALL – Grant all available privileges
DCL handles security and access control in the database.
Typically used by a database administrator (DBA).
Permissions can be granted at the table, column, or database level.
DCL operations are often transaction-dependent, requiring a COMMIT to take effect.
DDL (Data Definition Language) – Defines the database structure (e.g., tables)
DML (Data Manipulation Language) – Works with the data itself (e.g., insert or update)
TCL (Transaction Control Language) – Manages transactions (COMMIT, ROLLBACK)
DCL (Data Control Language) – Manages permissions and user access
Data Manipulation Language (DML) is a subset of SQL (Structured Query Language) used to manage and manipulate data within a database. With DML, users can insert, query, update, and delete data — essentially everything you'd typically do with data stored in a database.
| Command | Purpose |
|---|---|
SELECT |
Retrieve data from a table |
INSERT |
Add new data |
UPDATE |
Modify existing data |
DELETE |
Remove data |
-- Insert
INSERT INTO customers (name, city) VALUES ('Müller', 'Berlin');
-- Query
SELECT * FROM customers WHERE city = 'Berlin';
-- Update
UPDATE customers SET city = 'Hamburg' WHERE name = 'Müller';
-- Delete
DELETE FROM customers WHERE name = 'Müller';DML deals with the data inside tables, not with the structure of the tables themselves (that's handled by Data Definition Language, DDL).
DML operations can often be rolled back (undone), especially when transactions are supported.
In short: DML is the toolset you use to keep your database dynamic and interactive by constantly adding, reading, modifying, or deleting data.
DQL stands for Data Query Language, and it's a subset of SQL (Structured Query Language). It is used specifically to query data from a database without modifying it.
Read-only: DQL is used to retrieve data, not to insert, update, or delete it.
The primary command used is:
SELECTExample:
SELECT name, birthdate FROM customers WHERE city = 'Berlin';This command retrieves the names and birthdates of all customers living in Berlin — without changing any data.
| Sub-language | Meaning | Main Purpose |
|---|---|---|
| DQL | Data Query Language | Reading data |
| DML | Data Manipulation Language | Inserting, updating, deleting data (INSERT, UPDATE, DELETE) |
| DDL | Data Definition Language | Defining database structure (CREATE, ALTER, DROP) |
| DCL | Data Control Language | Managing access rights (GRANT, REVOKE) |
| TCL | Transaction Control Language | Handling transactions (COMMIT, ROLLBACK) |
Doctrine DBAL (Database Abstraction Layer) is a PHP library that provides an abstraction layer for database access. It is part of the Doctrine project (a popular ORM for PHP), but it can be used independently of the ORM.
Doctrine DBAL offers a unified API to interact with different databases (such as MySQL, PostgreSQL, SQLite, etc.) without writing raw SQL specific to each database system.
Easily configure and manage connections to various database systems.
Supports connection pooling, transactions, and more.
Build SQL queries programmatically using an object-oriented API:
$qb = $conn->createQueryBuilder();
$qb->select('u.id', 'u.name')
->from('users', 'u')
->where('u.age > :age')
->setParameter('age', 18);
$stmt = $qb->executeQuery();Database Independence
The same code works with different database systems (e.g., MySQL, PostgreSQL) with minimal changes.
Schema Management
Tools to create, update, and compare database schemas.
Useful for migrations and automation.
Data Type Conversion
Automatically converts data between PHP types and database-native types.
use Doctrine\DBAL\DriverManager;
$conn = DriverManager::getConnection([
'dbname' => 'test',
'user' => 'root',
'password' => '',
'host' => 'localhost',
'driver' => 'pdo_mysql',
]);
$result = $conn->fetchAllAssociative('SELECT * FROM users');You might choose DBAL without ORM if:
You want full control over your SQL.
Your project doesn't need complex object-relational mapping.
You're working with a legacy database or custom queries.
Doctrine DBAL is a powerful tool for clean, portable, and secure database access in PHP. It sits between raw PDO usage and a full-featured ORM like Doctrine ORM, making it ideal for developers who want abstraction and flexibility without the overhead of ORM logic.
Memcached is a distributed in-memory caching system commonly used to speed up web applications. It temporarily stores frequently requested data in RAM to avoid expensive database queries or API calls.
Key-Value Store: Data is stored as key-value pairs.
In-Memory: Runs entirely in RAM, making it extremely fast.
Distributed: Supports multiple servers (clusters) to distribute load.
Simple API: Provides basic operations like set, get, and delete.
Eviction Policy: Uses LRU (Least Recently Used) to remove old data when memory is full.
Caching Database Queries: Reduces load on databases like MySQL or PostgreSQL.
Session Management: Stores user sessions in scalable web applications.
Temporary Data Storage: Useful for API rate limiting or short-lived data caching.
Memcached: Faster for simple key-value caching, scales well horizontally.
Redis: Offers more features like persistence, lists, hashes, sets, and pub/sub messaging.
sudo apt update && sudo apt install memcached
sudo systemctl start memcachedIt can be used with PHP or Python via appropriate libraries.
Beego is an open-source web framework written in programming language Go (Golang). It is widely used for building scalable web applications and APIs. Beego provides a comprehensive platform for developers to create both simple and complex applications quickly and efficiently.
Modular Design:
Built-in Web Server:
MVC Architecture:
Automatic Routing:
Integrated ORM:
Task Scheduler:
RESTful API Support:
Logging and Configuration:
If you're considering using Beego, it's worth evaluating your project requirements and comparing it with alternative frameworks such as Gin, Echo, or Fiber to determine the best fit.
Strapi is a headless CMS (Content Management System) built with JavaScript, designed specifically for developers. It offers a flexible and open solution for managing content and APIs. Here's an overview of Strapi's key features:
Midjourney
