PostgreSQL vs MySQL - So sánh toàn diện¶

Tổng quan¶

Tiêu chí	PostgreSQL	MySQL
Loại	Object-Relational Database	Relational Database
Năm ra mắt	1996	1995
License	PostgreSQL License (MIT-style)	GPL v2 / Commercial
Công ty phát triển	PostgreSQL Global Development Group	Oracle Corporation
Slogan	"The World's Most Advanced Open Source Database"	"The World's Most Popular Open Source Database"

So sánh nhanh¶

Điểm mạnh PostgreSQL¶

SQL compliance tuyệt đối
Tính năng advanced (JSON, Arrays, Custom Types)
Extensibility mạnh mẽ
MVCC hiệu quả
Data integrity cao
Complex queries performance

Điểm mạnh MySQL¶

Performance cao cho simple queries
Replication dễ setup
Ecosystem phong phú
Memory usage thấp
Easy to learn & deploy
Wide hosting support

Kiến trúc & Tính năng¶

PostgreSQL¶

┌─────────────────────────────────────┐
│           PostgreSQL                │
├─────────────────────────────────────┤
│ • Object-Relational Model           │
│ • Single Storage Engine             │
│ • MVCC (Multi-Version Concurrency)  │
│ • Write-Ahead Logging (WAL)         │
│ • Extensible Architecture           │
└─────────────────────────────────────┘

Tính năng đặc biệt:

JSON/JSONB: Native JSON support với indexing
Arrays: Lưu trữ mảng trong single column
Custom Types: Tạo data types riêng
Inheritance: Table inheritance
Extensions: PostGIS, pg_trgm, etc.
Window Functions: Advanced analytics
CTEs: Common Table Expressions

MySQL¶

┌─────────────────────────────────────┐
│             MySQL                   │
├─────────────────────────────────────┤
│ • Pure Relational Model             │
│ • Multiple Storage Engines:         │
│   - InnoDB (default, ACID)          │
│   - MyISAM (fast, no transactions)  │
│   - Memory (RAM-based)              │
│   - Archive (compressed)            │
└─────────────────────────────────────┘

Tính năng đặc biệt:

Storage Engines: Linh hoạt cho từng use case
Query Cache: Built-in query result caching
Partitioning: Table partitioning native
Replication: Master-slave, master-master
Cluster: MySQL Cluster (NDB)

Performance Benchmark¶

PostgreSQL thắng khi:¶

Complex Joins: 2-3x faster với multi-table joins
Analytical Queries: Window functions, aggregations
Concurrent Writes: MVCC handles better
Large Datasets: Better optimizer cho big data
JSON Operations: Native JSONB indexing

MySQL thắng khi:¶

Simple SELECTs: 20-30% faster cho basic queries
INSERT/UPDATE Heavy: Optimized cho high-volume writes
Read Replicas: Faster replication lag
Memory Usage: Lower memory footprint
Connection Handling: Better với nhiều connections

Use Cases & Khi nào dùng¶

Chọn PostgreSQL khi:¶

Enterprise Applications¶

Banking & Financial Systems:

Cần transaction ACID nghiêm ngặt để đảm bảo tính toán chính xác
Audit trail và compliance requirements
Complex financial calculations với custom functions
Multi-currency support với precise decimal arithmetic
Risk analysis với advanced statistical functions

Healthcare Management:

HIPAA compliance và data security
Complex patient data relationships
Medical imaging metadata (DICOM) với PostGIS
Clinical trial data với statistical analysis
Electronic Health Records với full-text search

Government Applications:

Citizen data với strict privacy requirements
GIS applications cho urban planning (PostGIS integration)
Census và demographic analysis
Tax systems với complex business rules
Document management với version control

Scientific Research:

Large dataset analysis với window functions
Time-series data cho climate/sensor monitoring
Bioinformatics với custom data types
Research publication management
Grant tracking với complex workflows

Data Warehousing:

ETL processes với parallel processing
OLAP queries với materialized views
Data lineage tracking
Complex aggregations và reporting
Integration với BI tools (Tableau, Power BI)

Technical Requirements Chi Tiết¶

ACID Compliance: Strict consistency cho financial transactions
Complex Joins: Multi-table queries với 10+ tables
JSON Workloads: Document storage với SQL querying capabilities
Full-text Search: Built-in search without external dependencies
Custom Functions: Business logic trong database layer
Advanced Indexing: GIN, GiST, BRIN indexes cho specific use cases
Concurrent Writes: High write volume với minimal locking
Data Integrity: Foreign key constraints, check constraints, triggers

Team & Budget Considerations¶

DBA Expertise: Team có kinh nghiệm với advanced SQL features
Training Investment: Budget cho PostgreSQL-specific training
Long-term Vision: Project lifecycle 3-5 years+
Data Quality Priority: Accuracy quan trọng hơn raw speed
Compliance Requirements: Regulated industries (finance, healthcare)

Chọn MySQL khi:¶

Web Applications Chi Tiết¶

E-commerce Platforms:

Product catalog với high read volume
Shopping cart sessions với fast lookups
Order processing với simple workflows
Inventory management với real-time updates
Customer reviews và ratings systems

Content Management Systems:

Blog/news sites với frequent publishing
Media galleries với metadata storage
User-generated content platforms
Comment systems với threaded discussions
SEO-friendly URL structures

Social Media Applications:

User profiles với simple relationships
Activity feeds với chronological ordering
Message systems với fast delivery
Photo/video metadata storage
Like/follow counters với high update frequency

SaaS Applications:

Multi-tenant architecture với schema isolation
User authentication và authorization
Subscription management
Usage analytics và billing
API rate limiting data

Technical Requirements Chi Tiết¶

Read-Heavy Workloads: 80% reads, 20% writes ratio
Simple Queries: Basic CRUD operations, minimal joins
Fast Replication: Master-slave setup cho read scaling
Query Cache: Repeated query optimization
Connection Pooling: Handle nhiều concurrent users
Partitioning: Table partitioning cho large datasets
Storage Engines: InnoDB cho ACID, MyISAM cho speed

Team & Budget Considerations¶

Junior-Friendly: Easier learning curve cho new developers
Rapid Development: Quick prototyping và MVP development
Shared Hosting: Wide availability trên hosting providers
Community Support: Large ecosystem của plugins/tools
Cost-Effective: Lower operational overhead

Setup & Maintenance¶

PostgreSQL Configuration¶

# Ubuntu/Debian
sudo apt install postgresql postgresql-contrib

# Basic tuning
shared_buffers = 256MB
work_mem = 4MB
maintenance_work_mem = 64MB
wal_buffers = 16MB

MySQL Configuration¶

# Ubuntu/Debian
sudo apt install mysql-server

# Basic tuning (/etc/mysql/mysql.conf.d/mysqld.cnf)
innodb_buffer_pool_size = 256M
query_cache_size = 64M
max_connections = 100

Cost Analysis¶

Factor	PostgreSQL	MySQL
License	Free (MIT-style)	Free (GPL) / Paid (Commercial)
Hosting	Moderate cost	Lower cost (widely supported)
DBA Expertise	Higher salary	Moderate salary
Training	More complex	Easier learning curve
Enterprise Support	EnterpriseDB, 2ndQuadrant	Oracle MySQL Enterprise

Migration Considerations¶

MySQL → PostgreSQL Migration¶

Data Type Mapping Challenges¶

-- MySQL Types → PostgreSQL Equivalent
TINYINT         → SMALLINT hoặc BOOLEAN
MEDIUMINT       → INTEGER  
BIGINT UNSIGNED → NUMERIC(20,0)
VARCHAR(255)    → VARCHAR(255) hoặc TEXT
ENUM('a','b')   → CHECK constraint hoặc custom type
SET('x','y')    → Array type hoặc separate table
TIMESTAMP       → TIMESTAMPTZ (với timezone)

Syntax Differences¶

-- AUTO_INCREMENT → SERIAL
-- MySQL:
CREATE TABLE users (id INT AUTO_INCREMENT PRIMARY KEY);
-- PostgreSQL:
CREATE TABLE users (id SERIAL PRIMARY KEY);

-- LIMIT syntax
-- MySQL:
SELECT * FROM users LIMIT 10, 20;  -- Offset 10, Limit 20
-- PostgreSQL:
SELECT * FROM users LIMIT 20 OFFSET 10;

-- String concatenation
-- MySQL:
SELECT CONCAT(first_name, ' ', last_name) FROM users;
-- PostgreSQL:
SELECT first_name || ' ' || last_name FROM users;

-- Case sensitivity
-- MySQL: Case-insensitive by default
-- PostgreSQL: Case-sensitive, cần ILIKE cho insensitive search

Function Differences¶

-- Date functions
-- MySQL:
SELECT NOW(), DATE_ADD(NOW(), INTERVAL 1 DAY);
-- PostgreSQL:
SELECT NOW(), NOW() + INTERVAL '1 day';

-- String functions
-- MySQL:
SELECT SUBSTRING(name, 1, 5), LENGTH(name);
-- PostgreSQL:
SELECT SUBSTR(name, 1, 5), CHAR_LENGTH(name);

-- Conditional logic
-- MySQL:
SELECT IF(age > 18, 'adult', 'minor') FROM users;
-- PostgreSQL:
SELECT CASE WHEN age > 18 THEN 'adult' ELSE 'minor' END FROM users;

Migration Tools & Process¶

pgloader: Automated migration tool

pgloader mysql://user:pass@localhost/mydb postgresql://user:pass@localhost/mydb

Schema Conversion: Manual review required for:
Stored procedures (MySQL → PL/pgSQL)
Triggers syntax differences
Index types và naming conventions
Constraints definitions
Testing Strategy:
Unit test cho each converted function
Performance testing với production-like data
Data integrity verification
Application integration testing

Gotchas & Common Issues¶

NULL handling: MySQL's relaxed NULL vs PostgreSQL's strict
Empty strings: MySQL treats '' as NULL trong numeric contexts
Date zeroes: '0000-00-00' invalid trong PostgreSQL
Group BY: PostgreSQL requires all non-aggregate columns
Backticks: MySQL table → PostgreSQL "table"
Double quotes: MySQL "string" → PostgreSQL 'string'

PostgreSQL → MySQL Migration¶

Feature Loss Considerations¶

-- Advanced features không có trong MySQL:
- Arrays: Phải normalize thành separate tables
- Custom types: Convert thành standard types
- Inheritance: Flatten thành single tables  
- Window functions: Rewrite using subqueries (MySQL < 8.0)
- JSONB: Downgrade thành JSON (performance loss)
- Full-text search: Migrate sang external solution (Elasticsearch)

Data Type Downgrades¶

-- PostgreSQL → MySQL limitations
ARRAY           → Normalized tables hoặc delimited strings
UUID            → CHAR(36) hoặc BINARY(16)
INET/CIDR       → VARCHAR với validation
JSONB           → JSON (slower, no indexing)
NUMERIC(1000,2) → DECIMAL(65,2) (MySQL max precision)
INTERVAL        → INTEGER (seconds) hoặc TIME

Schema Restructuring¶

-- Table inheritance flattening
-- PostgreSQL:
CREATE TABLE animals (id SERIAL, name TEXT);
CREATE TABLE dogs (breed TEXT) INHERITS (animals);

-- MySQL equivalent:
CREATE TABLE animals (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(255),
    type ENUM('animal', 'dog'),
    breed VARCHAR(255)  -- NULL for base animals
);

Application Code Changes¶

Error handling: Different error codes và messages
Connection strings: Driver và parameter differences
ORM adjustments: Hibernate, Django ORM configuration
Backup scripts: pg_dump → mysqldump
Monitoring queries: pg_stat_* → INFORMATION_SCHEMA

Performance Considerations¶

Query optimization: Rewrite complex analytical queries
Indexing strategy: Different index types availability
Connection pooling: Adjust pool sizes cho MySQL characteristics
Memory tuning: Different buffer pool configurations

Migration Tools & Strategy¶

MySQL Workbench Migration Wizard: GUI-based tool
Custom scripts: Python/PHP scripts cho complex transformations
Staged migration:
Read replica setup
Application dual-write period
Gradual traffic migration
Rollback plan preparation

Risk Mitigation¶

Data validation: Row counts, checksums, sample data verification
Performance baseline: Before/after performance comparison
Rollback strategy: Quick restore procedure
Training plan: Team education trên MySQL differences

Kết luận & Khuyến nghị¶

Decision Matrix¶

Your Priority	Choose
Data Integrity First (Tính toàn vẹn dữ liệu)	PostgreSQL
Speed & Simplicity (Tốc độ & Đơn giản)	MySQL
Complex Analytics (Phân tích phức tạp)	PostgreSQL
Web Development (Phát triển web)	MySQL
JSON Heavy (Sử dụng nhiều JSON)	PostgreSQL
High Concurrency (Đồng thời cao)	PostgreSQL
Easy Replication (Sao chép dễ dàng)	MySQL
Budget Constrained (Ngân sách hạn chế)	MySQL

Pro Tips¶

Start Small: MySQL cho MVP, migrate to PostgreSQL khi scale
Hybrid Approach: MySQL cho transactional, PostgreSQL cho analytics
Cloud Solutions: Consider managed services (AWS RDS, Google Cloud SQL)
Future-proofing: PostgreSQL cho long-term growth potential