What is the difference between PostgreSQL and ClickHouse? When should you use each of them?

PostgreSQL and ClickHouse are different types of database management systems optimized for different tasks.

PostgreSQL:

• General-purpose relational DBMS.
• Supports transactions, complex queries, indexes, foreign keys.
• Well-suited for OLTP (online transaction processing).
• Used when data integrity and complex business logic are important.

ClickHouse:

• Column-oriented analytical DBMS.
• Optimized for very fast analytical queries on large volumes of data.
• Suitable for OLAP (online analytical processing).
• Used for collecting and analyzing logs, metrics, large data streams.

When to use:

• If a classic relational database with transactions and complex relationships is needed — PostgreSQL.
• If high-speed analytics on large data volumes are required — ClickHouse.

Example: an online store can store orders and users in PostgreSQL, and use ClickHouse for analyzing sales and customer behavior.