Does ClickHouse Use PRIMARY KEY for Ordering When ORDER BY Is Not Defined?

In ClickHouse, the primary key serves as the default ordering mechanism when an ORDER BY clause is not explicitly defined during table creation. The primary key always acts as a prefix of the ORDER BY key, which determines how data is stored on disk for efficient read and aggregation operations. Understanding this relationship between PRIMARY KEY and ORDER BY is crucial for designing efficient ClickHouse tables, as it impacts data organization, indexing, and overall query performance.