ClickHouse JOIN performance was rebuilt between 2022 and 2026. The "avoid JOINs in ClickHouse" advice from 2020 is still circulating:


"ClickHouse can't do JOINs."

"Denormalize everything."

"Only hash join is supported."

"JOINs OOM on anything bigger than RAM."


All four were accurate in 2020. None of them are accurate today.

In 2020,...