ClickHouse Estimates Join Cardinality from Distinct-Value Counts
ClickHouse’s join cost model is built from NDV counts, min/max ranges and row estimates.
Optimizer
ClickHouse Reorders Joins by Turning the Join Tree into a Graph
ClickHouse flattens the join tree into a graph, searches it for a cheaper order, and rebuilds the plan.
ClickHouse Searches Join Orders with Dynamic Programming
ClickHouse ships three DP join-order searches over a relation-set memo, with a plan budget and a fallback chain.