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EXPLAIN

TL;DR

EXPLAIN shows how ClickHouse executes a query, including which indices are used, how many rows are read, and the execution plan. Use EXPLAIN to identify optimization opportunities, verify that sorting keys and data skipping indices are being used, and understand query performance characteristics before running the actual query.

EXPLAIN shows how ClickHouse plans to execute your query, helping you identify bottlenecks and optimization opportunities.

Basic EXPLAIN Usage

Syntax:

EXPLAIN [TYPE] SELECT ...

Types:

PreviousSorting Key and Index Granularity
NextData Skipping Indices

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EXPLAIN | ClickHouse for Developers