EXPLAIN query

EXPLAIN types

EXPLAIN AST
        SYNTAX
        PLAN indexes = 0,
             header = 0,
             description = 1,
             actions = 0,
             optimize = 1
             json = 0
        PIPELINE header = 0,
                 graph = 0,
                 compact = 1
        ESTIMATE
SELECT ...

• AST - abstract syntax tree
• SYNTAX - query text after AST-level optimizations
• PLAN - query execution plan
• PIPELINE - query execution pipeline
• ESTIMATE - https://github.com/ClickHouse/ClickHouse/pull/26131 (since 21.9)
• indexes=1 supported starting from 21.6 (https://github.com/ClickHouse/ClickHouse/pull/22352 )
• json=1 supported starting from 21.6 (https://github.com/ClickHouse/ClickHouse/pull/23082)

References

• https://clickhouse.com/docs/en/sql-reference/statements/explain/
• Nikolai Kochetov from Yandeх. EXPLAIN query in ClickHouse. slides, video
• https://github.com/ClickHouse/clickhouse-presentations/blob/master/meetup39/query-profiling.pdf
• https://github.com/ClickHouse/ClickHouse/issues/28847