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 | April 6, 2016 |  Posted In: EXPLAIN, EXPLAIN FORMAT=JSON is cool!, JSON, MySQL


EXPLAIN FORMAT=JSON wrap-upThis blog is an EXPLAIN FORMAT=JSON wrap-up for the series of posts I’ve done in the last few months.

In this series, we’ve discussed everything unique to EXPLAIN FORMAT=JSON. I intentionally skipped a description of members such as table_name, access_type  or select_id, which are not unique.

In this series, I only mentioned in passing members that replace information from the Extra column in the regular EXPLAIN output, such as using_join_buffer , partitions, using_temporary_table  or simply message. You can see these in queries like the following:


Their use is fairly intuitive, similar to regular EXPLAIN, and I don’t think one can achieve anything from reading a blog post about each of them.

The only thing left to list is a Table of Contents for the series:

attached_condition: How EXPLAIN FORMAT=JSON can spell-check your queries

rows_examined_per_scan, rows_produced_per_join: EXPLAIN FORMAT=JSON answers on question “What number of filtered rows mean?”

used_columns: EXPLAIN FORMAT=JSON tells when you should use covered indexes

used_key_parts: EXPLAIN FORMAT=JSON provides insight into which part of multiple-column key is used

EXPLAIN FORMAT=JSON: everything about attached_subqueries, optimized_away_subqueries, materialized_from_subquery

EXPLAIN FORMAT=JSON provides insights on optimizer_switch effectiveness

EXPLAIN FORMAT=JSON: order_by_subqueries, group_by_subqueries details on subqueries in ORDER BY and GROUP BY

grouping_operation, duplicates_removal: EXPLAIN FORMAT=JSON has all details about GROUP BY

EXPLAIN FORMAT=JSON has details for subqueries in HAVING, nested selects and subqueries that update values

ordering_operation: EXPLAIN FORMAT=JSON knows everything about ORDER BY processing

EXPLAIN FORMAT=JSON knows everything about UNIONs: union_result and query_specifications

EXPLAIN FORMAT=JSON: buffer_result is not hidden!

EXPLAIN FORMAT=JSON: cost_info knows why optimizer prefers one index to another

EXPLAIN FORMAT=JSON: nested_loop makes JOIN hierarchy transparent

Thanks for following the series!

Sveta Smirnova

Sveta joined Percona in 2015. Her main professional interests are problem solving, working with tricky issues, bugs, finding patterns that can solve typical issues quicker and teaching others how to deal with MySQL issues, bugs and gotchas effectively. Before joining Percona Sveta worked as a Support Engineer in the MySQL Bugs Analysis Support Group in MySQL AB-Sun-Oracle. She is the author of the book "MySQL Troubleshooting" and JSON UDF functions for MySQL.

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