Book Image

MariaDB High Performance

By : Pierre Mavro
Book Image

MariaDB High Performance

By: Pierre Mavro

Overview of this book

Table of Contents (18 chapters)
MariaDB High Performance
About the Author
About the Reviewers

The explain command

The explain SQL command provides information for a specific request. Most of the time, we get a query from the slow query logs to analyze the request. The explain command won't return the classical output of the query but will provide some information concerning the related SQL query.

The explain command can only be applied on a SELECT query. UPDATE and DELETE are supported in Version 10.0.5!

Let's take a query that you can have in your slow query logs. Here is an example with a working version of MediaWiki:

MariaDB [mediawiki]> explain select page_id, page_title, page_namespace, page_is_redirect, old_id, old_text from wiki_page, wiki_revision, wiki_text where rev_id=page_latest and old_id=rev_text_id\g;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: wiki_page
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 2005