EXPLAIN FORMAT=JSON

MariaDB starting with 10.1.2

Starting from version 10.1.2, MariaDB supports the EXPLAIN FORMAT=JSON syntax.

Synopsis

EXPLAIN FORMAT=JSON is a variant of EXPLAIN command that produces output in JSON form. The output always has one row which has only one column titled "JSON". The contents are a JSON representation of the query plan, formatted for readability:

EXPLAIN FORMAT=JSON SELECT * FROM t1 WHERE col1=1\G
*************************** 1. row ***************************
EXPLAIN: {
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t1",
      "access_type": "ALL",
      "rows": 1000,
      "filtered": 100,
      "attached_condition": "(t1.col1 = 1)"
    }
  }
}

Output is different from MySQL

The output of MariaDB's EXPLAIN FORMAT=JSON is different from EXPLAIN FORMAT=JSON in MySQL.The reasons for that are:

  • MySQL's output has deficiencies. Some are listed here: EXPLAIN FORMAT=JSON in MySQL)
  • The output of MySQL's EXPLAIN FORMAT=JSON is not defined. Even MySQL Workbench has trouble parsing it (see this blog post).
  • MariaDB has query optimizations that MySQL does not have. Ergo, MariaDB generates query plans that MySQL does not generate.

A (as yet incomplete) list of how MariaDB's output is different from MySQL can be found here: EXPLAIN FORMAT=JSON differences from MySQL.

Output format

TODO: MariaDB's output format description.

See also

  • ANALYZE FORMAT=JSON produces output like EXPLAIN FORMAT=JSON, but amended with the data from query execution.

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