### 8.8.1 Optimizing Queries with EXPLAIN

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 The [`EXPLAIN`](explain.html) statement provides information about how MySQL executes statements:

* [`EXPLAIN`](explain.html) works with [`SELECT`](select.html), [`DELETE`](delete.html), [`INSERT`](insert.html), [`REPLACE`](replace.html), and [`UPDATE`](update.html) statements.

* When [`EXPLAIN`](explain.html) is used with an explainable statement, MySQL displays information from the optimizer about the statement execution plan. That is, MySQL explains how it would process the statement, including information about how tables are joined and in which order. For information about using [`EXPLAIN`](explain.html) to obtain execution plan information, see [Section 8.8.2, “EXPLAIN Output Format”](explain-output.html).

* When [`EXPLAIN`](explain.html) is used with `FOR CONNECTION *`connection_id`*` rather than an explainable statement, it displays the execution plan for the statement executing in the named connection. See [Section 8.8.4, “Obtaining Execution Plan Information for a Named Connection”](explain-for-connection.html).

* For [`SELECT`](select.html) statements, [`EXPLAIN`](explain.html) produces additional execution plan information that can be displayed using [`SHOW WARNINGS`](show-warnings.html). See [Section 8.8.3, “Extended EXPLAIN Output Format”](explain-extended.html).

* [`EXPLAIN`](explain.html) is useful for examining queries involving partitioned tables. See [Section 24.3.5, “Obtaining Information About Partitions”](partitioning-info.html).

* The `FORMAT` option can be used to select the output format. `TRADITIONAL` presents the output in tabular format. This is the default if no `FORMAT` option is present. `JSON` format displays the information in JSON format.

[]() With the help of [`EXPLAIN`](explain.html), you can see where you should add indexes to tables so that the statement executes faster by using indexes to find rows. You can also use [`EXPLAIN`](explain.html) to check whether the optimizer joins the tables in an optimal order. To give a hint to the optimizer to use a join order corresponding to the order in which the tables are named in a [`SELECT`](select.html) statement, begin the statement with `SELECT STRAIGHT_JOIN` rather than just [`SELECT`](select.html). (See [Section 13.2.10, “SELECT Statement”](select.html).) However, `STRAIGHT_JOIN` may prevent indexes from being used because it disables semijoin transformations. See [Section 8.2.2.1, “Optimizing IN and EXISTS Subquery Predicates with Semijoin Transformations”](semijoins.html).

 The optimizer trace may sometimes provide information complementary to that of [`EXPLAIN`](explain.html). However, the optimizer trace format and content are subject to change between versions. For details, see [MySQL Internals: Tracing the Optimizer](https://dev.mysql.com/doc/internals/en/optimizer-tracing.html).

 If you have a problem with indexes not being used when you believe that they should be, run [`ANALYZE TABLE`](analyze-table.html) to update table statistics, such as cardinality of keys, that can affect the choices the optimizer makes. See [Section 13.7.3.1, “ANALYZE TABLE Statement”](analyze-table.html).

Note

[`EXPLAIN`](explain.html) can also be used to obtain information about the columns in a table. [`EXPLAIN *`tbl_name`*`](explain.html) is synonymous with `DESCRIBE *`tbl_name`*` and `SHOW COLUMNS FROM *`tbl_name`*`. For more information, see [Section 13.8.1, “DESCRIBE Statement”](describe.html), and [Section 13.7.7.5, “SHOW COLUMNS Statement”](show-columns.html).

