mysql 查看执行计划

mysql 可以通过 desc 和 explain 展示sql的执行计划，作用一样的。

可以使用的条件： SELECT, DELETE, INSERT, REPLACE, and UPDATE statements.

The DESCRIBE and EXPLAIN statements are synonyms. In practice, the DESCRIBE keyword is more often used to obtain information about table structure, whereas EXPLAIN is used to obtain a query execution plan (that is, an explanation of how MySQL would execute a query。

使用说明：

{EXPLAIN | DESCRIBE | DESC}
    tbl_name [col_name | wild]

{EXPLAIN | DESCRIBE | DESC}
    [explain_type]
    {explainable_stmt | FOR CONNECTION connection_id}

explain_type: {
    EXTENDED
  | PARTITIONS
  | FORMAT = format_name
}

format_name: {
    TRADITIONAL
  | JSON
}

explainable_stmt: {
    SELECT statement
  | DELETE statement
  | INSERT statement
  | REPLACE statement
  | UPDATE statement
}

参考地址：

https://dev.mysql.com/doc/refman/5.7/en/explain.html