执行计划官方文档：https://dev.mysql.com/doc/refman/5.7/en/explain.html

‘

Explain 语法如下（MySQL5.7为例）：’

{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
}

　

 

一般我们都不会用到这么多参数，都是直接expain + SQL 语句，看输出的结果

输出结果一般有如下几列

 

Table 8.1 EXPLAIN Output Columns

 

Column	JSON Name	Meaning	中文描述
id	select_id	The SELECT identifier	执行计划的 标识符
select_type	None	The SELECT type	查询的类型
table	table_name	The table for the output row	输出结果集的表
partitions	partitions	The matching partitions	匹配的分区
type	access_type	The join type	表连接类型
possible_keys	possible_keys	The possible indexes to choose	查询时可能使用的索引
key	key	The index actually chosen	实际使用的索引
key_len	key_length	The length of the chosen key	索引字段的长度
ref	ref	The columns compared to the index	进行比较的索引列
rows	rows	Estimate of rows to be examined	优化器预估的记录数量
filtered	filtered	Percentage of rows filtered by table condition	根据条件过滤得到的记录的百分比
Extra	None	Additional information	额外的显示选项