查看“︁MySQL explain”︁的源代码

= Explain =
Explain用来查看执行计划。可用于<span class="article-label">SELECT</span>, <span class="article-label">DELETE</span>, <span class="article-label">INSERT</span>, <span class="article-label">REPLACE</span>, and <span class="article-label">UPDATE</span> statements

== 例子 ==
<pre>
mysql> explain SELECT COUNT(*) FROM vehicle_prod WHERE fin LIKE '%00000' \G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: vehicle_prod
   partitions: NULL
         type: index
possible_keys: NULL
          key: idx_vehicle_prod_fin
      key_len: 203
          ref: NULL
         rows: 3182812
     filtered: 11.11
        Extra: Using where; Using index
1 row in set, 1 warning (0.00 sec)
</pre>

其中：
;id:The SELECT identifier
;select_type:The SELECT type
*SIMPLE:Simple SELECT (not using UNION or subqueries)
*PRIMARY:Outermost SELECT
*UNION:Second or later SELECT statement in a UNION
*SUBQUERY:First SELECT in subquery
* ...
;table:The table for the output row
;partitions:The matching partitions
;type:The join type
;possible_keys:The possible indexes to choose
;key:The index actually chosen
;key_len:The length of the chosen key
;ref:The columns compared to the index
;rows:Estimate of rows to be examined
;filtered:Percentage of rows filtered by table condition
;Extra:Additional information


#https://dev.mysql.com/doc/refman/8.0/en/explain-output.html
[[Category:Database]]