2021年5月3日 (一) 11:10的版本

Explain

Explain用来查看执行计划。可用于SELECT, DELETE, INSERT, REPLACE, and UPDATE statements

例子

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)

其中：

id: The SELECT identifier
select_type: The SELECT type
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

@@ 第22行： / 第22行： @@
 其中：
-*id	select_id	The SELECT identifier
+;id:The SELECT identifier
-*select_type	None	The SELECT type
+;select_type:The SELECT type
-*table	table_name	The table for the output row
+;table:The table for the output row
-*partitions	partitions	The matching partitions
+;partitions:The matching partitions
-*type	access_type	The join type
+;type:The join type
-*possible_keys	possible_keys	The possible indexes to choose
+;possible_keys:The possible indexes to choose
-*key	key	The index actually chosen
+;key:The index actually chosen
-*key_len	key_length	The length of the chosen key
+;key_len:The length of the chosen key
-*ref	ref	The columns compared to the index
+;ref:The columns compared to the index
-*rows	rows	Estimate of rows to be examined
+;rows:Estimate of rows to be examined
-*filtered	filtered	Percentage of rows filtered by table condition
+;filtered:Percentage of rows filtered by table condition
-*Extra	None	Additional information
+;Extra:Additional information
 #https://dev.mysql.com/doc/refman/8.0/en/explain-output.html
 [[Category:Database]]