MySQL explain

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 select_id The SELECT identifier
• select_type None The SELECT type
• table table_name The table for the output row
• partitions partitions The matching partitions
• type access_type The join type
• possible_keys possible_keys The possible indexes to choose
• key key The index actually chosen
• key_len key_length The length of the chosen key
• ref ref The columns compared to the index
• rows rows Estimate of rows to be examined
• filtered filtered Percentage of rows filtered by table condition
• Extra None Additional information

1. https://dev.mysql.com/doc/refman/8.0/en/explain-output.html