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