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
- 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