mysql explain

office documentation

explain query SQL; 
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE table_name NULL ALL NULL NULL NULL NULL 1 100.00 NULL

EXPLAIN output column

Column JSON Name Meaning
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

mysql locking reads

SELECT ... FOR SHARE
SELECT ... FOR UPDATE