索引下推
Block Nested-Loop and Batched Key Access Joins
BNL
开启bka
SET optimizer_switch='mrr=on,mrr_cost_based=off,batched_key_access=on';
Multi-Range Read Optimization
condition filter (目的是更准确的选择前导表)
Engine Condition Pushdown Optimization
Hash Join Optimization(无索引,等值连接)
Beginning with MySQL 8.0.18, MySQL employs a hash join for any query for which each join has an equi-join condition and uses no indexes