mysql> set optimizer_switch='mrr=on,mrr_cost_based=on,batched_key_access=on';
1231 - Variable 'optimizer_switch' can't be set to the value of 'mrr=on,mrr_cost_based=on,batched_key_access=on'
mysql>
费曼乐园的博客例如,查询SELECT * FROM t1 WHERE (SELECT a FROM t2 WHERE t2.a=t1.a) > 0可以重写为SELECT t1.* FROM t1 LEFT ...在以前,如果派生表被物化但没有合并,MySQL会将整个表进行物化,然后使用WHERE条件对行进行筛选。