Mysql ORDER BY DESC 降序排列 索引无效分析

业务场景：Mysql版本5.7.22，查询设备生产的指定状态最新在制品，tt_wo_wip（引擎InnoDB）735951条数据，equip_id为32e4537e59404a589b7f1ec4a55ab69b大概由162675条

• 无索引：4~5s

EXPLAIN SELECT wip.pk_id FROM tt_wo_wip wip WHERE wip.equip_id = '32e4537e59404a589b7f1ec4a55ab69b' AND wip.wip_status != '10' AND wip.del_flag='0'
ORDER BY wip.finish_time DESC LIMIT 0,1;

• 里程碑：创建索引

CREATE INDEX idx_equipId_finishTime ON tt_wo_wip (equip_id,finish_time);

• equip_id存在0.02s；equip_id不存在5~6s

EXPLAIN SELECT wip.pk_id FROM tt_wo_wip wip WHERE wip.equip_id = '32e4537e59404a589b7f1ec4a55ab69b' AND wip.wip_status != '10' AND wip.del_flag='0'
ORDER BY wip.finish_time DESC LIMIT 0,1;

• equip_id存在Extra没有索引为什么这么快
• equip_id不存在耗时较长原因分析

减少参数一 equip_id存在0.02s；equip_id不存在0.3~0.4s

EXPLAIN SELECT wip.pk_id FROM tt_wo_wip wip WHERE wip.equip_id = '32e4537e59404a589b7f1ec4a55ab69b' -- AND wip.wip_status != '10' AND wip.del_flag='0'
ORDER BY wip.finish_time DESC LIMIT 0,1;

减少参数二

EXPLAIN SELECT wip.pk_id FROM tt_wo_wip wip WHERE wip.equip_id = '32e4537e59404a589b7f1ec4a55ab69b' AND wip.wip_status != '10' -- AND wip.del_flag='0'
ORDER BY wip.finish_time DESC LIMIT 0,1;

减少参数三

EXPLAIN SELECT wip.pk_id FROM tt_wo_wip wip WHERE wip.equip_id = '32e4537e59404a589b7f1ec4a55ab69b' AND wip.del_flag='0' -- AND wip.wip_status != '10'
ORDER BY wip.finish_time DESC LIMIT 0,1;

修改升序排列 equip_id存在0.02s；equip_id不存在0.2~0.3s

EXPLAIN SELECT wip.pk_id FROM tt_wo_wip wip WHERE wip.equip_id = '32e4537e59404a589b7f1ec4a55ab69b' AND wip.wip_status != '10' AND wip.del_flag='0'
ORDER BY wip.finish_time ASC LIMIT 0,1;

减少参数+修改升序排列 equip_id存在0.02s；equip_id不存在0.2~0.3s

EXPLAIN SELECT wip.pk_id FROM tt_wo_wip wip WHERE wip.equip_id = '32e4537e59404a589b7f1ec4a55ab69b' -- AND wip.wip_status != '10' AND wip.del_flag='0'
ORDER BY wip.finish_time ASC LIMIT 0,1;

分析结果：列使用不等于不一定影响其他列使用索引；ORDER BY降序想使用索引需要查询条件都是索引列