Mysql ORDER BY DESC 降序排列 索引無效分析

業務場景：Mysql版本5.7.22，查詢設備生產的指定狀態最新在制品，tt_wo_wip（引擎InnoDB）735951條數據，equip_id為32e4537e59404a589b7f1ec4a55ab69b大概由162675條

• 無索引：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：創建索引

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沒有索引為什么這么快
• equip_id不存在耗時較長原因分析

減少參數一 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;

減少參數二

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;

減少參數三

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;

減少參數+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;

分析結果：列使用不等於不一定影響其他列使用索引；ORDER BY降序想使用索引需要查詢條件都是索引列