从解释结果改进查询答案

【问题标题】：Improve a query from Explain results从解释结果改进查询
【发布时间】：2020-07-01 01:52:10
【问题描述】：

我有一个根据搜索条件动态组合的复杂查询。但是，以最简单的形式，它仍然非常慢。它运行的主表有大约 1000 万条记录。我对“基本”查询进行了解释，解释的第一行看起来很糟糕（至少对于像我这样的新手 dba 而言）。我已经阅读了一些关于 EXPLAIN 的教程，但我仍然不确定如何修复查询。所以，结果的第一行似乎表明了问题，但我不知道该怎么办。即使我愿意，我也无法制作那么长的复合键，并且该 possible_keys 列中的某些字段名称甚至不在患者表中。任何帮助将不胜感激。

   id,select_type,table,type,possible_keys,key,key_len,ref,rows,Extra
1,SIMPLE,patients,range,"PRIMARY,location,appt_date,status,radiologist,contract,lastname,paperwork,images_archived,hash,created,document_attached,all_images_archived,last_image_archived,modality,study_uid,company,second_access,firstname,report_delivered,ssn,order_entry_status,dob,tech,doctor,mobile_facility,accession,location_appt_date,location_created,location_lastname,ref,person_seq",location_appt_date,55,NULL,573534,"Using index condition; Using where; Using temporary; Using filesort"
1,SIMPLE,receivable_transactions,ref,patient_seq,patient_seq,4,ris-dev.patients.seq,1,NULL
1,SIMPLE,patients_dispatch,ref,patient_seq,patient_seq,4,ris-dev.patients.seq,1,NULL
1,SIMPLE,mobile_facility,ref,"unique_index,name,location",unique_index,115,"ris-dev.patients.mobile_facility,const",1,"Using where"
1,SIMPLE,mobile_facility_service_areas,eq_ref,PRIMARY,PRIMARY,4,ris-dev.mobile_facility.service_area,1,NULL

编辑：相同的解释，但重新格式化以更易于阅读：

id select_type table                         type   possible_keys        key                key_len ref                                    rows   Extra

1  SIMPLE      patients                      range  PRIMARY              location_appt_date 55      NULL                                   573534 Using index condition; Using where; Using temporary; Using filesort
                                                    location
                                                    appt_date
                                                    status
                                                    radiologist
                                                    contract
                                                    lastname
                                                    paperwork
                                                    images_archived
                                                    hash
                                                    created
                                                    document_attached
                                                    all_images_archived
                                                    last_image_archived
                                                    modality
                                                    study_uid
                                                    company
                                                    second_access
                                                    firstname
                                                    report_delivered
                                                    ssn 
                                                    order_entry_status
                                                    dob 
                                                    tech
                                                    doctor
                                                    mobile_facility
                                                    accession
                                                    location_appt_date
                                                    location_created
                                                    location_lastname
                                                    ref 
                                                    person_seq

1  SIMPLE      receivable_transactions       ref    patient_seq          patient_seq        4       ris-dev.patients.seq                   1      NULL
1  SIMPLE      patients_dispatch             ref    patient_seq          patient_seq        4       ris-dev.patients.seq                   1      NULL
1  SIMPLE      mobile_facility               ref    unique_index         unique_index       115     ris-dev.patients.mobile_facility,const 1      Using where
                                                    name
                                                    location
1  SIMPLE      mobile_facility_service_areas eq_ref PRIMARY              PRIMARY            4       ris-dev.mobile_facility.service_area   1      NULL

解释是针对以下查询和表结构设置的。

    SELECT patients.fax_in_queue, patients.modality, patients.stat, patients.created, patients.seq, patients.lastname, 
patients.firstname, patients.appt_date, patients.status, patients.contract, patients.location, patients.unique_hash, 
patients.images_archived, patients.report_delivered, patients.doctor, patients.mobile_facility, patients.history, 
patients.dob, patients.all_images_archived, patients.order_entry_status, patients.tech, patients.radiologist, 
patients.last_image_archived, patients.state, patients.ss_comments, patients.completed, patients.report_status, 
patients.have_paperwork, patients.facility_room_number, patients.facility_station_name, patients.facility_bed, 
patients.findings_level, patients.document_attached, patients.study_start, patients.company, patients.accession, 
patients.number_images, patients.client_number_images, patients.sex, patients.threshhold , GROUP_CONCAT(CONCAT(CONCAT(receivable_transactions.modifier, " "), 
receivable_transactions.description) SEPARATOR ", ") AS rt_desc , patients_dispatch.seq AS doc_seq, patients_dispatch.requisition_last_sent, 
patients_dispatch.requisition_signed_by_file_seq, patients_dispatch.requisition_signed, patients_dispatch.order_reason, patients_dispatch.order_comments, 
patients_dispatch.order_taken, patients_dispatch.order_tech_last_notified, patients_dispatch.order_tech_in_transit, patients_dispatch.order_tech_in, 
patients_dispatch.order_tech_out, patients_dispatch.order_tech_ack, patients_dispatch.addr1 AS d_addr1, patients_dispatch.addr2 AS d_addr2, 
patients_dispatch.city AS d_city, patients_dispatch.state AS d_state, patients_dispatch.zip AS d_zip, CONCAT(patients.status, order_tech_out, 
order_tech_in, order_tech_in_transit) as pseudo_status , mobile_facility.requisition_fax, mobile_facility.station_list, mobile_facility.address1 as mf_addr1, 
mobile_facility.address2 as mf_addr2, mobile_facility.city as mf_city, mobile_facility.state as mf_state, mobile_facility.zip as mf_zip, 
mobile_facility.phone as mf_phone, mobile_facility.phone2 as mf_phone2, mobile_facility_service_areas.name as mf_service_area 
FROM patients LEFT JOIN receivable_transactions ON patients.seq = receivable_transactions.patient_seq 
LEFT JOIN patients_dispatch ON patients.seq = patients_dispatch.patient_seq 
LEFT JOIN mobile_facility ON patients.location = mobile_facility.location AND patients.mobile_facility = mobile_facility.name 
LEFT JOIN mobile_facility_service_areas ON mobile_facility.service_area = mobile_facility_service_areas.seq 
WHERE patients.location = "XYZCompany"  AND  ((patients.appt_date >= '2020-03-19' AND patients.appt_date <= '2020-03-19 23:59:59') 
OR (patients.appt_date <= '2020-03-19' AND patients.status < 'X')) 
GROUP BY patients.seq DESC  
ORDER BY patients.status, patients.order_entry_status,  pseudo_status, patients.order_entry_status,patients.lastname);

CREATE TABLE `patients` (
  `seq` int(11) NOT NULL AUTO_INCREMENT,
  `person_seq` int(11) NOT NULL,
  `firstname` varchar(20) NOT NULL DEFAULT '',
  `lastname` varchar(30) NOT NULL DEFAULT '',
  `middlename` varchar(20) NOT NULL DEFAULT '',
  `ref` varchar(50) NOT NULL DEFAULT '',
  `location` varchar(50) NOT NULL DEFAULT '',
  `doctor` varchar(50) NOT NULL,
  `radiologist` varchar(20) NOT NULL DEFAULT '',
  `contract` varchar(50) NOT NULL,
  `history` mediumtext NOT NULL,
  `dob` varchar(15) NOT NULL DEFAULT '0000-00-00',
  `appt_date` date NOT NULL DEFAULT '0000-00-00',
  `status` tinyint(4) NOT NULL DEFAULT '0',
  `tech` varchar(50) NOT NULL DEFAULT '',
  `created` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `ss_comments` mediumtext NOT NULL,
  `mobile_facility` varchar(60) NOT NULL DEFAULT '',
  `facility_room_number` varchar(50) NOT NULL,
  `facility_bed` varchar(20) NOT NULL,
  `facility_station_name` varchar(50) NOT NULL,
  `stat` tinyint(4) NOT NULL DEFAULT '0',
  `have_paperwork` tinyint(4) NOT NULL DEFAULT '0',
  `completed` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `sex` char(1) NOT NULL DEFAULT '',
  `unique_hash` varchar(100) NOT NULL DEFAULT '',
  `number_images` int(11) NOT NULL DEFAULT '0',
  `client_number_images` int(11) NOT NULL,
  `images_archived` tinyint(4) NOT NULL DEFAULT '0',
  `completed_fax` varchar(10) NOT NULL DEFAULT '0' COMMENT 'This is the number the completed report is faxed to.',
  `report_delivered` tinyint(4) NOT NULL DEFAULT '0',
  `report_delivered_time` datetime NOT NULL,
  `document_attached` tinyint(4) NOT NULL DEFAULT '0',
  `modality` varchar(3) NOT NULL,
  `last_image_archived` datetime NOT NULL,
  `all_images_archived` tinyint(4) NOT NULL DEFAULT '0',
  `fax_in_queue` varchar(12) NOT NULL,
  `accession` varchar(100) NOT NULL,
  `study_uid` varchar(100) NOT NULL,
  `order_entry_status` tinyint(4) NOT NULL,
  `compare_to` varchar(15) NOT NULL,
  `state` varchar(3) NOT NULL,
  `company` int(11) NOT NULL,
  `second_access` varchar(50) NOT NULL,
  `threshhold` datetime NOT NULL,
  `report_status` tinyint(4) NOT NULL,
  `second_id` varchar(50) NOT NULL,
  `rad_alerted` tinyint(4) NOT NULL,
  `assigned` datetime NOT NULL,
  `findings_level` tinyint(4) NOT NULL,
  `report_viewed` tinyint(4) NOT NULL,
  `study_received` datetime NOT NULL,
  `study_start` datetime NOT NULL,
  `study_end` datetime NOT NULL,
  `completed_email` varchar(50) NOT NULL,
  `completed_send` varchar(255) NOT NULL,
  `ssn` varchar(12) NOT NULL,
  `exorder_number` varchar(30) NOT NULL,
  `exvisit_number` varchar(30) NOT NULL,
  `row_updated` timestamp NOT NULL ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`seq`),
  KEY `location` (`location`),
  KEY `appt_date` (`appt_date`),
  KEY `status` (`status`),
  KEY `radiologist` (`radiologist`),
  KEY `contract` (`contract`),
  KEY `lastname` (`lastname`),
  KEY `paperwork` (`have_paperwork`),
  KEY `images_archived` (`images_archived`),
  KEY `hash` (`unique_hash`),
  KEY `created` (`created`),
  KEY `document_attached` (`document_attached`),
  KEY `all_images_archived` (`all_images_archived`),
  KEY `last_image_archived` (`last_image_archived`),
  KEY `modality` (`modality`),
  KEY `study_uid` (`study_uid`),
  KEY `company` (`company`),
  KEY `second_access` (`second_access`),
  KEY `firstname` (`firstname`),
  KEY `report_delivered` (`report_delivered`),
  KEY `ssn` (`ssn`),
  KEY `order_entry_status` (`order_entry_status`),
  KEY `dob` (`dob`),
  KEY `tech` (`tech`),
  KEY `doctor` (`doctor`),
  KEY `mobile_facility` (`mobile_facility`),
  KEY `accession` (`accession`),
  KEY `location_appt_date` (`location`,`appt_date`),
  KEY `location_created` (`location`,`created`),
  KEY `location_lastname` (`location`,`lastname`),
  KEY `ref` (`ref`),
  KEY `person_seq` (`person_seq`)
) ENGINE=InnoDB AUTO_INCREMENT=10242952 DEFAULT CHARSET=latin1;

CREATE TABLE `receivable_transactions` (
  `seq` int(11) NOT NULL AUTO_INCREMENT,
  `patient_seq` int(11) NOT NULL DEFAULT '0',
  `cptcode` varchar(15) NOT NULL DEFAULT '',
  `modifier` char(2) NOT NULL DEFAULT '',
  `description` varchar(100) NOT NULL DEFAULT '',
  `amount` decimal(6,2) NOT NULL DEFAULT '0.00',
  `type` char(2) NOT NULL DEFAULT '',
  `transaction` varchar(10) NOT NULL DEFAULT '',
  `radiologist` varchar(20) NOT NULL DEFAULT '',
  `status` tinyint(4) NOT NULL DEFAULT '0',
  `completed` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `created` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `report_meta_seq` int(11) NOT NULL DEFAULT '0',
  `report_header` varchar(255) NOT NULL,
  `report_body` blob NOT NULL,
  `report_impression` mediumtext NOT NULL,
  `report_hide` tinyint(4) NOT NULL,
  `radiologist_group` varchar(50) NOT NULL,
  `addendum` int(4) NOT NULL DEFAULT '0',
  `addendum_type` varchar(20) NOT NULL,
  `peer_review` int(4) NOT NULL DEFAULT '0',
  `qa_reason` varchar(255) NOT NULL DEFAULT '',
  `qa_agree` decimal(2,1) NOT NULL DEFAULT '0.0',
  `findings` tinyint(4) NOT NULL,
  `comments` mediumtext NOT NULL,
  `company` int(11) NOT NULL,
  `row_updated` timestamp NOT NULL ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`seq`),
  KEY `patient_seq` (`patient_seq`),
  KEY `cptcode` (`cptcode`),
  KEY `transaction` (`transaction`),
  KEY `type` (`type`),
  KEY `created` (`created`),
  KEY `radiologist` (`radiologist`),
  KEY `status` (`status`),
  KEY `report_meta_seq` (`report_meta_seq`),
  KEY `Billing Check Dropdown` (`status`,`completed`),
  KEY `qa_agree` (`qa_agree`),
  KEY `peer_review` (`peer_review`),
  KEY `addendum` (`addendum`),
  KEY `company` (`company`),
  KEY `completed` (`completed`)
) ENGINE=InnoDB AUTO_INCREMENT=9380351 DEFAULT CHARSET=latin1;

CREATE TABLE `patients_dispatch` (
  `seq` int(11) NOT NULL AUTO_INCREMENT,
  `patient_seq` int(11) NOT NULL,
  `order_taken` datetime NOT NULL,
  `order_taken_by` varchar(50) NOT NULL,
  `order_person_calling` varchar(50) NOT NULL,
  `order_supervising_physician` varchar(50) NOT NULL,
  `order_trip_count` tinyint(4) NOT NULL,
  `order_trip_count_max` tinyint(4) NOT NULL,
  `order_trip_visit` tinyint(4) NOT NULL,
  `order_tech_in` datetime NOT NULL,
  `order_tech_out` datetime NOT NULL,
  `order_ssn` varchar(12) NOT NULL,
  `order_service_request_time` datetime NOT NULL,
  `order_reason` varchar(255) NOT NULL,
  `order_tech_ack` datetime NOT NULL,
  `order_tech_assigned` datetime NOT NULL,
  `order_tech_last_notified` datetime NOT NULL,
  `requisition_last_sent` datetime NOT NULL,
  `requisition_signed` datetime NOT NULL,
  `requisition_signed_by` varchar(50) NOT NULL,
  `requisition_signed_by_text` varchar(75) NOT NULL,
  `requisition_signed_by_file_seq` int(11) NOT NULL,
  `order_comments` mediumtext NOT NULL,
  `order_tech_in_transit` datetime NOT NULL,
  `fasting` tinyint(1) NOT NULL,
  `collection_time` time DEFAULT NULL,
  `addr1` varchar(100) NOT NULL,
  `addr2` varchar(100) NOT NULL,
  `city` varchar(30) NOT NULL,
  `state` varchar(3) NOT NULL,
  `zip` varchar(12) NOT NULL,
  `phone` varchar(15) NOT NULL,
  `mileage_start` int(11) NOT NULL,
  `mileage_end` int(11) NOT NULL,
  PRIMARY KEY (`seq`),
  KEY `patient_seq` (`patient_seq`)
) ENGINE=InnoDB AUTO_INCREMENT=2261091 DEFAULT CHARSET=latin1;

CREATE TABLE `mobile_facility` (
  `seq` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(60) NOT NULL,
  `location` varchar(50) DEFAULT NULL,
  `address1` varchar(50) NOT NULL,
  `address2` varchar(50) NOT NULL,
  `city` varchar(50) NOT NULL,
  `state` varchar(2) NOT NULL,
  `zip` varchar(10) NOT NULL,
  `phone` varchar(15) NOT NULL,
  `phone2` varchar(15) NOT NULL,
  `fax` varchar(110) NOT NULL,
  `rads_can_read` text NOT NULL,
  `rads_cant_read` text NOT NULL,
  `only_techs` text NOT NULL,
  `never_modalities` varchar(255) NOT NULL COMMENT 'A serialized list of modalities a facility may not use.',
  `station_list` mediumtext NOT NULL,
  `email` varchar(255) NOT NULL,
  `misc1` varchar(255) NOT NULL,
  `latitude` float NOT NULL DEFAULT '0',
  `longitude` float NOT NULL DEFAULT '0',
  `affiliation` int(11) NOT NULL COMMENT 'mobile_facility_affiliations seq',
  `branch` int(11) NOT NULL COMMENT 'mobile_facility_branches seq',
  `service_area` int(11) NOT NULL COMMENT 'mobile_facility_service_areas seq',
  `other_id` varchar(50) NOT NULL COMMENT 'Usually used for HL7',
  `facility_type` varchar(2) DEFAULT NULL,
  `no_stat` tinyint(1) NOT NULL DEFAULT '0' COMMENT 'Should the facility allow stat priority on patients?',
  `facility_notes` varchar(512) DEFAULT NULL,
  `requisition_fax` varchar(110) NOT NULL,
  `report_template` text NOT NULL,
  `all_orders_stat` tinyint(1) NOT NULL,
  `sms_notification` varchar(15) NOT NULL,
  `tat` varchar(10) NOT NULL,
  `npi` varchar(15) NOT NULL,
  `NMXR` tinyint(4) NOT NULL DEFAULT '0',
  `billing_type` varchar(10) NOT NULL,
  `salesman` varchar(75) NOT NULL,
  `created_at` datetime NOT NULL,
  `updated_at` datetime NOT NULL,
  `default_bill_to` tinyint(4) NOT NULL DEFAULT '0',
  PRIMARY KEY (`seq`),
  UNIQUE KEY `unique_index` (`name`,`location`),
  KEY `name` (`name`),
  KEY `location` (`location`)
) ENGINE=InnoDB AUTO_INCREMENT=155104 DEFAULT CHARSET=latin1;

CREATE TABLE `mobile_facility_service_areas` (
  `seq` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) NOT NULL,
  `location` varchar(50) NOT NULL,
  PRIMARY KEY (`seq`)
) ENGINE=InnoDB AUTO_INCREMENT=841 DEFAULT CHARSET=latin1;

【问题讨论】：

Bill Karwin - 我已经在这个问题上工作了半天。我研究了解释并观看了教程。我仍然需要帮助。如果您知道如何帮助我，而不是因为问题没有显示足够的研究而给我反对票；如何回答问题或指出正确的方向。
我没有投反对票。我只添加了query-optimization 标签。我还将编辑您的 EXPLAIN 格式，使其更易于阅读。
possible_keys 列中的名称是索引的名称，而不是列的名称。
我认为提出任何建议并不容易，除非您显示您尝试优化的 SQL 查询，以及查询引用的每个表的 SHOW CREATE TABLE <name> 的输出。解决方案将取决于您在表中定义的列、索引和约束，没有人能猜到这一点。帮助我们为您提供帮助！
我向比尔·卡尔文道歉。我误解了这里发生的事情。让我努力为您提供所需的信息。我认为解释响应中的第一行（达到 50 万行）就足够了。我将提供更多信息。

标签： mysql sql performance query-optimization explain

【解决方案1】：

它只使用location 上的索引，但这只会将搜索范围缩小到大约一百万行。您希望它使用索引进一步缩小appt_date。

但是，在 WHERE 子句中使用 OR 会导致问题。它无法决定如何使用索引。

这是我的建议：

删除location 上的索引，因为它与以location 作为第一列的其他索引是多余的。

将location_appt_date 上的索引替换为location_appt_date_status 上的索引。

ALTER TABLE patients
  DROP KEY location,
  DROP KEY location_appt_date,
  ADD KEY location_appt_date_status (location, appt_date, status);

重构查询以使用UNION 而不是OR：

SELECT ... (all the columns you have) ... 
FROM (
        SELECT * FROM patients USE INDEX (location_appt_date_status)
        WHERE location = 'XYZCompany' AND appt_date >= '2020-03-19' AND appt_date < '2020-03-20'
        UNION 
        SELECT * FROM patients USE INDEX (location_appt_date_status)
        WHERE location = 'XYZCompany' AND appt_date <= '2020-03-19' AND status < 'X'
) AS p
LEFT JOIN receivable_transactions FORCE INDEX (patient_seq) 
  ON p.seq = receivable_transactions.patient_seq
LEFT JOIN patients_dispatch FORCE INDEX (patient_seq) 
  ON p.seq = patients_dispatch.patient_seq
INNER JOIN mobile_facility FORCE INDEX (unique_index) 
  ON p.location = mobile_facility.location AND p.mobile_facility = mobile_facility.name
INNER JOIN mobile_facility_service_areas FORCE INDEX (PRIMARY) 
  ON mobile_facility.service_area = mobile_facility_service_areas.seq
GROUP BY p.seq 
ORDER BY p.status, p.order_entry_status, pseudo_status, p.order_entry_status, p.lastname

您可能不需要我使用的所有 USE INDEX() / FORCE INDEX() 优化器提示。我这样做是因为我正在使用空表进行测试，这可能会使优化器感到困惑。

【讨论】：

太棒了！很确定是这样做的。已经很晚了，在我结束这个问题之前我需要做更多的工作，但 90% 肯定你做到了。太感谢了！（顺便说一句 - 喜欢你的书。它就在我的书架上。大部分内容都超出了我的想象。 - 我更像是一个中间件编码器，而不是一个 dba - 但它不时地帮助了我。）再次感谢。可能会在早上结束这个问题。
那么，就我的理解而言，大部分问题是 where 子句中的“或”吗？
本博客详细讲解：percona.com/blog/2006/08/10/…
抱歉耽搁了这么久。我被转移到另一个项目一段时间。感谢大家的帮助！

【解决方案2】：

让我关注对优化影响最大的部分：

    FROM  patients AS p
    LEFT JOIN  receivable_transactions AS rt  ON p.seq = rt.patient_seq
    LEFT JOIN  patients_dispatch AS pd  ON p.seq = pd.patient_seq
    LEFT JOIN  mobile_facility AS mf  ON p.location = mf.location
      AND  p.mobile_facility AS mf = mf.name
    LEFT JOIN  mobile_facility_service_areas AS sa  ON mf.service_area = sa.seq
    WHERE  p.location = "XYZCompany"
      AND  ((p.appt_date >= '2020-03-19'
                      AND  p.appt_date <= '2020-03-19 23:59:59')
              OR  (p.appt_date <= '2020-03-19'
                      AND  p.status < 'X')
           )
    GROUP BY  p.seq DESC
    ORDER BY  p.status, p.order_entry_status, pseudo_status, p.order_entry_status,
        p.lastname);

最大的问题是OR。它通常会阻止大多数优化。通常的解决方法是将其变成UNION：

( SELECT ...
    FROM .. JOIN ..
    WHERE p.location = "XYZCompany"
      AND  p.appt_date >= '2020-03-19'
      AND  p.appt_date  < '2020-03-19' + INTERVAL 1 DAY
   ... 
)
UNION ALL
( SELECT ...
    FROM .. JOIN ..
    WHERE p.location = "XYZCompany"
      AND  p.appt_date <= '2020-03-19'
      AND  p.status < 'X'
   ... 
)

每个选择都可以从patients 上的这个复合索引中受益：

(location, appt_date, status)

< 'X' 存在问题，因为不能同时有效地使用两个范围（appt_date 和 status）。 status 的可能值是多少？如果在“X”之前只有一个值，比如“M”，那么这会更好：p.status = 'M' 再加上另一个索引：(location, status, appt_date)

SELECT lots of stuff, then GROUP BY p.seq -- 这可能会产生奇怪的结果。（搜索ONLY_FULL_GROUP_BY 进行更多讨论）。可能最好先获取patients.seq 值（因为这就是您要过滤的全部内容），然后加入其他表。这将消除GROUP BY，或者至少迫使您处理从其他每个表中获取哪一行。

range location_appt_date 55 573534 Using index condition; Using where; Using temporary; Using filesort -- 说

55 = 2+50（对于 varchar(50)）+ 3（对于日期）——两者都不是 NULL。
在55的基础上，不知是不是优化得这么好，不需要OR->UNION。
如果您想进一步了解，“使用索引条件”在内部称为 ICP（索引条件下推）。
“使用文件排序”可能是轻描淡写——可能有两种，一种用于GROUP BY，一种用于ORDER BY。 EXPLAIN FORMAT=JSON SELECT ... 会说清楚。（因此我暗示应该避免使用GROUP BY。

您有一些冗余索引（与磁盘空间无关）：INDEX(a,b), INDEX(a) --> 折腾INDEX(a)。

patients 有大量的索引。

其他表似乎有足够的索引供您查询。

【讨论】：

哦，好吧。比尔说了大部分相同的话。