比较两个表中的多个字段时，一个表的更新缓慢

Question

The following query is timing out after 600 seconds.

update placed p
      ,Results r
  set p.position = r.position
  where p.competitor = r.competitor
    AND p.date = r.date 
    AND REPLACE(p.time,":","") = r.time; 

The structure is as follows:

'CREATE TABLE `placed` (
  `idplaced` varchar(50) DEFAULT NULL,
  `date` decimal(8,0) DEFAULT NULL,
  `time` varchar(45) DEFAULT NULL,
  `field1` varchar(45) DEFAULT NULL,
  `competitor` varchar(45) DEFAULT NULL,
  `field2` int(2) DEFAULT NULL,
  `field3` varchar(45) DEFAULT NULL,
  `field4` varchar(45) DEFAULT NULL,
  `field5` decimal(6,2) DEFAULT NULL,
  `field6` decimal(10,2) DEFAULT NULL,
  `field7` decimal(6,2) DEFAULT NULL,
  `field8` char(1) DEFAULT NULL,
  `field9` varchar(45) DEFAULT NULL,
  `position` char(4) DEFAULT NULL,
  `field10` decimal(6,2) DEFAULT NULL,
  `field11` char(1) DEFAULT NULL,
  `field12` char(1) DEFAULT NULL,
  `field13` decimal(6,2) DEFAULT NULL,
  `field14` decimal(6,2) DEFAULT NULL,
  `field15` decimal(6,2) DEFAULT NULL,
  `field16` decimal(6,2) DEFAULT NULL,
  `field17` decimal(6,2) DEFAULT NULL,
  `field18` char(1) DEFAULT NULL,
  `field19` char(20) DEFAULT NULL,
  `field20` char(1) DEFAULT NULL,
  `field21` char(5) DEFAULT NULL,
  `field22` char(5) DEFAULT NULL,
  `field23` int(11) DEFAULT NULL
   PRIMARY KEY (`idplaced`),
  UNIQUE KEY `date_time_competitor_field18_combo` (`date`,`time`,`competitor`,`field18`)
) ENGINE=InnoDB AUTO_INCREMENT=100688607 DEFAULT CHARSET=latin1;

CREATE TABLE `results` (
  `idresults` int(11) NOT NULL AUTO_INCREMENT,
  `date` char(8) DEFAULT NULL,
  `time` char(4) DEFAULT NULL,
  `field1` varchar(45) DEFAULT NULL,
  `competitor` varchar(45) DEFAULT NULL,
  `position` char(4) DEFAULT NULL,
  `field2` varchar(45) DEFAULT NULL,
  `field3` decimal(2,0) DEFAULT NULL,
  PRIMARY KEY (`idresults`)
) ENGINE=InnoDB AUTO_INCREMENT=6644 DEFAULT CHARSET=latin1;

The PLACED table has 65,000 records, the RESULTS table has 9,000 records.

I am assuming the solution involves a JOIN statement of some descript, and I have tried taking several suggestions from this site, but am simply not finding the answer I am looking for. Simply put, I would be grateful for suggestions on this. I can put up example tables / create table code if requried.

Answer 1

First of all, you'd better send us your full tables description, using

show create table

Second, you'd better use join syntax :

update placed p
  join Results r on r.competitor = p.competitor
   set p.position = r.position
 where p.date = r.date 
   AND REPLACE(p.time,":","") = r.time;

Hope this will help.

Answer 2

The index cannot be used efficiently to perform the join because of your REPLACE operation. I'd suggest creating an index with the columns in the following slightly different order:

(date, competitor, time, position)

It may also help to add this index on both tables.

It would be even better if you could modify the data in the database so that the data in the time column was stored in the same format in both tables.