How to delete duplicates in SQL table based on multiple fields

问题

I have a table of games, which is described as follows:

+---------------+-------------+------+-----+---------+----------------+
| Field         | Type        | Null | Key | Default | Extra          |
+---------------+-------------+------+-----+---------+----------------+
| id            | int(11)     | NO   | PRI | NULL    | auto_increment |
| date          | date        | NO   |     | NULL    |                |
| time          | time        | NO   |     | NULL    |                |
| hometeam_id   | int(11)     | NO   | MUL | NULL    |                |
| awayteam_id   | int(11)     | NO   | MUL | NULL    |                |
| locationcity  | varchar(30) | NO   |     | NULL    |                |
| locationstate | varchar(20) | NO   |     | NULL    |                |
+---------------+-------------+------+-----+---------+----------------+

But each game has a duplicate entry in the table somewhere, because each game was in the schedules for two teams. Is there a sql statement I can use to look through and delete all the duplicates based on identical date, time, hometeam_id, awayteam_id, locationcity, and locationstate fields?

回答1:

You should be able to do a correlated subquery to delete the data. Find all rows that are duplicates and delete all but the one with the smallest id. For MYSQL, an inner join (functional equivalent of EXISTS) needs to be used, like so:

delete games from games inner join 
    (select  min(id) minid, date, time,
             hometeam_id, awayteam_id, locationcity, locationstate
     from games 
     group by date, time, hometeam_id, 
              awayteam_id, locationcity, locationstate
     having count(1) > 1) as duplicates
   on (duplicates.date = games.date
   and duplicates.time = games.time
   and duplicates.hometeam_id = games.hometeam_id
   and duplicates.awayteam_id = games.awayteam_id
   and duplicates.locationcity = games.locationcity
   and duplicates.locationstate = games.locationstate
   and duplicates.minid <> games.id)

To test, replace delete games from games with select * from games. Don't just run a delete on your DB :-)

回答2:

You can try such query:

DELETE FROM table_name AS t1
WHERE EXISTS (
 SELECT 1 FROM table_name AS t2 
 WHERE t2.date = t1.date 
 AND t2.time = t1.time 
 AND t2.hometeam_id = t1.hometeam_id 
 AND t2.awayteam_id = t1.awayteam_id 
 AND t2.locationcity = t1.locationcity 
 AND t2.id > t1.id )

This will leave in database only one example of each game instance which has the smallest id.

回答3:

The best thing that worked for me was to recreate the table.

CREATE TABLE newtable SELECT * FROM oldtable GROUP BY field1,field2;

You can then rename.

回答4:

To get list of duplicate entried matching two fields

select t.ID, t.field1, t.field2
from (
  select field1, field2
  from table_name
  group by field1, field2
  having count(*) > 1) x, table_name t
where x.field1 = t.field1 and x.field2 = t.field2
order by t.field1, t.field2

And to delete all the duplicate only

DELETE x 
FROM table_name x
JOIN table_name y
ON y.field1= x.field1
AND y.field2 = x.field2
AND y.id < x.id;

回答5:

select orig.id,
       dupl.id
from   games   orig, 
       games   dupl
where  orig.date   =    dupl.date
and    orig.time   =    dupl.time
and    orig.hometeam_id = dupl.hometeam_id
and    orig. awayteam_id = dupl.awayeam_id
and    orig.locationcity = dupl.locationcity
and    orig.locationstate = dupl.locationstate
and    orig.id     <    dupl.id

this should give you the duplicates; you can use it as a subquery to specify IDs to delete.

回答6:

AS long as you are not getting id (primary key) of the table in your select query and the other data is exact same you can use SELECT DISTINCT to avoid getting duplicate results.

回答7:

delete from games 
   where id not in 
   (select max(id)  from games 
    group by date, time, hometeam_id, awayteam_id, locationcity, locationstate 
    );

Workaround

select max(id)  id from games 
    group by date, time, hometeam_id, awayteam_id, locationcity, locationstate
into table temp_table;

delete from games where id in (select id from temp);

回答8:

DELETE FROM table
WHERE id = 
    (SELECT t.id
    FROM table as t
    JOIN (table as tj ON (t.date = tj.data
                          AND t.hometeam_id = tj.hometeam_id
                          AND t.awayteam_id = tj.awayteam_id
                          ...))

来源：https://stackoverflow.com/questions/6471463/how-to-delete-duplicates-in-sql-table-based-on-multiple-fields