Link to the original text : https://blog.csdn.net/Ax0592/article/details/122623533
https://blog.csdn.net/jj89929665/article/details/124178040
delete from tbl where id not in
(
select a.id from
(
select id from table group by column1, column2 having
count(column1) > 1 and count(column2) >1
) a
)
1.（ Wrong operation ） Check all duplicate data
Obviously, the following code runs very slowly
select * from surface t where (select count(*) from surface where Field 1=t. Field 1 AND Field 2=t. Field 2)>1
1
So we use the following grouping
1.( Speed optimization ) Check all duplicate data
SELECT *
FROM surface
WHERE ( Field 1, Field 2, Field 3) IN (SELECT Field 1, Field 2, Field 3 FROM surface
GROUP BY Field 1, Field 2, Field 3 HAVING COUNT(*) > 1)
ORDER BY Sort field
1
2
3
4
5
2. Find duplicate data
SELECT id, Field 1, Field 2, Field 3
FROM surface
WHERE id
IN (SELECT MIN(id) FROM surface GROUP BY Field 1, Field 2, Field 3 HAVING COUNT(*) > 1)
1
2
3
4
3. Filter （ Field 1, Field 2, Field 3） All duplicate the same data , Only one bar is shown （id Minimum or maximum, etc ） data , Contains data that is not duplicated （ It is recommended to use ）
SELECT *
FROM surface
WHERE id
IN (SELECT MIN(id) FROM surface GROUP BY Field 1, Field 2, Field 3)
1
2
3
4
4. Get 2 The results can be deleted through a single or multiple entries
