創建一張測試表

create table poi 
(
id bigint(20) NOT NULL AUTO_INCREMENT COMMENT ‘id‘,
poi_id bigint(20) NOT NULL COMMENT ‘poi_id‘,
 PRIMARY KEY (`id`)
);

插入測試數據

insert into poi (poi_id) values (10),(10),(10),(20),(20),(30),(40);

查找重復的poi_id

poi_id=10 重復了三條，poi_id=20重復了兩條

select poi_id,count(poi_id) from
 
 poi group by poi_id having count(poi_id) > 1;

將重復的數據刪除但是要保留一條

1、查找需要刪除的數據

select * from poi where poi_id in
(
select poi_id from poi group by poi_id having count(poi_id) >1  
)
and id not in (select min(id) from poi group by poi_id having count(poi_id)>1);

分析:

在重復的poi_id集合中，保留每個重復poi_id中id最小的那條記錄

1、找出重復的POI_ID集合

poi_id in (select poi_id from poi group by poi_id having count(poi_id) >1)    表示找出重復的poi_id

2、在重復的poi_id集合中，按照poi_id分組，保留每個重復的poi_id的最小id

id not in(select min(id) from poi group by poi_id having count(poi_id)>1)  表示在重復的poi_id集合中，按照poi_id分組，保留每個重復的poi_i

2、執行刪除

如果執行將查詢到的數據作為刪除的條件，mysql會提示 “You can‘t specify target table ‘poi‘ for update in FROM clause”

delete from poi where id in 
(
select id from poi where poi_id in
(
select poi_id from poi group by poi_id having count(poi_id) >1
)
and id not in (select min(id) from poi group by poi_id having count(poi_id)>1)
);

遇到這種情況，我們需要將子查詢條件再包一層就可以了

delete from poi where id in 
(
select id from (
select * from poi where poi_id in
(
select poi_id from poi group by poi_id having count(poi_id) >1  
)
and id not in (select min(id) from poi group by poi_id having count(poi_id)>1)
) a
);

Mysql重復數據去重保留一條數據