begin;
create table user_links(id serial,year bigint, user_id bigint, sid bigint, cid bigint);
insert into  user_links(year, user_id, sid, cid) values (null,null,null,null),
 (null,null,null,null), (null,null,null,null),
 (1,2,3,4), (1,2,3,4),
 (1,2,3,4),(1,1,3,8),
 (1,1,3,9),
 (1,null,null,null),(1,null,null,null);
commit;

使用distinct和except设置操作。

(select id, year, user_id, sid, cid from user_links order by 1)
except
select distinct on (year, user_id, sid, cid) id, year, user_id, sid, cid 
from user_links order by 1;

除了所有工作。因为id serial使所有行都是唯一的。

(select id, year, user_id, sid, cid from user_links order by 1) 
except all
select distinct on (year, user_id, sid, cid)
id, year, user_id, sid, cid  from user_links order by 1;

到目前为止适用于空值和非空值。 删除:

with a as(
(select id, year, user_id, sid, cid from user_links order by 1)
except all
select distinct on (year, user_id, sid, cid)
id, year, user_id, sid, cid  from user_links order by 1)
delete from user_links using a  where user_links.id = a.id returning *;

您可以在将被复制的字段上连接到同一个表，然后在id字段上反连接。从第一个表别名(tn1)中选择id字段，然后对第二个表别名的id字段使用array_agg函数。最后，为了使array_agg函数正常工作，您将根据tn1对结果进行分组。id字段。这将产生一个结果集，其中包含记录的id和符合连接条件的所有id的数组。

select tn1.id,
       array_agg(tn2.id) as duplicate_entries, 
from table_name tn1 join table_name tn2 on 
    tn1.year = tn2.year 
    and tn1.sid = tn2.sid 
    and tn1.user_id = tn2.user_id 
    and tn1.cid = tn2.cid
    and tn1.id <> tn2.id
group by tn1.id;

显然，在duplicate_entries数组中的id在结果集中也有自己的条目。你必须使用这个结果集来决定你想要哪个id成为“真相”的来源。唯一不应该被删除的记录。也许你可以这样做:

with dupe_set as (
select tn1.id,
       array_agg(tn2.id) as duplicate_entries, 
from table_name tn1 join table_name tn2 on 
    tn1.year = tn2.year 
    and tn1.sid = tn2.sid 
    and tn1.user_id = tn2.user_id 
    and tn1.cid = tn2.cid
    and tn1.id <> tn2.id
group by tn1.id
order by tn1.id asc)
select ds.id from dupe_set ds where not exists 
 (select de from unnest(ds.duplicate_entries) as de where de < ds.id)

选择具有重复的最小数字ID(假设ID在PK中递增)。这些就是你要保存的ID。

为了方便起见，我假设您希望仅对列year应用唯一约束，并且主键是名为id的列。

为了找到重复的值，您应该运行，

SELECT year, COUNT(id)
FROM YOUR_TABLE
GROUP BY year
HAVING COUNT(id) > 1
ORDER BY COUNT(id);

使用上面的sql语句，您将得到一个包含表中所有重复年份的表。为了删除除最新重复条目外的所有重复条目，您应该使用上面的sql语句。

DELETE
FROM YOUR_TABLE A USING YOUR_TABLE_AGAIN B
WHERE A.year=B.year AND A.id<B.id;

遵循SQL语法可以在检查重复行的时候提供更好的性能。

SELECT id, count(id)
FROM table1
GROUP BY id
HAVING count(id) > 1

begin;
create table user_links(id serial,year bigint, user_id bigint, sid bigint, cid bigint);
insert into  user_links(year, user_id, sid, cid) values (null,null,null,null),
 (null,null,null,null), (null,null,null,null),
 (1,2,3,4), (1,2,3,4),
 (1,2,3,4),(1,1,3,8),
 (1,1,3,9),
 (1,null,null,null),(1,null,null,null);
commit;

使用distinct和except设置操作。

(select id, year, user_id, sid, cid from user_links order by 1)
except
select distinct on (year, user_id, sid, cid) id, year, user_id, sid, cid 
from user_links order by 1;

除了所有工作。因为id serial使所有行都是唯一的。

(select id, year, user_id, sid, cid from user_links order by 1) 
except all
select distinct on (year, user_id, sid, cid)
id, year, user_id, sid, cid  from user_links order by 1;

到目前为止适用于空值和非空值。 删除:

with a as(
(select id, year, user_id, sid, cid from user_links order by 1)
except all
select distinct on (year, user_id, sid, cid)
id, year, user_id, sid, cid  from user_links order by 1)
delete from user_links using a  where user_links.id = a.id returning *;

从“用PostgreSQL查找重复行”这里有一个聪明的解决方案:

select * from (
  SELECT id,
  ROW_NUMBER() OVER(PARTITION BY column1, column2 ORDER BY id asc) AS Row
  FROM tbl
) dups
where 
dups.Row > 1