如何在 PostgreSQL 中查找重复记录

Question

我有一个名为 "user_links" 的 PostgreSQL 数据库 table，它目前允许以下重复字段：

year, user_id, sid, cid

唯一约束当前是第一个名为 "id" 的字段，但是我现在希望添加一个约束以确保 year、user_id、sid和 cid 都是唯一的，但我无法应用约束，因为已经存在违反此约束的重复值。

有没有办法找到所有重复项？

Answer 1

基本思路是使用带计数聚合的嵌套查询：

select * from yourTable ou
where (select count(*) from yourTable inr
where inr.sid = ou.sid) > 1

您可以调整内部查询中的 where 子句以缩小搜索范围。

评论中提到的还有另一个很好的解决方案，（但不是每个人都读过）：

select Column1, Column2, count(*)
from yourTable
group by Column1, Column2
HAVING count(*) > 1

或更短：

SELECT (yourTable.*)::text, count(*)
FROM yourTable
GROUP BY yourTable.*
HAVING count(*) > 1

Answer 2

您可以在将重复的字段上加入相同的 table，然后在 id 字段上反加入。 Select 来自第一个 table 别名 (tn1) 的 id 字段，然后在第二个 table 别名的 id 字段上使用 array_agg 函数。最后，为了使 array_agg 函数正常工作，您将按 tn1.id 字段对结果进行分组。这将生成一个结果集，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，对于一个 id，将在 duplicate_entries 数组中的 id 也会在结果集中有自己的条目。您将不得不使用此结果集来决定要将哪个 ID 作为 'truth.' 不应删除的记录的来源。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)

Selects 具有重复的 ID 的最小数量（假设 ID 正在增加 int PK）。这些将是您随身携带的 ID。

Answer 3

来自“Find duplicate rows with PostgreSQL”的智能解决方案：

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

Answer 4

为了方便起见，我假设您希望仅对列 year 应用唯一约束，并且主键是一个名为 id 的列。

为了找到重复值，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，您会得到一个 table，其中包含 table 中所有重复的年份。为了删除除了最新的重复项之外的所有重复项，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;

Answer 5

在您的情况下，由于限制，您需要删除重复的记录。

找到重复的行
按 created_at 日期组织它们 - 在这种情况下，我保留最旧的
删除带有USING的记录以过滤正确的行

WITH duplicated AS ( 
    SELECT id,
        count(*) 
    FROM products 
    GROUP BY id 
    HAVING count(*) > 1), 
ordered AS ( 
    SELECT p.id, 
        created_at, 
        rank() OVER (partition BY p.id ORDER BY p.created_at) AS rnk 
    FROM products o 
    JOIN     duplicated d ON d.id = p.id ), 
products_to_delete AS ( 
    SELECT id, 
        created_at 
    FROM   ordered 
    WHERE  rnk = 2
) 
DELETE 
FROM products 
USING products_to_delete 
WHERE products.id = products_to_delete.id 
    AND products.created_at = products_to_delete.created_at;

Answer 6

受 Sandro Wiggers 的启发，我做了一些类似于

的事情

WITH ordered AS ( 
  SELECT id,year, user_id, sid, cid,
    rank() OVER (PARTITION BY year, user_id, sid, cid ORDER BY id) AS rnk 
  FROM user_links 
), 
to_delete AS ( 
  SELECT id
  FROM   ordered 
  WHERE  rnk > 1
) 
DELETE 
FROM user_links
USING to_delete 
WHERE user_link.id = to_delete.id;

如果要测试的话，稍微改一下：

WITH ordered AS ( 
  SELECT id,year, user_id, sid, cid,
    rank() OVER (PARTITION BY year, user_id, sid, cid ORDER BY id) AS rnk 
  FROM user_links 
), 
to_delete AS ( 
  SELECT id,year,user_id,sid, cid
  FROM   ordered 
  WHERE  rnk > 1
) 
SELECT * FROM to_delete;

这将概述将要删除的内容（当运行删除，但不需要它们）

Answer 7

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;

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;

except all 也有效。由于 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;

到目前为止可以使用 null 和 non-nulls。
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 *;

如何在 PostgreSQL 中查找重复记录

How to find duplicate records in PostgreSQL

sql

postgresql

duplicates