从没有唯一键的表中删除重复行 [英] Delete duplicate rows from table with no unique key
问题描述
如何删除 Postgres 9 表中的重复行,这些行在每个字段上都是完全重复的,并且没有可以用作唯一键的单个字段,所以我不能只是 GROUP BY
列并使用 NOT IN
语句.
How do I delete duplicates rows in Postgres 9 table, the rows are completely duplicates on every field AND there is no individual field that could be used as a unique key so I cant just GROUP BY
columns and use a NOT IN
statement.
我正在寻找单个 SQL 语句,而不是需要我创建临时表并将记录插入其中的解决方案.我知道如何做到这一点,但需要做更多的工作才能适应我的自动化流程.
I'm looking for a single SQL statement, not a solution that requires me to create temporary table and insert records into that. I know how to do that but requires more work to fit into my automated process.
表定义:
jthinksearch=> d releases_labels;
Unlogged table "discogs.releases_labels"
Column | Type | Modifiers
------------+---------+-----------
label | text |
release_id | integer |
catno | text |
Indexes:
"releases_labels_catno_idx" btree (catno)
"releases_labels_name_idx" btree (label)
Foreign-key constraints:
"foreign_did" FOREIGN KEY (release_id) REFERENCES release(id)
样本数据:
jthinksearch=> select * from releases_labels where release_id=6155;
label | release_id | catno
--------------+------------+------------
Warp Records | 6155 | WAP 39 CDR
Warp Records | 6155 | WAP 39 CDR
推荐答案
如果你有能力重写整个表,这可能是最简单的方法:
If you can afford to rewrite the whole table, this is probably the simplest approach:
WITH Deleted AS (
DELETE FROM discogs.releases_labels
RETURNING *
)
INSERT INTO discogs.releases_labels
SELECT DISTINCT * FROM Deleted
如果您需要专门针对重复记录,您可以使用内部 ctid
字段,该字段唯一标识一行:
If you need to specifically target the duplicated records, you can make use of the internal ctid
field, which uniquely identifies a row:
DELETE FROM discogs.releases_labels
WHERE ctid NOT IN (
SELECT MIN(ctid)
FROM discogs.releases_labels
GROUP BY label, release_id, catno
)
小心ctid
;它随着时间的推移而变化.但是您可以依靠它在单个语句的范围内保持不变.
Be very careful with ctid
; it changes over time. But you can rely on it staying the same within the scope of a single statement.
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