sql - Postgres : delete rows order by without primary key

Question

我想删除最近插入的最多“n”行。

例如:

DELETE FROM users 
WHERE user_id = %s AND group_id = %s 
ORDER BY message_date DESC

我知道这是一个语法错误，在网上搜索我发现许多 stackoverflow 答案都告诉我要使用像这样的形式

DELETE FROM users 
WHERE id IN (SELECT id ....)

不幸的是，我在该表上没有主键，它们只是没有自动递增的插入。

我该怎么做？

也许我应该像这样

WITH t AS 
(
    SELECT * 
    FROM users 
    WHERE user_id = %s AND group_id = %s 
    ORDER BY message_date DESC
) 
DELETE FROM t

???

Answer 1

如果您的表没有任何序列 ID(例如，如果存在现有的多列主键)，您仍然可以使用 IN 来过滤要删除的行:

DELETE FROM table_name
WHERE (key1, key2) IN (
    SELECT key1, key2 FROM table_name ORDER BY date DESC LIMIT 2
);

对于您的具体情况，您可以使用:

DELETE FROM users 
WHERE (user_id, group_id) IN (
    SELECT user_id, group_id FROM users
    WHERE user_id = %s AND group_id = %s
    ORDER BY message_date DESC
);