Postgres LIMIT/OFFSET 奇怪的行为

我正在使用 PostgreSQL 9.6。我有一个这样的查询：

SELECT anon_1.id AS anon_1_id, anon_1.is_valid AS anon_1_is_valid, anon_1.first_name AS anon_1_first_name, anon_1.last_name AS anon_1_last_name,
anon_1.patronymic_name AS anon_1_patronymic_name,
anon_1.experience AS anon_1_experience, anon_1.user_id AS anon_1_user_id, anon_1.rating_points as rating_points

FROM (SELECT DISTINCT ON (doctors.id) doctors.id AS id, doctors.created_at AS created_at, doctors.updated_at AS updated_at, doctors.is_valid AS is_valid, doctors.pretty_url AS pretty_url, doctors.first_name AS first_name, doctors.last_name AS last_name, doctors.patronymic_name AS patronymic_name, doctors.phone AS phone, doctors.birthday AS birthday, doctors.avatar AS avatar, doctors.experience AS experience, doctors.science_degree AS science_degree, doctors.sex_id AS sex_id, doctors.yclients_staff_id AS yclients_staff_id, doctors.user_id AS user_id, doctor_has_specialties.rating_points AS rating_points, clinic_branch_has_doctors.price AS price, clinic_branch_has_doctors.doctor_type AS doctor_type, clinic_branch_has_doctors.is_house_call AS is_house_call, clinic_branch_has_doctors.house_call_price AS house_call_price 
FROM doctors
      JOIN doctor_has_specialties ON doctors.id = doctor_has_specialties.doctor_id 
      JOIN clinic_branch_has_doctors ON doctor_has_specialties.id = clinic_branch_has_doctors.doctor_has_specialty_id 
      JOIN clinic_branches ON clinic_branches.id = clinic_branch_has_doctors.clinic_branch_id 
      JOIN city_areas ON city_areas.id = clinic_branches.city_area_id 
      JOIN cities ON cities.id = city_areas.city_id 
WHERE doctors.is_valid = true 
      AND clinic_branch_has_doctors.is_valid = true 
      AND clinic_branches.is_valid = true 
      AND doctor_has_specialties.specialty_id = 1
      AND cities.id = 1) AS anon_1 ORDER BY anon_1.rating_points DESC 
 LIMIT 100 OFFSET 0

这里查询最重要的部分是最后一项，LIMIT 和 OFFSET。 当我运行此查询时，我获取最多 100 行的所有数据。一切都很好不是。这是 pgAdmin 的屏幕截图：

Here notice row with id 20. Now If I try to OFFSET 10, I get my data from 11th row as expected which is object with id 22. Everything is fine too. But If I try OFFSET 10 LIMIT 10, I get strange result. Mainly row with id 20 appears too, but it shouldn't. Here is the screenshot:

不知道这有什么问题。这是 Postgres 的错误吗？或者我做错了什么。

这里没有“错误”在起作用。您指定了以下顺序，该顺序在以下情况下使用：LIMIT and OFFSET正在应用：

ORDER BY anon_1.rating_points DESC

但是，如果两个或多个记录与相同的记录相关联rating_points值，Postgres 不保证顺序是什么。这就是为什么您会看到一个用户anon_id_1 of 20显然在四处走动。 Postgres 没有做错任何事；它已尊重您的订购请求rating_points，但你从未告诉它在领带的情况下该怎么做。

要解决此问题，您可以向ORDER BY:

ORDER BY
    anon_1.rating_points DESC,
    anon_id_1

这将打破订购方面的平局，并且假设anon_id_1是主键，进行此更改后结果将显得稳定。