Question

我遇到的问题是postgres有序的结果不是一致的。我按多个字段排序：ORDER BY categories.position ASC，photos.display_priority

我注意到这一点，因为当您浏览网站时，结果会被分页。我找到了一个从第1页到第2页的案例，在第2页的顶部，我看到了第1页底部附近的照片。

这是我的第1页查询：

SELECT "photos".*
FROM "photos"
    INNER JOIN "categories" ON "categories"."id" = "photos"."category_id"
WHERE "photos"."category_id" IN (221, 633, 377, 216, 634)
    AND (photos.caption IS NOT NULL
        AND photos.category_id IS NOT NULL
        AND photos.rights IS NOT NULL
        AND photos.deleted IS NULL)
ORDER BY categories.position ASC, photos.display_priority DESC
LIMIT 25 OFFSET 0;

我的第2页查询：

SELECT "photos".*
FROM "photos"
    INNER JOIN "categories" ON "categories"."id" = "photos"."category_id"
WHERE "photos"."category_id" IN (221, 633, 377, 216, 634)
    AND (photos.caption IS NOT NULL
        AND photos.category_id IS NOT NULL
        AND photos.rights IS NOT NULL
        AND photos.deleted IS NULL)
ORDER BY categories.position ASC, photos.display_priority DESC
LIMIT 25 OFFSET 25;

当我尝试同时获取两个页面（偏移0，限制50）并检查两组之间的阈值时，没有重复，没有意外。

SELECT "photos".*
FROM "photos"
    INNER JOIN "categories" ON "categories"."id" = "photos"."category_id"
WHERE "photos"."category_id" IN (221, 633, 377, 216, 634)
    AND (photos.caption IS NOT NULL
        AND photos.category_id IS NOT NULL
        AND photos.rights IS NOT NULL
        AND photos.deleted IS NULL)
ORDER BY categories.position ASC, photos.display_priority DESC
LIMIT 50 OFFSET 0;

我的查询有问题吗？是否有我不理解的限制和顺序的操作顺序？

Answer 1

听起来categories.position和photos.display_priority对于所有结果行都不是唯一的。当用于排序它们的值全部相等时，数据库服务器不指定行的顺序;即使表格数据在查询之间没有变化，也可以按任意顺序返回它们。

要获得一致的排序，您必须添加第三个排序键，保证所有行都是唯一的，例如该特定行的标识值。

Postgres订购不一致

1 个答案: