如何根据数组元素的顺序对查询结果进行排序？

Question

我在 Postgres 9.4 中有这个查询：

select id from question where id = any(
    array_cat(
        ARRAY[0,579489,579482,579453,561983,561990,562083]::integer[], 
        (select array(
            select id from question where id not in 
                (0,579489,579482,579453,561983,561990,562083)
            and status in (1, -1) 
            and created_at > 1426131436 order by id desc offset 0 limit 10 )
        )::integer[]
    )
)

返回：

   id
--------
 561983
 561990
 562083
 579453
 579482
 579489
 580541
 580542
 580543
 580544
 580545
 580546
 580547
 580548
 580549
 580550
(16 rows)

但它的顺序不正确。我需要根据子数组的结果排序的结果：

array_cat(
        ARRAY[0,579489,579482,579453,561983,561990,562083]::integer[], 
        (select array(
            select id from question where id not in 
                (0,579489,579482,579453,561983,561990,562083)
            and status in (1, -1) 
            and created_at > 1426131436 order by id desc offset 0 limit 10 )
        )::integer[]
    )

我该怎么做？

Answer 1

基础知识：

• PostgreSQL unnest() with element number

由于您使用的是 Postgres 9.4，因此您可以使用新的 WITH ORDINALITY：

WITH t AS (
   SELECT *
   FROM   unnest('{0,579489,579482,579453,561983,561990,562083}'::int[])
                  WITH ORDINALITY AS t(id, rn)
   )
(
SELECT id
FROM   question
JOIN   t USING (id)
ORDER  BY t.rn
)
UNION ALL
(
SELECT id
FROM   question
LEFT   JOIN t USING (id)
WHERE  t.id IS NULL
AND    status IN (1, -1) 
AND    created_at > 1426131436
ORDER  BY id DESC
LIMIT  10
);

解释

1. 由于您两次使用相同的数组，我在查询前添加了一个 CTE，您可以在其中提供数组一次。 unnest()它立即WITH ORDINALITY根据数组元素的顺序获取行号（rn）。

2. 不要将子查询填充到数组中并将其转换回来，而是直接使用它。便宜得多。排序顺序直接来源于id。

3. 使用LEFT JOIN / IS NULL，而不是使用NOT IN（这对于NULL 值可能会很棘手）从给定数组中排除ID：

   • Select rows which are not present in other table

4. 只需将两个部分附加UNION ALL。在 UNION ALL 查询的每条腿上，括号必须有单独的 ORDER BY：

   • Sum results of a few queries and then find top 5 in SQL

5. 最后的SELECT 中的JOIN 到question 现在是多余的，我把它去掉了。

Answer 2

ORDER BY idx(your_array, your_element)

或

ORDER BY your_array # your_element

intarray

select id from question where id = any(
    array_cat(
        ARRAY[0,579489,579482,579453,561983,561990,562083]::integer[], 
        (select array(
            select id from question where id not in 
                (0,579489,579482,579453,561983,561990,562083) and status in (1, -1) 
                and created_at > 1426131436 order by id desc offset 0 limit 10 )
        )::integer[]
    ) 
) ORDER BY array_cat(
    ARRAY[0,579489,579482,579453,561983,561990,562083]::integer[], 
    (select array(
        select id from question where id not in 
            (0,579489,579482,579453,561983,561990,562083) and status in (1, -1) 
            and created_at > 1426131436 order by id desc offset 0 limit 10 )
    )::integer[]
) # id