使用 IN 语句返回的行的顺序

Question

我知道INPostgres 中的语句不能保证返回行的顺序。例如，如果我这样做：

SELECT users.id FROM users WHERE users.id IN (13589, 16674, 13588)

我可能会得到这样的结果：

16674
13588
13589

但是，我希望返回的行尊重IN列表中的顺序，所以我在网上找到的解决方案很少，例如：

SELECT users.id FROM users WHERE users.id IN (13589, 16674, 13588)
ORDER BY POSITION(id::text in '(13589, 16674, 13588)')

或者

SELECT users.id FROM users WHERE users.id IN (13589, 16674, 13588)
ORDER BY id = 13589 desc,
         id = 16674 desc,
         id = 13588 desc;

我想知道是否有更好的方法来做到这一点，或者更好但更有效？

Answer 1

WITH ORDINALITY 在 Postgres 9.4+

随 Postgres 9.4 引入。手册：

When a function in the FROM clause is suffixed by WITH ORDINALITY, a bigint column is appended to the output which starts from 1 and increments by 1 for each row of the function's output. This is most useful in the case of set returning functions such as unnest().

SELECT u.*
FROM   unnest('{13589, 16674, 13588}'::int[]) WITH ORDINALITY AS x(id, order_nr)
JOIN   users u USING (id)
ORDER  BY x.order_nr;

array or set?

x IN (set) statements are rewritten internally in Postgres to x = ANY (array), which is equivalent:

SELECT users.id FROM users WHERE users.id = ANY ('{13589, 16674, 13588}')

You can see for yourself with EXPLAIN.

Postgres 9.3 or earlier

For now, to preserve the order of elements, you could:

SELECT u.*
FROM  (
   SELECT arr, generate_subscripts(arr, 1) AS order_nr
   FROM  (SELECT '{13589, 16674, 13588}'::int[]) t(arr)
   ) x
JOIN   users u ON u.id = x.arr[x.order_nr]
ORDER  BY x.order_nr;

db<>fiddle here

Further reading:

• How to preserve the original order of elements in an unnested array?