AWS Athena：不支持的相关子查询类型，但它适用于 Mysql 和其他风格

Question

对于订单表中的每个订单，我都在尝试根据 time_sent 返回最新的订单更新值，并分组为一行。

CREATE TABLE order_updates (time_sent INTEGER, order_id INTEGER, a VARCHAR(2), b VARCHAR(2), c VARCHAR(2), d VARCHAR(2));

INSERT INTO order_updates (time_sent, order_id, a, b, c, d) VALUES
('1', '1', 'a1', null, null, null),
('2', '1', null, 'b1', null, null),
('3', '1', null, null, 'c0', null),
('4', '1', 'a3', null, 'c3', null),
('5', '1', 'a0', null, null, null),
('6', '2', 'a3', 'b0', null, 'd2'),
('7', '2', null, 'b3', null, null);

CREATE TABLE orders (order_id INTEGER, name VARCHAR(32));
insert into orders (order_id, name) values (1, "joe"), (2, "bill");

select *, (select order_updates.a from order_updates where order_updates.order_id = orders.order_id and order_updates.a is not null order by order_updates.time_sent desc limit 1) a,
(select order_updates.b from order_updates where order_updates.order_id = orders.order_id and order_updates.b is not null order by order_updates.time_sent desc limit 1) b,
(select order_updates.c from order_updates where order_updates.order_id = orders.order_id and order_updates.c is not null order by order_updates.time_sent desc limit 1) c,
(select order_updates.d from order_updates where order_updates.order_id = orders.order_id and order_updates.d is not null order by order_updates.time_sent desc limit 1) d
FROM orders;

上述选择查询在 MySql 中可以正常工作，但在 AWS Athena 中却不行。

下面的工作 MySQL 示例：

https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=66f17cf9f3c8f19f758c7cb1381d8207

有没有办法使用连接来完成上述操作？

Answer 1

可以使用窗口函数来实现这一点 - 如Athena/Presto 0.172 中提供的，这里是获取列 a 和 b 的示例，可扩展为 c 和 d：

with order_updates_a as
(
    select order_id,a
    ,ROW_NUMBER()OVER(partition by order_id order by time_sent desc) nr
    from order_updates
    where a <> '' and a is not null
)
,order_updates_b as
(
    select order_id,b
    ,ROW_NUMBER()OVER(partition by order_id order by time_sent desc) nr
    from order_updates
    where b <> '' and b is not null
)
,order_updates_c as
(
    select order_id,c
    ,ROW_NUMBER()OVER(partition by order_id order by time_sent desc) nr
    from order_updates
    where c <> '' and c is not null
)
,order_updates_d as
(
    select order_id,d
    ,ROW_NUMBER()OVER(partition by order_id order by time_sent desc) nr
    from order_updates
    where d <> '' and d is not null
)
select o.*
,a.a
,b.b
,c.c
,d.d
from order o
left join order_updates_a a
    on o.order_id = a.order_id and a.nr = 1
left join order_updates_b b
    on o.order_id = b.order_id and b.nr = 1
left join order_updates_c c
    on o.order_id = c.order_id and c.nr = 1
left join order_updates_d d
    on o.order_id = d.order_id and d.nr = 1