Bigquery - 选择最后 # 个不同的值

Question

给定表格：

WITH table AS
(SELECT 'A' id, '11' ar, 1 ts   UNION ALL
SELECT 'A', '12', 2 UNION ALL
SELECT 'A', '11', 3 UNION ALL
SELECT 'B', '11', 4 UNION ALL
SELECT 'B', '13', 5 UNION ALL
SELECT 'B', '12', 6 UNION ALL
SELECT 'B', '12', 7)


id  ar  ts
A   11  1
A   12  2
A   11  3
B   11  4
B   13  5
B   12  6
B   12  7

我需要得到唯一的最后两行：

id  ar
A   11
A   12
B   12
B   13

我用DISTINCT 和LIMIT 尝试了ARRAY_AGG，

但是ORDER BY必须和表达式一样

Answer 1

以下是 BigQuery 标准 SQL

#standardSQL
SELECT * EXCEPT(ars) 
FROM (
  SELECT id, ARRAY_AGG(ar ORDER BY ts DESC LIMIT 2) AS ars
  FROM (
    SELECT id, ar, MAX(ts) AS ts 
    FROM `project.dataset.table`
    GROUP BY id, ar
  )
  GROUP BY id
) t, t.ars AS ar   

如果应用于您问题中的样本数据 - 输出是

Row id  ar   
1   A   11   
2   A   12   
3   B   12   
4   B   13