如何在PostgreSQL中聚合具有可变键数的JSON数组？

我在PostgreSQL表中有一系列行，如下所示：

-[ RECORD 1 ]---------------------------------------------------------------------
student     | e04c0ae4709340cb8e03c52f444e723f
group       | 1
subgroup    | 1
variable    | VAR1
status      | { "track_A" : "Done", "track_B" : "Done", "track_C" : "To Do" }
-[ RECORD 2 ]---------------------------------------------------------------------
student     | e04c0ae4709340cb8e03c52f444e723f
group       | 1
subgroup    | 1
variable    | VAR2
status      | { "track_A" : "To Do", "track_B" : "Done", "track_C" : "To Do" }
-[ RECORD 3 ]---------------------------------------------------------------------
student     | 849d1e6a0c2b4530a2b550829df94556
group       | 0
subgroup    | 1
variable    | VAR3
status      | { "track_A" : "Done", "track_B" : "To Do", "track_C" : "To Do" }

我想按学生、组和子组对它们进行分组，并获得每个曲目的计数状态。比如：

-[ RECORD 1 ]---------------------------------------------------------------------
student     | e04c0ae4709340cb8e03c52f444e723f
group       | 1
subgroup    | 1
totals      | { "track_A" : {"done": 1, "to_do": 1}, {"track_B" : {"done": 0, "to_do": 2}, "track_C" : {"done": 0, "to_do": 2} }

问题是轨道的数量可能会有所不同。我知道它们的名字，但它们不是静态的，所以我无法进行简单的聚合。有什么建议我可以在PostgreSQL（9.5）中写这篇文章吗？我不想对所有轨迹进行迭代和聚合，因为操作需要一些时间。

您可以使用“取消测试”值并再次组合它

数据：

查询：

WITH cte AS
(
   SELECT student, "group", subgroup, k
     ,COUNT(CASE WHEN v='Done'  THEN 1 END) AS Done
     ,COUNT(CASE WHEN v='To Do' THEN 1 END) AS To_do
   FROM tab
   ,LATERAL json_each_text(status) s(k,v)
   GROUP BY student, "group", subgroup, k  
), cte2 AS
(
  SELECT student, "group", subgroup, k, json_object_agg(s.status, s.cnt) AS j
  FROM cte
  ,LATERAL (VALUES('Done', Done),('To Do', To_Do)) AS s(status, cnt)
  GROUP BY student, "group", subgroup, k   
)
SELECT student, "group", subgroup
      ,json_object_agg(k, j) AS totals
FROM cte2
GROUP BY student, "group", subgroup;

输出：

WITH cte AS
(
   SELECT student, "group", subgroup, k
     ,COUNT(CASE WHEN v='Done'  THEN 1 END) AS Done
     ,COUNT(CASE WHEN v='To Do' THEN 1 END) AS To_do
   FROM tab
   ,LATERAL json_each_text(status) s(k,v)
   GROUP BY student, "group", subgroup, k  
), cte2 AS
(
  SELECT student, "group", subgroup, k, json_object_agg(s.status, s.cnt) AS j
  FROM cte
  ,LATERAL (VALUES('Done', Done),('To Do', To_Do)) AS s(status, cnt)
  GROUP BY student, "group", subgroup, k   
)
SELECT student, "group", subgroup
      ,json_object_agg(k, j) AS totals
FROM cte2
GROUP BY student, "group", subgroup;