postgres:如何在给定条件的情况下计算数组列中的不同元素

Question

我有一个如下表:

ID     array1           array2
7333 | {615593}        | {NULL}
7333 | {2013682}       | {NULL}
7333 | {26573,1508291} | {NULL}
7333 | {1457957}       | {NULL}
7333 | {NULL}          | {1063105}
7333 | {NULL}          | {107978,408431}

我期待查询每个edge_id的array1和array2的所有唯一项.例如

ID   array1_distinct    array2_distinct
7333 5                  3

我尝试过类似下面的内容

SELECT 
  id, 
  array1_count 
FROM (
  SELECT id,
  COUNT(DISTINCT((CASE WHEN array1 is not null THEN (select unnest(array1)b) END)) as array1_count
  FROM mytable
  GROUP BY id
) totals
limit 1

我总是会遇到错误,例如"用作表达式的子查询返回的多行"和"在使用unfst时尝试计算数组中的元素时在上下文中调用的集值函数".

Answer 1

select id, count(distinct a1) as a1, count(distinct a2) as a2
from (
    select id, unnest(array1) as a1, unnest(array2) as a2
    from t
) s
group by id