postgres array_agg with distinct on json_build_object

Question

select 
  t1.id,
  array_agg(
    json_build_object('id', t2.id, 'status', t2.status)
  ) as statuses
from table1 t1
inner join table2 t2 on t1.id=t2.user_id   
inner join table3 t3 on t1.id=t3.user_id
group by t1.id

table1 
id  ,  user
1   ,  'A'
2   ,  'B'

table2
user_id  ,  status
1   ,  'P'
1   ,  'AP'

table3
user_id  ,  something
1   ,  'A12'
1   ,  'B1212'

the table3 also one-many relationship as a result the duplication of statuses coming in the array_agg, i tried with array_agg(distinct json_build_object()) and array_agg(distinct on json_build_object()), how can we prevent duplications in this case ??

Answer 1

Just filter out the relevant status as join condition (1):

select 
  t1.id,
  array_agg(
    json_build_object('id', t2.id, 'status', t2.status)
  ) as statuses
from table1 t1
inner join table2 t2 on t1.id=t2.user_id   
inner join table3 t3 on t1.id=t3.user_id 
   and t3.status = 'A12'                   -- 1.
group by t1.id

Furthermore, if you want to get valid JSON arrays, you should use json_agg() instead of array_agg():

select 
  t1.id,
  json_agg(
    json_build_object('id', t2.id, 'status', t2.status)
  ) as statuses
from table1 t1
inner join table2 t2 on t1.id=t2.user_id   
inner join table3 t3 on t1.id=t3.user_id 
   and t3.status = 'A12'               
group by t1.id