如何在postgres查询中解析json数组

Question

I need to parse json array from below table column. The result should be answer of Q2 question in below example.

id      data
1   [{"questionId":"Q1","answer":"A1"},{"questionId":"Q2","answer":"A2"}]
2   [{"questionId":"Q1","answer":"A1"},{"questionId":"Q2","answer":"A2"}]

So the result should be like this

1 A2
2 A2

I tried with data::json->'answer' as answer but doesn't seem to work on array

Answer 1

You may use json_array_elements and filter rows using a WHERE clause

select id, j->>'answer' as answer FROM t 
cross join lateral json_array_elements(data::json) as j
WHERE j->>'questionId' = 'Q2'

Demo

Answer 2

Try the ># operator .

create temporary table t (id serial primary key, data json);
insert into t (
  data
)
values (
  '[{"questionId":"Q1","answer":"A1"},{"questionId":"Q2","answer":"A2"}]'
);
insert into t (
  data
)
values (
  '[{"questionId":"Q1","answer":"A1"},{"questionId":"Q2","answer":"A2"}]'
);

-- The Q1 ist the 2nd element in the array and has index 1.
select id, data::json#>'{1,answer}' from t;

Output:

+------+------------+
| id   | ?column?   |
|------+------------|
| 1    | "A2"       |
| 2    | "A2"       |
+------+------------+