SQL Error while trying to extract nested json data - sql

Question

I am running an SQL query to extract nested JSON data.
SELECT watsonResponse.responseId,
watsonResponse.chatId,
d.*
FROM watson_response_table watsonResponse
CROSS JOIN LATERAL (
SELECT d2.*
FROM jsonb_array_elements(watsonResponse.watsonresponse_output) AS d(events)
CROSS JOIN LATERAL (
SELECT d2.events ->> 'data' AS watsonResponse_ouput_data
, d2.events ->> 'text' AS watsonResponse_output_text
, d2.events ->> 'uiActionCode' AS watsonResponse_output_uiActionCode
FROM jsonb_array_elements(d.events) AS d2(events)
) d2
WHERE d.events ->> 'uiActionCode' = 'TextWithButton'
) d;
It fails with message SQL Error [22023]: ERROR: cannot extract elements from an object
I am using PostgresSQL 11+. Here is what the JSON looks like,
[
{
"text": [
"Some text!"
],
"uiActionCode": "textOnly"
},
{
"data": {
"type": "options",
"options": [
{ "label": "test", "value": "testvalue" },
{ "label": "test2", "value": "testvalue2" },
{
"label": "test3",
"value": "testQuestion?"
}
]
},
"text": ["testQuestion2?"],
"uiActionCode": "TextWithButton"
}
]

Answer 1

If I am following this correctly, one level of unnesting is sufficient. You can then use the JSON accessors to get the results you want:
SELECT
r.responseId,
r.chatId,
d.events ->> 'uiActionCode' AS output_uiActionCode,
d.events -> 'text' ->> 0 AS output_text,
d.events -> 'data' AS output_data,
FROM watson_response_table watsonResponse r
CROSS JOIN LATERAL jsonb_array_elements(r.watsonresponse_output) AS d(events)
WHERE d.events ->> 'uiActionCode' = 'TextWithButton'
Note that there is an important difference between accessors -> and ->>. The former returns an object, while the latter returns a text value. You need to carefully pick the correct operator according to what needs to be done for each field.