How to query from JSON arrays from two different tables? - sql

Question

I have a table name doc_definition with a json column definition which has a format like:
[{
"id":"0",
"name:"Ques1"
},{
"id":"1",
"name:"Ques2"
},{
"id":"2",
"name:"Ques3"
}]
and another table doc which has another json column def_val with format as:
{
"0":{
"value":"Ans1"
},
"1":{
"value":"Ans2"
},
"2":{
"value":"Ans3"
}
}
I want to create a Postgres SQL query that gives the value of a corresponding question by matching the id field inside both json.
SO far I've come up with this:
SELECT json_array_elements(def.definition) ->> 'name' AS json_test
FROM document_definitions AS def
INNER JOIN documents AS doc
ON doc.document_definition_id = def.id
WHERE doc.id = 892 AND json_array_elements(def.definition) ->> 'name' = 'Ques2'
But this throws exception:
ERROR: argument of AND must not return a set
When i put the json_array_elements(def.definition) ->> 'name' = 'Ques2' in SELECT clause, it returns boolean value.
I dont know whats wrong then. Plz Help?

Answer 1

How about that query :
SELECT json_array_elements(def.definition) ->> 'name' AS json_test
FROM document_definitions AS def
INNER JOIN documents AS doc
ON doc.document_definition_id = def.id
WHERE doc.id = 892 AND (json_array_elements(def.definition) ::json->> 'name') = 'Ques2'

Answer 2

After many trial and errors, I've come up with this.
Plz let me know if I can improve this in any way.
SELECT definition_json.definition_value -> definition_json.def_value_id ->> 'value' AS definition_value
FROM (
SELECT json_array_elements(def.definition) ->> 'name' = 'Ques2' AS is_definition_present,
json_array_elements(def.definition) ->> 'id' AS def_value_id,
doc.definition_value, doc.id AS document_id, def.id AS definition_id
FROM document_definitions AS def
INNER JOIN documents AS doc
ON doc.document_definition_id = def.id
) AS definition_json
WHERE definition_json.is_definition_present = 't' AND definition_json.document_id = 892