Trying to construct PostgreSQL Query to extract from JSON a text value in an object, in an array, in an object, in an array, in an object

问题

I am constructing an interface between a PostgreSQL system and a SQL Server system and am attempting to "flatten" the structure of the JSON data to facilitate this. I'm very experienced in SQL Server but I'm new to both PostgreSQL and JSON.

The JSON contains essentially two types of structure: those of type "text" or "textarea" where the value I want is in an object named value (the first two cases below) and those of type "select" where the value object points to an id object in a lower-level options array (the third case below).

{
    "baseGroupId": {
        "fields": [
            {
                "id": "1f53",
                "name": "Location",
                "type": "text",
                "options": [],
                "value": "Over the rainbow"
            },
            {
                "id": "b547",
                "name": "Description",
                "type": "textarea",
                "options": [],
                "value": "A place of wonderful discovery"
            },
            {
                "id": "c12f",
                "name": "Assessment",
                "type": "select",
                "options": [
                    {
                        "id": "e5fd",
                        "name": "0"
                    },
                    {
                        "id": "e970",
                        "name": "1"
                    },
                    {
                        "id": "0ff4",
                        "name": "2"
                    },
                    {
                        "id": "2db3",
                        "name": "3"
                    },
                    {
                        "id": "241f",
                        "name": "4"
                    },
                    {
                        "id": "3f52",
                        "name": "5"
                    }
                ],
                "value": "241f"
            }
        ]
    }
}

Those with a sharp eye will see that the value of the last value object "241f" can also be seen within the options array against one of the id objects. When nested like this I need to extract the value of the corresponding name, in this case "4".

The JSON-formatted information is in table customfield field textvalue. It's datatype is text but I'm coercing it to json. I was originally getting array set errors when trying to apply the criteria in a WHERE clause and then I read about using a LATERAL subquery instead. It now runs but returns all the options, not just the one matching the value.

I'm afraid I couldn't get an SQL Fiddle working to reproduce my results, but I would really appreciate an examination of my query to see if the problem can be spotted.

with cte_custombundledfields as
     (
            select
                   textvalue
                 , cfname
                 , json_array_elements(textvalue::json -> 'baseGroupId'->'fields') ->> 'name'  as name
                 , json_array_elements(textvalue::json -> 'baseGroupId'->'fields') ->> 'value' as value
                 , json_array_elements(textvalue::json -> 'baseGroupId'->'fields') ->> 'type'  as type
            from
                   customfield
     )
   , cte_custombundledfieldsoptions as
     (
            select *
                 , json_array_elements(json_array_elements(textvalue::json -> 'baseGroupId'->'fields') -> 'options') ->> 'name' as value2
            from
                   cte_custombundledfields                                                   x
                 , LATERAL json_array_elements(x.textvalue::json -> 'baseGroupId'->'fields') y
                 , LATERAL json_array_elements(y -> 'options')                               z
            where
                   type    = 'select'
                   and z ->> 'id' = x.value
     )
select *
from
       cte_custombundledfieldsoptions

回答1:

I posted a much-simplified rewrite of this question which was answered by Bergi.

How do I query a string from JSON based on another string within the JSON in PostgreSQL?

来源：https://stackoverflow.com/questions/59071226/trying-to-construct-postgresql-query-to-extract-from-json-a-text-value-in-an-obj