当多个节点共享相同的名称时，使用 Oracle SQL 获取 JSON_VALUE

Question

I have an issue where I have some JSON stored in my oracle database, and I need to extract values from it.

The problem is, there are some fields that are duplicated.

When I try this, it works as there is only one firstname key in the options array:

    SELECT 
    JSON_VALUE('{"increment_id":"2500000043","item_id":"845768","options":[{"firstname":"Kevin"},{"lastname":"Test"}]}', '$.options.firstname') AS value
   FROM DUAL;

Which returns 'Kevin'.

However, when there are two values for the firstname field:

SELECT JSON_VALUE('{"increment_id":"2500000043","item_id":"845768","options":[{"firstname":"Kevin"},{"firstname":"Okay"},{"lastname":"Test"}]}', '$.options.firstname') AS value
  FROM DUAL;

It only returns NULL.

Is there any way to select the first occurence of 'firstname' in this context?

Answer 1

JSON_VALUE returns one SQL VALUE from the JSON data (or SQL NULL if the key does not exists).

If you have a collection of values (a JSON array) an you want one specific item of the array you use array subscripts (square brackets) like in JavaScript, for example [2] to select the third item. [0] selects the first item. To get the first array item in your example you have to change the path expression from '$.options.firstname' to '$.options[0].firstname'

Answer 2

You can follow this query:-

SELECT JSON_VALUE('{
  "increment_id": "2500000043",
  "item_id": "845768",
  "options": [
    {
      "firstname": "Kevin"
    },
    {
      "firstname": "Okay"
    },
    {
      "lastname": "Test"
    }
  ]
}', '$.options[0].firstname') AS value
  FROM DUAL;