Azure Data Factory: Get the max-value from a table with the help of CreatedAt-column within an variable expression

This time I am using the following manual:
https://techcommunity.microsoft.com/t5/azure-synapse-analytics-blog/extracting-sap-data-using-odata-part-7-delta-extraction-using/bc-p/4202197#M976
We are talking about this picture:

What are we trying to do:

Lookup: Get a table from source
Set variable: Check if the table is empty
If empty, write an empty value to variable
If filled, get the latest value from column DeltaToken with the help of column CreatedAt

My idea (I assumed that the DeltaToken does increase with time):

@if(equals(activity('ll_delta').output.count, 0), '', max(activity('ll_delta').output.value.DeltaToken))

Error:
The expression 'if(equals(activity('ll_delta').output.count, 0), '', max(activity('ll_delta').output.value.DeltaToken))' cannot be evaluated because property 'DeltaToken' cannot be selected. Array elements can only be selected using an integer index.

His idea:
Order the DeltaToken by its CreatedAt-Time and pull the latest --> Would anyone mind helping me to achieve this goal? I would appreciate your help

Edit_1
ll_delta:

ODataURL:

@concat(pipeline().parameters.URL, pipeline().parameters.ODataService, '/')

Entity:

@concat('DeltaLinksOf', pipeline().parameters.Entity)

Sample Output by ll_delta:

{
"count": 5,
"value": [
    {
        "DeltaToken": "D20240815145137_000036000",
        "CreatedAt": "2024-08-15T14:51:37Z",
        "IsInitialLoad": true
    },
    {
        "DeltaToken": "D20240815171231_000021000",
        "CreatedAt": "2024-08-15T17:12:31Z",
        "IsInitialLoad": false
    },
    {
        "DeltaToken": "D20240816091538_000017000",
        "CreatedAt": "2024-08-16T09:15:38Z",
        "IsInitialLoad": false
    },
    {
        "DeltaToken": "D20240816091955_000036000",
        "CreatedAt": "2024-08-16T09:19:55Z",
        "IsInitialLoad": false
    },
    {
        "DeltaToken": "D20240816092232_000119000",
        "CreatedAt": "2024-08-16T09:22:32Z",
        "IsInitialLoad": false
    }
],...

Our solution/workaround for now within activity Set variable/v_deltatoken (it does work):

@if(equals(activity('ll_delta').output.count, 0), '', last(activity('ll_delta').output.value).DeltaToken)

Issues:

We are not sure that the last value will always be the most recent one, hence I would like to get the max-value.
We have tried it by query the linked service via $orderby...desc incl. top1 and select but it seems as if the orderby-clause does not work as desired, hence we always pull the oldest one.
Next best solution could be something with ForEach but it seems to be very complicated, isn't it?

Solution

Order the DeltaToken by its CreatedAt-Time and pull the latest

To achieve your requirement, you need to first get the max CreatedAt and based on it you need to filter the output.

Here is the sample solution I tried with sample data you provided:

First as you did pull the data using lookup activity.
You need to get the max CreatedAt using the Foreach activity and set variables.

Pass the Lookup output to for each activity as below:

enter image description here

Under Foreach activity take two set variables of string type and as initial date, max date to get the max CreatedAt date as below:

enter image description here

Then filter the Lookup data using the max date you got after all iteration of for each activity

After this you will get the latest values.

OUTPUT:

enter image description here