CTE with paging returning random value from subquery - sql

Question

I have a table with contact(contacts) information and another relationship table with key/value data for the contact table (customdata), the custom data rows are not unique, they can repeat, and they have a creation date as well.
I have a CTE querying the contacts, pretty simple, but I also want to return subquery column with from particular key, and the value from this query happens to contain a date, stored as varchar, and since this table does not contain unique rows I'm using TOP 1 and sorting by the row creation date.
The issue I'm having is that the value from the custom data table is returning random values and to top it off its not sorting correctly when casted to date.
WITH Customers_CTE AS(
SELECT row_number() over (ORDER BY (SELECT TOP 1 CONVERT(DATETIME, data_value, 101)
FROM CustomData
WHERE (data_cust_id = Customers.cust_id AND data_key = 'Sign Date' AND ISDATE(data_value) = 1) ORDER BY data_created DESC) DESC) AS rowNum,
COUNT(*) OVER (PARTITION BY NULL) AS [RowCount],
Customers.FirstName,
Customers.LastName,
(SELECT TOP 1 CONVERT(DATETIME, data_value, 101)
FROM CustomData
WHERE (data_cust_id = Customers.cust_id AND data_key = 'Sign Date' AND ISDATE(data_value) = 1) ORDER BY data_created DESC) AS DateSigned
FROM Customers)
SELECT * FROM Customers_CTE
WHERE rowNum >= 0 and rowNum < 10
Data sample
CUSTOMERS
cust_id, cust_firstname, cust_lastname
--------------------------------------
1 , john , doe
2 , jane , mary
CUSTOM DATA
data_created, data_cust_id, data_key , data_value
------------------------------------------------------
2018-04-06 , 1 , 'Sign Date' , '2018-03-17'
2018-04-06 , 1 , 'Agreed' , 'Yes'
2019-03-12 , 1 , 'Renew Date' , '2019-01-25'
2020-04-11 , 2 , 'Sign Date' , '2020-03-28'
2020-04-11 , 2 , 'Agreed' , 'Yes'
2020-06-07 , 1 , 'Sign Date' , '2020-05-13'
2020-10-21 , 2 , 'Sign Date' , '2020-09-15'
RESULT
FirstName , LastName , DateSigned
-------------------------------------
jane , mary , 2020-09-15
john , doe , 2020-05-13

Answer 1

I'm struggling to see what's going on with your CTE or what you are trying to do, it's just wriddled with syntax errors or issues.
If this helps, to get your desired output from your sample data, you just need the following - if I've understood your sample data you just want the maximum date value for each customer Id for a particular "key" value:
select c.cust_firstname, c.cust_lastname, d.DateSigned
from customers c
outer apply (
select Max(Try_Convert(date,data_value)) DateSigned
from customdata cd
where cd.data_cust_id=c.cust_id and cd.data_key='Sign date'
)d