تابع FIRST_VALUE در SQL

SELECT DISTINCT od.Id,
                od.CreationDate,
                od.CustomerId,
                od.UserId,
                od.InstrumentId,
                od.Side,
                od.Price,
                od.Quantity,
                od.Status,
                od.Tags,
                COUNT(ode.Id) OVER (PARTITION BY od.Id)                                      AS ErrorCount,
                FIRST_VALUE(ode.Description) OVER (PARTITION BY od.Id ORDER BY ode.Id DESC)  AS ErrorDescription,
                FIRST_VALUE(ode.CreationDate) OVER (PARTITION BY od.Id ORDER BY ode.Id DESC) AS ErrorCreationDate
FROM [trm].[OrderDraft] od
          LEFT JOIN [trm].[OrderDraftError] ode ON ode.OrderDraftId = od.Id
WHERE od.UserId = @UserId
  AND od.Status < 5;

SELECT Name, ListPrice,   
       FIRST_VALUE(Name) OVER (ORDER BY ListPrice ASC) AS LeastExpensive   
FROM Production.Product  
WHERE ProductSubcategoryId = 10; 

SELECT JobTitle, LastName, VacationHours,   
       FIRST_VALUE(LastName) OVER (PARTITION BY JobTitle   
                                   ORDER BY VacationHours ASC  
                                   ROWS UNBOUNDED PRECEDING  
                                  ) AS FewestVacationHours  
FROM HumanResources.Employee AS e  
INNER JOIN Person.Person AS p   
    ON e.BusinessEntityId = p.BusinessEntityId  
ORDER BY JobTitle;