Select the first and last log records for a request (Group by CorrelationId)

HttpApiLogRecords_queries.sql

-- http://stackoverflow.com/questions/3800551/sql-select-first-row-in-each-group-by-group
-- http://dbaspot.com/sqlserver-programming/363437-union-two-ctes-together.html
-- http://stackoverflow.com/questions/354224/combining-union-all-and-order-by-in-firebird
WITH FirstLogs AS (
  SELECT 
    l.[CorrelationId], 
    l.[Timestamp],
    ROW_NUMBER() OVER(PARTITION BY l.[CorrelationId] ORDER BY l.[Timestamp] ASC) AS rk
  FROM [DependencyScopeTracingDisposeBug.Models.Entities.WebApiTracerContext].[dbo].[HttpApiLogRecords] l
),
LastLogs AS (
  SELECT 
    l.[CorrelationId], 
    l.[Timestamp],
    ROW_NUMBER() OVER(PARTITION BY l.[CorrelationId] ORDER BY l.[Timestamp] DESC) AS rk
  FROM [DependencyScopeTracingDisposeBug.Models.Entities.WebApiTracerContext].[dbo].[HttpApiLogRecords] l
)
SELECT * FROM  (
  SELECT fl.[CorrelationId], fl.[Timestamp] FROM FirstLogs fl WHERE fl.rk = 1
  UNION ALL
  SELECT ll.[CorrelationId], ll.[Timestamp] FROM LastLogs ll WHERE ll.rk = 1
) AS Logs
ORDER BY [CorrelationId];