Функция для подсчета временных интервалов

USE [oktell_cc_temp]
GO
/****** Object:  UserDefinedFunction [dbo].[SetLenForTimeIntervals]    Script Date: 28.06.2019 15:10:11 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:      <Author,,Name>
-- Create date: <Create Date,,>
-- Description: <Description,,>
-- =============================================
ALTER FUNCTION [dbo].[SetLenForTimeIntervals] (@idTask uniqueidentifier, @idOperator uniqueidentifier, @state int, @dateStart datetime, @timeStart datetime, @dateTimeStop datetime, @Interval nvarchar(20)) RETURNS
    @returnTable TABLE(IdTask uniqueidentifier, IdOperator uniqueidentifier, [State] int, DateStart datetime, TimeStart datetime, DateTimeStop datetime, Interval nvarchar(20), LenTime float)
AS
BEGIN
    DECLARE @START_TIME time
    DECLARE @END_TIME time
    DECLARE @TABLE_INTERVALS TABLE(Interval nvarchar(20), TimeStart time, TimeEnd time)

    SET @START_TIME = CAST(@timeStart as time)
    SET @END_TIME = CAST(@dateTimeStop as time)

    INSERT INTO @TABLE_INTERVALS
    SELECT Interval, TimeStart, TimeEnd
    FROM [oktell_cc_temp].[dbo].[Time_Intervals_At_Day]
    WHERE @Interval = Interval

    INSERT INTO @returnTable
    SELECT @idTask
        ,@idOperator
        ,@state
        ,@dateStart
        ,@timeStart
        ,@dateTimeStop
        ,@Interval
        ,IIF(@START_TIME >= TimeStart AND @END_TIME <= TimeEnd, datediff(second, @START_TIME, @END_TIME), -1) as LenTime
    FROM @TABLE_INTERVALS
    WHERE IIF(@START_TIME >= TimeStart AND @END_TIME <= TimeEnd, datediff(second, @START_TIME, @END_TIME), -1) != -1
    UNION
    SELECT @idTask
        ,@idOperator
        ,@state
        ,@dateStart
        ,@timeStart
        ,@dateTimeStop
        ,@Interval
        ,IIF(@START_TIME >= TimeStart AND @END_TIME >= TimeEnd AND @START_TIME <= TimeEnd, datediff(second, @START_TIME, TimeEnd), -1) as LenTime
    FROM @TABLE_INTERVALS
    WHERE IIF(@START_TIME >= TimeStart AND @END_TIME >= TimeEnd AND @START_TIME <= TimeEnd, datediff(second, @START_TIME, TimeEnd), -1) != -1
    UNION
    SELECT @idTask
        ,@idOperator
        ,@state
        ,@dateStart
        ,@timeStart
        ,@dateTimeStop
        ,@Interval
        ,IIF(@END_TIME >= TimeStart AND @START_TIME <= TimeStart AND @END_TIME <= TimeEnd, datediff(second, TimeStart, @END_TIME), -1) as LenTime
    FROM @TABLE_INTERVALS
    WHERE IIF(@END_TIME >= TimeStart AND @START_TIME <= TimeStart AND @END_TIME <= TimeEnd, datediff(second, TimeStart, @END_TIME), -1) != -1
    UNION
    SELECT @idTask
        ,@idOperator
        ,@state
        ,@dateStart
        ,@timeStart
        ,@dateTimeStop
        ,@Interval
        ,IIF(@START_TIME <= TimeStart AND @END_TIME >= TimeEnd, 3600, -1) as LenTime
    FROM @TABLE_INTERVALS
    WHERE IIF(@START_TIME <= TimeStart AND @END_TIME >= TimeEnd, 3600, -1) != -1

    RETURN;
END