The ‘Call Log’ SQL Problem

Once again it is time for a Phil Factor Speed Phreak Challenge and the prize is now a $100 Amazon voucher, and the privilege of displaying this rather nice trophy jpg on your blog / website / bedroom wall.

This time your task is simply to produce a summary report of the cost of international phone calls made within an organization on a week by week basis for both Users and Offices. You are allowed to use any method you see fit, you may also add any indexes, table-functions or views that you wish (though not an index view). Creation of these will not count to the overall execution time. If you are unsure if what you want to do might disqualify you, then please post a comment.

The table CallLog contains the log of every phone call, including which user called which number, when the call started and ended, and the office the user was in at the time. You will notice that it is not well normalized, since it is actually a view taken from several tables. Users are never in a fixed office, and can move from office to office at any point. Calls with a CallEnd equal to CallStart were not answered and can be safely ignored.

To calculate the cost of the call you need to use a lookup within the PhoneTariff table. The calls are prefixed by an area code corresponding to a country.

You must note that many of the call areas have the same starting character sequence , so calls made to numbers starting '35191' must be priced using the tariff of '35191' not '351'.

There is a rather elaborate charging system according to the length of the call. This means that you need to calculate the cost of the call as the minute by minute cost changes with the length of the call. These must be summed.

Looking at the PhoneTariffCharges table

PhoneTariffId UpToXMinutes PricePerMinute
------------- ------------ ---------------------
2865          8            0.4792
2865          31           0.18
2865          59           0.5702
2865          100          1.298

The first 8 minutes of the call will be 0.4792 per minute. 9 to 31 minutes will be 0.18 per minute 32 to 59 minutes will be 0.5702 per minute etc.... All ranges have a UpToXMinutes of 9999 so you dont need to worry about an upper limit. The calllength is rounded upto the nearest whole minute.

Here is the DDL to create the tables

CREATE TABLE [dbo].[CallLog](
    [CallLogId] [int] NOT NULL,
    [CallStart] [datetime] NOT NULL,
    [CallEnd] [datetime] NULL,
    [OfficeName] [varchar](20) NOT NULL,
    [UserName] [varchar](20) NOT NULL,
    [NumberDialled] [varchar](255) NULL
) ON [PRIMARY]

GO



CREATE TABLE [dbo].[PhoneTariff](
    [PhoneTariffId] [int] IDENTITY(1,1) NOT NULL,
    [CallArea] [char](6) NULL,
    [DateStart] [datetime] NULL,
    [DateEnd] [datetime] NULL,
    [HoursStart] [int] NULL,
    [HoursEnd] [int] NULL,
    [ConnectionCharge] [money] NULL
) ON [PRIMARY]

GO


CREATE TABLE [dbo].[PhoneTariffCharges](
    [PhoneTariffId] [int] NULL,
    [UpToXMinutes] [int] NULL,
    [PricePerMinute] [money] NULL
) ON [PRIMARY]

GO

and heres the link to the data. Use

bcp <yourdatabase>..CallLog in CallLog.out -c -E -T
bcp <yourdatabase>..PhoneTariff in PhoneTariff.out -c -E -T
bcp <yourdatabase>..PhoneTariffCharges in PhoneTariffCharges.out -c -E -T

to load the data in.

Heres the solution provided by our mediocre developer Robert Bar, please note a fix for an issue with the week number being taken from @CallEnd.

Drop Table #OfficeTotalByWeek
go
Drop Table #UserTotalByWeek
go

Create Table #OfficeTotalByWeek
(
WeekNo   integer,
Year     integer,
Office   varchar(255),
Total    money
)
go
Create Table #UserTotalByWeek
(
WeekNo   integer,
Year     integer,
UserName     varchar(255),
Total    money
)
go

/*  Routine  : Call Cost Calculate */
/*  Developer : R Bar (RB)            */

 declare @CallStart datetime,
         @CallEnd   datetime,
         @OfficeName varchar(255),
         @UserName   varchar(255),
         @NumberDialled varchar(255),
         @PhoneTariffId integer,
         @ConnectionCharge money,
         @RangeStart       datetime,
         @RangeEnd         datetime

 declare CalcCursor Cursor
 for Select CallStart,CallEnd,OfficeName,UserName,NumberDialled
        from CallLog
    --  where OfficeName = 'Marketing'
        --and UserName  = 'Yolanda Haley'

 open CalcCursor
 while(0=0) begin
    /* RB : For Each Call in CallLog */ 
    fetch next from CalcCursor into @CallStart,@CallEnd,@OfficeName,@UserName,@NumberDialled

    if(@@Fetch_Status <>0)   begin

       break
    end

     if(@CallStart = @CallEnd) begin  /* RB : If True then the call was not answered so no charge */
        continue
     end
    /* RB */
    /* Find the appropriate Tariff */
    /* The number dialled must match the CallArea */
    /* But as the length of the CallArea is variable */
    /* An index seek cannot be used */

    Declare @CallDatech varchar(15)
    Select @CallDatech = CONVERT(varchar(15),@CallStart,112)

    select @PhoneTariffId = NULL
    set rowcount 1
    Select @PhoneTariffID = PhoneTariffId,
           @ConnectionCharge = ConnectionCharge,
           @RangeStart       = DateStart,
           @RangeEnd         = DateEnd
      from phonetariff where @NumberDialled like rtrim(CallArea)+'%' 
       and @CallDateCh between DateStart and DateEnd
       and DatePart(hh,@CallStart) between HoursStart and HoursEnd

    order by len(CallArea) desc   /* RB : Order by is used so the longest CallArea is used */
    set rowcount 0


    if(@PhoneTariffId is null) begin 
        select 'early break out error ',@NumberDialled
    end
    Declare @CallLength integer
    Select @CallLength = ceiling((DATEDIFF(S,@CallStart,@CallEnd))/60.0)

    Declare @RollingBalance money

    Declare @UptoXminutes integer
    Declare @PricePerMinute money
    Declare @MinsThisIter integer

    /* RB : Start the CallCost at the Connection Charge */
    Select @RollingBalance = @ConnectionCharge

    --Select @ConnectionCharge as 'ConnectionCharge' 
    declare @PrevUptoXMinutes integer
    select @PrevUptoXMinutes =0
    Declare TimeCalc Cursor for
    Select UpToXMinutes,PricePerMinute
      from Phonetariffcharges 
     where PhoneTariffId = @PhoneTariffID
    order by UpToXMinutes
    Open timecalc
    /* RB : Now Loop through the minute by minute cost totalling up as we go */
    while(0=0) begin 
       fetch next from timecalc into  @UptoXminutes,@PricePerMinute

       if(@@FETCH_STATUS <>0) begin
          select 'early break out error',@NumberDialled,@PhoneTariffId
          break
       end

       Declare @MinsToIter integer
       /* RB : Calculate how many minutes from this portion we need */
       Select @MinsThisIter = case when @uptoXminutes > @CallLength then @CallLength -@PrevUptoXMinutes
                                                                     else @uptoXminutes -@PrevUptoXMinutes
                                                                     end

       Select @RollingBalance = @RollingBalance +(@MinsThisIter*@PricePerMinute)
       Select @PrevUptoXMinutes = @uptoXminutes 
       if(@uptoXminutes>=@CallLength)begin /* RB : Have we accounted for each minute */
          break
       end

    end
    close TimeCalc
    Deallocate TimeCalc

    if(@PrevUptoXMinutes = 0) begin 
        select 'Charges Calc Error',@NumberDialled,@PhoneTariffId,@CallLength
    end
    Declare @Year integer
    Declare @WeekNo integer
    Select @Year=DATEPART(yy,@CallStart),
           @WeekNo=DATEPART(WEEK,@CallStart)


    /*  RB : Update the Users week-by-week total */
    Update #UserTotalByWeek
       set Total = Total + @RollingBalance
     where UserName =@UserName 
       and WeekNo = @WeekNo
       and Year = @Year
    if(@@ROWCOUNT=0) begin 
       /* RB : Or Create */
       insert into #UserTotalByWeek(UserName,WeekNo,Year,Total)
                          values(@UserName,@WeekNo,@Year,@RollingBalance)
    end
    /* RB : Update the Office week-by-week total */
    Update #OfficeTotalByWeek
       set Total = Total + @RollingBalance
     where Office = @OfficeName
       and WeekNo = @WeekNo
       and Year = @Year
    if(@@ROWCOUNT=0) begin 
       /* RB : Or Create */
       insert into #OfficeTotalByWeek(Office,WeekNo,Year,Total)
                          values(@OfficeName,@WeekNo,@Year,@RollingBalance)
    end    
 end
 close CalcCursor
 Deallocate CalcCursor

 go
 /* RB : Select the totals back */
 Select * from #OfficeTotalByWeek
 Select * from #UserTotalByWeek
 go
 Drop Table #OfficeTotalByWeek
go
Drop Table #UserTotalByWeek
go

Here are some guidelines for your entries:

1) Include a header in your suggestion. Make sure your name and the current date is present.

2) Include an edition number. First edition is 1. If you later improve your current suggestion post it again as version 2. Example: “Peso 1” and if improved, “Peso 1b”, “Peso 1c” etc.

3) If you are trying a new algorithm, change the edition to “Peso 2”. If you improve this algorithm, change the version to “Peso 2b”, “Peso 2c” etc. This will save Phil hours of work in the test harness!

4) The solution must clear up all its mess (temporary tables, indexes, etc.) so it can be re-run without errors.

As ever Phil Factor will be final judge.

The closing date will be midnight Thursday 17th December London