計算日期段内有幾個星期幾(SQL, Delphi) ,日期段内有幾個星期天

declare @StartDate datetime

declare @EndDate datetime

declare @WeekDay INT, @WeekNum INT

set @StartDate = '2009-10-4' 

set @EndDate = '2009-10-25'

set @StartDate = '2009-10-1' 

set @EndDate = '2009-10-2'

set @StartDate = '2009-10-3' 

set @EndDate = '2009-10-4'

SET @WeekDay = 1   --星期天

SELECT @WeekNum=datediff(day

                 ,case

                     when DATEPART(weekday,@StartDate) = @WeekDay then @StartDate - 1

                     else @StartDate

                  end

                      when DATEPART(weekday,@EndDate) = @WeekDay then @EndDate + 1

                      else @EndDate

             ) / 7

IF DATEPART(weekday,@StartDate)=@WeekDay

  SELECT @WeekNum = @WeekNum + 1

ELSE IF (@EndDate > @StartDate) AND (DATEPART(weekday,@EndDate) = @WeekDay)

SELECT @WeekNum

-----Delphi

function WeekDayCount(pvDate1, pvDate2: TDateTime; pvWeekDay: Integer): Integer;

var

  lvDate1, lvDate2: TDateTime;

  lvWeekNum: Real;

  lvDay: Integer;

begin

  lvDate1 := Trunc(pvDate1);

  lvDate2 := Trunc(pvDate2);

  if DayOfWeek(pvDate1) = pvWeekDay then lvDate1 := IncDay(lvDate1, -1);

  if DayOfWeek(lvDate2) = pvWeekDay then lvDate2 := IncDay(lvDate2, +1);

  //相差的天數是是多少個星期

  Result := Trunc(WeekSpan(lvDate1, lvDate2));

  //如果最後一天是那天則加1，注意是pvDate2不是lvDate2

  if DayOfWeek(pvDate1) = pvWeekDay then Inc(Result)

  else if pvDate2 > pvDate1 then

    if DayOfWeek(pvDate2) = pvWeekDay then Inc(Result);

end;

type

  TWeekDay = 1..7;

  TWeekDays = set of TWeekDay;

function WeekDayCountEx(pvDate1, pvDate2: TDateTime; pvWeekDays: TWeekDays):

  Integer;

  lvDate1, lvDate2, lvTempDate: TDateTime;

  lvTempDate := lvDate1;

  Result := 0;

  while lvTempDate <= lvDate2 do

  begin

    if DayOfWeek(lvTempDate) in pvWeekDays then Inc(Result);

    lvTempDate := IncDay(lvTempDate, 1);

  end;