计算日期段内有几个星期几(SQL, Delphi) ,日期段内有几个星期天

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
,case
when DATEPART(weekday,@EndDate) = @WeekDay then @EndDate + 1
else @EndDate
end
) / 7

IF DATEPART(weekday,@StartDate)=@WeekDay
SELECT @WeekNum = @WeekNum + 1
ELSE IF (@EndDate > @StartDate) AND (DATEPART(weekday,@EndDate) = @WeekDay)
SELECT @WeekNum = @WeekNum + 1

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);

//相差的天数是是多少个星期
Result := Trunc(WeekSpan(lvDate1, lvDate2));

//如果最后一天是那天则加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;
var
lvDate1, lvDate2, lvTempDate: TDateTime;
begin
lvDate1 := Trunc(pvDate1);
lvDate2 := Trunc(pvDate2);
lvTempDate := lvDate1;
Result := 0;
while lvTempDate <= lvDate2 do
begin
if DayOfWeek(lvTempDate) in pvWeekDays then Inc(Result);
lvTempDate := IncDay(lvTempDate, 1);
end;
end;