在T-SQL函数中使用while循环

Question

Non-database programmer here. It happens so, that I need to create a function in T-SQL which returns workdays count between given dates. I believe that the easiest how it's done is with while loop. Problem is, that as soon as I write something like

while @date < @endDate
begin

end

the statement won't execute, claiming "incorrect syntax near the keyword 'return'" (not very helpful). Where's the problem?

PS Full code:

ALTER FUNCTION [dbo].[GetNormalWorkdaysCount] (
@startDate DATETIME,
@endDate DATETIME
)   
RETURNS INT

AS
BEGIN
    declare @Count INT,
            @CurrDate DATETIME
    set @CurrDate = @startDate

    while (@CurrDate < @endDate)
    begin

    end

    return @Count
END
GO

Answer 1

Unlike some languages, the BEGIN / END pair in SQL Server cannot be empty - they must contain at least one statement.

---

As to your actual problem - you've said you're not a DB programmer. Most beginners to SQL tend to go down the same route - trying to write procedural code to solve the problem.

Whereas, SQL is a set-based language - it's usually better to find a set-based solution, rather than using loops.

In this instance, a calendar table would be a real help. Such a table contains one row for each date, and additional columns indicating useful information for your business (eg what you consider to be a working day). It then makes your query for working days look like:

SELECT COUNT(*) from Calendar
where BaseDate >= @StartDate and BaseDate < @EndDate and IsWorkingDay = 1

Populating the Calendar table becomes a one off exercise, and you can populate it with eg 30 years worth of dates easily.

Answer 2

Using any loop within SQL server is never a good idea :)

There are few better solutions, referring to one presented on StackOverflow already .