User defined function with while loop in SQL Server

问题

I am asked to create a user defined function in SQL Server to returns the following pattern (for example, if the input = 5):

*****
 ****
  ***
   **
    *

Here is my code:

alter function udf_star (@input int)
returns varchar (200)
as 
begin 
    declare @star int 
    set @star = @input 

    declare @space int 
    set @space = 0

    while @star > 0
    begin 
        declare @string varchar (200)
        set @string = replicate (' ', @space) + replicate ('*', @star)

        set @star = @star - 1
        set @space = @space + 1  
    end 

    return @string 
end 

When I execute the function

select dbo.udf_star (5)

it only shows

'    *'

(4 spaces + 1 star); can anyone points out how should I correct the syntax?

Thanks in advance!

回答1:

It seems you may want a Table-Valued Function.

Also, loops should be avoided when possible

Example

CREATE FUNCTION [dbo].[tvf-Star] (@Input int)
Returns Table 
As
Return (  

Select Top (@Input) 
       Stars = replicate(' ',@Input-N)+replicate('*',N)
 From ( Select Top (@Input) N=Row_Number() Over (Order By (Select NULL)) From master..spt_values n1 ) A
 Order By N Desc
)

If you were to :

Select * from [dbo].[tvf-Star](5)

The Results

Stars
*****
 ****
  ***
   **
    *

来源：https://stackoverflow.com/questions/61125707/user-defined-function-with-while-loop-in-sql-server