SQL Server 自定义函数返回格式化DateTime

Create FUNCTION [dbo].[FormatDateTime]
(@date as datetime,---传入时间
@dformat as varchar(10)---传入要生成的格式代码
)
RETURNS varchar(100) AS  
BEGIN 
	declare @datestring as varchar(100)
	if @dformat='f1'
	begin
		set @datestring=(SELECT FORMAT(@date, 'yyyy-MM-dd HH:mm:ss.fff'))
	end
	if @dformat='f2'
	begin
		set @datestring=(SELECT FORMAT(@date, 'yyyy-MM-dd HH:mm:ss'));
	end
	if @dformat='f3'
	begin
		set @datestring=(SELECT FORMAT(@date, 'yyyyMMddHHmmss'));
	end
	if @dformat='f4'
	begin
		set @datestring=(SELECT FORMAT(@date, 'yyyy/MM/dd HH:mm:ss'));
	end
	if @dformat='f5'
	begin
		set @datestring=(SELECT FORMAT(@date, 'yyyy/MM/dd HH:mm:ss.fff'));
	end
	if @dformat='f6'
	begin
		set @datestring=(SELECT FORMAT(@date, 'yyyy/MM/dd HH:mm:ss:fff'));
	end
	if @dformat='f7'
	begin
		set @datestring=(SELECT FORMAT(@date, 'yyyy-MM-dd HH:mm:ss:fff'));
	end
	return @datestring
END