参考https://www.cnblogs.com/xxaxx/p/4679480.html
1、PadLeft函数
向已知字符串左边补充字符，使整个字符串到达指定长度
CREATE FUNCTION PadLeft
(
@VarOrgan varchar(10),/原始字符/
@TotalLength int,/总长度/
@Placeholder varchar(1)/占位符/
)
RETURNS varchar(100)
AS
BEGIN
declare @VarNew varchar(100),
@PadLen int
SET @VarNew=@VarOrgan
SET @PadLen=@TotalLength-LEN(@VarOrgan)
while(@PadLen>0)
begin
select @VarNew=@Placeholder+@VarNew
set @PadLen=@PadLen-1
end
return @VarNew
END

2、PadRight
向已知字符串右边补充字符，使整个字符串到达指定长度

CREATE FUNCTION PadRight
(
@VarOrgan varchar(10),/原始字符/
@TotalLength int,/总长度/
@Placeholder varchar(1)/占位符/
)
RETURNS varchar(100)
AS
BEGIN
declare @VarNew varchar(100),
@PadLen int
SET @VarNew=@VarOrgan
SET @PadLen=@TotalLength-LEN(@VarOrgan)
while(@PadLen>0)
begin
select @VarNew=@VarNew+@Placeholder
set @PadLen=@PadLen-1
end
return @VarNew
END