Convert datetime to string formate in ms sql

first create a function in sql

CREATE function NUMBERTOWORDS(@n bigint )
--Returns the number as words.
returns VARCHAR(255)
as
BEGIN
DECLARE @i int, @temp char(1), @s VARCHAR(20), @result VARCHAR(255)
SELECT @s=convert(varchar(20), @n)
SELECT @i=LEN(@s)
SELECT @result=''
WHILE (@i>0)
BEGIN
SELECT @temp=(SUBSTRING(@s,@i,1))
IF ((LEN(@s)-@i) % 3)=1
IF @temp='1'
SELECT @result=CASE (SUBSTRING(@s,@i+1,1))
WHEN '0' THEN 'ten'
WHEN '1' THEN 'eleven'
WHEN '2' THEN 'twelve'
WHEN '3' THEN 'thirteen'
WHEN '4' THEN 'fourteen'
WHEN '5' THEN 'fifteen'
WHEN '6' THEN 'sixteen'
WHEN '7' THEN 'seventeen'
WHEN '8' THEN 'eighteen'
WHEN '9' THEN 'nineteen'
END+' '+CASE
WHEN ((LEN(@s)-@i)=4) THEN 'thousand '
WHEN ((LEN(@s)-@i)=7) THEN 'million '
WHEN ((LEN(@s)-@i)=10) THEN 'billion '
WHEN ((LEN(@s)-@i)=13) THEN 'trillion '
WHEN ((LEN(@s)-@i)=16) THEN 'quadrillion '
WHEN ((LEN(@s)-@i)=19) THEN 'quintillion '
WHEN ((LEN(@s)-@i)=22) THEN 'sextillion '
WHEN ((LEN(@s)-@i)=25) THEN 'septillion '
WHEN ((LEN(@s)-@i)=28) THEN 'octillion '
WHEN ((LEN(@s)-@i)=31) THEN 'nonillion '
WHEN ((LEN(@s)-@i)=34) THEN 'decillion '
WHEN ((LEN(@s)-@i)=37) THEN 'undecillion '
WHEN ((LEN(@s)-@i)=40) THEN 'duodecillion '
WHEN ((LEN(@s)-@i)=43) THEN 'tredecillion '
WHEN ((LEN(@s)-@i)=46) THEN 'quattuordecillion '
WHEN ((LEN(@s)-@i)=49) THEN 'quindecillion '
WHEN ((LEN(@s)-@i)=52) THEN 'sexdecillion '
WHEN ((LEN(@s)-@i)=55) THEN 'septendecillion '
WHEN ((LEN(@s)-@i)=58) THEN 'octodecillion '
WHEN ((LEN(@s)-@i)=61) THEN 'novemdecillion '
ELSE ''
END+@result
ELSE
BEGIN
SELECT @result=CASE (SUBSTRING(@s,@i+1,1))
WHEN '0' THEN ''
WHEN '1' THEN 'one'
WHEN '2' THEN 'two'
WHEN '3' THEN 'three'
WHEN '4' THEN 'four'
WHEN '5' THEN 'five'
WHEN '6' THEN 'six'
WHEN '7' THEN 'seven'
WHEN '8' THEN 'eight'
WHEN '9' THEN 'nine'
END+' '+ CASE
WHEN ((LEN(@s)-@i)=4) THEN 'thousand '
WHEN ((LEN(@s)-@i)=7) THEN 'million '
WHEN ((LEN(@s)-@i)=10) THEN 'billion '
WHEN ((LEN(@s)-@i)=13) THEN 'trillion '
WHEN ((LEN(@s)-@i)=16) THEN 'quadrillion '
WHEN ((LEN(@s)-@i)=19) THEN 'quintillion '
WHEN ((LEN(@s)-@i)=22) THEN 'sextillion '
WHEN ((LEN(@s)-@i)=25) THEN 'septillion '
WHEN ((LEN(@s)-@i)=28) THEN 'octillion '
WHEN ((LEN(@s)-@i)=31) THEN 'nonillion '
WHEN ((LEN(@s)-@i)=34) THEN 'decillion '
WHEN ((LEN(@s)-@i)=37) THEN 'undecillion '
WHEN ((LEN(@s)-@i)=40) THEN 'duodecillion '
WHEN ((LEN(@s)-@i)=43) THEN 'tredecillion '
WHEN ((LEN(@s)-@i)=46) THEN 'quattuordecillion '
WHEN ((LEN(@s)-@i)=49) THEN 'quindecillion '
WHEN ((LEN(@s)-@i)=52) THEN 'sexdecillion '
WHEN ((LEN(@s)-@i)=55) THEN 'septendecillion '
WHEN ((LEN(@s)-@i)=58) THEN 'octodecillion '
WHEN ((LEN(@s)-@i)=61) THEN 'novemdecillion '
ELSE ''
END+@result
SELECT @result=CASE @temp
WHEN '0' THEN ''
WHEN '1' THEN 'ten'
WHEN '2' THEN 'twenty'
WHEN '3' THEN 'thirty'
WHEN '4' THEN 'fourty'
WHEN '5' THEN 'fifty'
WHEN '6' THEN 'sixty'
WHEN '7' THEN 'seventy'
WHEN '8' THEN 'eighty'
WHEN '9' THEN 'ninety'
END+' '+@result
END
IF (((LEN(@s)-@i) % 3)=2) OR (((LEN(@s)-@i) % 3)=0) AND (@i=1)
BEGIN
SELECT @result=CASE @temp
WHEN '0' THEN ''
WHEN '1' THEN 'one'
WHEN '2' THEN 'two'
WHEN '3' THEN 'three'
WHEN '4' THEN 'four'
WHEN '5' THEN 'five'
WHEN '6' THEN 'six'
WHEN '7' THEN 'seven'
WHEN '8' THEN 'eight'
WHEN '9' THEN 'nine'
END +' '+CASE
WHEN (@s='0') THEN 'zero'
WHEN (@temp<>'0')AND( ((LEN(@s)-@i) % 3)=2) THEN 'hundred '
ELSE ''
END + CASE
WHEN ((LEN(@s)-@i)=3) THEN 'thousand '
WHEN ((LEN(@s)-@i)=6) THEN 'million '
WHEN ((LEN(@s)-@i)=9) THEN 'billion '
WHEN ((LEN(@s)-@i)=12) THEN 'trillion '
WHEN ((LEN(@s)-@i)=15) THEN 'quadrillion '
WHEN ((LEN(@s)-@i)=18) THEN 'quintillion '
WHEN ((LEN(@s)-@i)=21) THEN 'sextillion '
WHEN ((LEN(@s)-@i)=24) THEN 'septillion '
WHEN ((LEN(@s)-@i)=27) THEN 'octillion '
WHEN ((LEN(@s)-@i)=30) THEN 'nonillion '
WHEN ((LEN(@s)-@i)=33) THEN 'decillion '
WHEN ((LEN(@s)-@i)=36) THEN 'undecillion '
WHEN ((LEN(@s)-@i)=39) THEN 'duodecillion '
WHEN ((LEN(@s)-@i)=42) THEN 'tredecillion '
WHEN ((LEN(@s)-@i)=45) THEN 'quattuordecillion '
WHEN ((LEN(@s)-@i)=48) THEN 'quindecillion '
WHEN ((LEN(@s)-@i)=51) THEN 'sexdecillion '
WHEN ((LEN(@s)-@i)=54) THEN 'septendecillion '
WHEN ((LEN(@s)-@i)=57) THEN 'octodecillion '
WHEN ((LEN(@s)-@i)=60) THEN 'novemdecillion '
ELSE ''
END+ @result
END
SELECT @i=@i-1
END
return REPLACE(@result,' ',' ')
END











GO
SET QUOTED_IDENTIFIER OFF
GO
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER OFF
GO
SET ANSI_NULLS OFF
GO

then  you can call like by sppilitting datetime

select dbo.NUMBERTOWORDS (4)
select dbo.NUMBERTOWORDS (31)
select dbo.NUMBERTOWORDS (2013)

or you can to i like

declare @Student_Birth_Date datetime =getdate();

declare @Student_AgeDay1 nvarchar(100)

declare @Student_AgeMonth1  nvarchar(100)

declare @Student_AgeYear1  nvarchar(100)

declare @Student_Birth_Wordday  nvarchar(100)

declare @Student_Birth_Wordmonth  nvarchar(100)

declare @Student_Birth_Wordyear  nvarchar(100)

declare @Student_Birth_Word  nvarchar(500)

set @Student_AgeDay1=(select DATEPART(DAY,@Student_Birth_Date))
set @Student_AgeMonth1=(select DATEPART(MONTH,@Student_Birth_Date))
set @Student_AgeYear1=(select DATEPART(YEAR,@Student_Birth_Date))
set @Student_Birth_Wordday=dbo.NUMBERTOWORDS (@Student_AgeDay1)
set @Student_Birth_Wordmonth=dbo.NUMBERTOWORDS (@Student_AgeMonth1)
set @Student_Birth_Wordyear=dbo.NUMBERTOWORDS (@Student_AgeYear1)
set @Student_Birth_Word=(@Student_Birth_Wordday+'-'+@Student_Birth_Wordmonth+'-'+@Student_Birth_Wordyear)