Как создать функции в Mysql

Question

Я пытаюсь реализовать эту функцию, которую я нашел в другом посте

CREATE FUNCTION fnNumberToWords(@Number as BIGINT)

RETURNS VARCHAR(1024)

AS

BEGIN

  DECLARE @Below20 TABLE (ID int identity(0,1), Word varchar(32))

  DECLARE @Below100 TABLE (ID int identity(2,1), Word varchar(32))

  INSERT @Below20 (Word) VALUES

                    ( 'Zero'), ('One'),( 'Two' ), ( 'Three'),

                    ( 'Four' ), ( 'Five' ), ( 'Six' ), ( 'Seven' ),

                    ( 'Eight'), ( 'Nine'), ( 'Ten'), ( 'Eleven' ),

                    ( 'Twelve' ), ( 'Thirteen' ), ( 'Fourteen'),

                    ( 'Fifteen' ), ('Sixteen' ), ( 'Seventeen'),

                    ('Eighteen' ), ( 'Nineteen' )

   INSERT @Below100 VALUES ('Twenty'), ('Thirty'),('Forty'), ('Fifty'),

                           ('Sixty'), ('Seventy'), ('Eighty'), ('Ninety')

DECLARE @English varchar(1024) =

(

    SELECT Case

    WHEN @Number = 0 THEN  ''

    WHEN @Number BETWEEN 1 AND 19

    THEN (SELECT Word FROM @Below20 WHERE ID=@Number)

    WHEN @Number BETWEEN 20 AND 99  

    THEN  (SELECT Word FROM @Below100 WHERE ID=@Number/10)+ '-' +

       dbo.fnNumberToWords( @Number % 10)

    WHEN @Number BETWEEN 100 AND 999  

    THEN  (dbo.fnNumberToWords( @Number / 100))+' Hundred '+

     dbo.fnNumberToWords( @Number % 100)

    WHEN @Number BETWEEN 1000 AND 999999  

    THEN  (dbo.fnNumberToWords( @Number / 1000))+' Thousand '+

     dbo.fnNumberToWords( @Number % 1000) 

    WHEN @Number BETWEEN 1000000 AND 999999999  

    THEN  (dbo.fnNumberToWords( @Number / 1000000))+' Million '+

     dbo.fnNumberToWords( @Number % 1000000)

    WHEN @Number BETWEEN 1000000000 AND 999999999999  

    THEN  (dbo.fnNumberToWords( @Number / 1000000000))+' Billion '+

     dbo.fnNumberToWords( @Number % 1000000000)

    WHEN @Number BETWEEN 1000000000000 AND 999999999999999  

    THEN  (dbo.fnNumberToWords( @Number / 1000000000000))+' Trillion '+

     dbo.fnNumberToWords( @Number % 1000000000000)

    WHEN @Number BETWEEN 1000000000000000 AND 999999999999999999  

    THEN  (dbo.fnNumberToWords( @Number / 1000000000000000))+' Quadrillion '+

     dbo.fnNumberToWords( @Number % 1000000000000000)

    WHEN @Number BETWEEN 1000000000000000000 AND 999999999999999999999  

    THEN  (dbo.fnNumberToWords( @Number / 1000000000000000000))+' Quintillion '+

     dbo.fnNumberToWords( @Number % 1000000000000000000)

    ELSE ' INVALID INPUT' END

 )



 SELECT @English = RTRIM(@English)

 SELECT @English = RTRIM(LEFT(@English,len(@English)-1))

             WHERE RIGHT(@English,1)='-'

 RETURN (@English)

 END

 GO

Но в самом начале fnNumberToWords(@Number as BIGINT) Я получил ошибку @Number is not valid at this position, expecting identifier.

И если я пытаюсь что-то вроде fnNumberToWords(numberConv BIGINT) и удалите AS до Begin Я получил ошибку в первом Declare: Declare is not valid at this position for this server version, expecting:

Я новичок с процедурами и функциями магазина в Mysql, и я не знаю, как их создать или почему у меня есть эти ошибки