SQL流水帐号的生成

create   proc  aaa
(
         @StockName   varchar ( 50 ),
         @StockCount   int ,
         @StockPrice   money
)
as
     declare   @StockID   varchar ( 10 );
     declare   @num   int ;
     select   @num   =   MAX ( cast ( substring (StockID, 4 , 7 )  as   int ))  from  stock
     if   @num   is   null
     begin
         set   @StockID   =   ' ST- '   +   ' 0000001 '
         insert   into  stock  values ( @StockID , @StockName , @StockCount , @StockPrice )
     end
     else
     begin
         set   @num   =   @num   +   1
         set   @StockID   =   ' ST- '   +   right ( ' 0000000 '   +   replace ( cast ( @num   as   char ( 7 )), '   ' , '' ), 7 )
         insert   into  stock  values ( @StockID , @StockName , @StockCount , @StockPrice )
     end