How do I pad digits with leading zeros?

Here is one way. Basically, it compares the number of desired digits with the length of the number being padded, and creates that many instances of zero to its left. 
 

<%      Function PadDigits(n, totalDigits)            PadDigits = Right(String(totalDigits,"0") & n, totalDigits)        End Function  %>

 
And in JavaScript: 
 

<script language=javascript runat=server>        function PadDigits(n, totalDigits)      {          n = n.toString();          var pd = '';          if (totalDigits > n.length)          {              for (i=0; i < (totalDigits-n.length); i++)              {                  pd += '0';              }          }          return pd + n.toString();      }    </script>

 
Sample usage: 
 

<%      Response.Write(PadDigits(46,8)) ' returns 00000046      Response.Write(PadDigits(4,5)) ' returns 00004      Response.Write(PadDigits(32,6)) ' returns 000032      Response.Write(PadDigits(22,1)) ' returns 22  %>

 
And here are a couple of methods in T-SQL: 
 

SELECT REPLACE(STR(column, 5), SPACE(1), '0') FROM Table    SELECT RIGHT('00000' + RTRIM(column), 5) FROM Table

 
And here is a technique that can be useful for sorting on a varchar column that might contain numbers (you can't order by CAST AS INT because some values will contain characters): 
 

SELECT column FROM table ORDER BY RIGHT('00000' + RTRIM(column), 5)

 
To see how this can change a query, consider the following example (SQL Server): 
 

SET NOCOUNT ON  CREATE TABLE #foo(bar VARCHAR(5))  INSERT #foo VALUES('1')  INSERT #foo VALUES('2')  INSERT #foo VALUES('9')  INSERT #foo VALUES('10')  INSERT #foo VALUES('20')    -- compare the results of this query:  SELECT bar FROM #foo ORDER BY bar    -- to the results of this query:  SELECT bar FROM #foo ORDER BY RIGHT('00000' + bar, 5)    DROP TABLE #foo