Efficient ISNUMERIC() replacements on SQL Server?

Question

So I just spent 5 hours troubleshooting a problem which turned out to be due not only to the old unreliable ISNUMERIC but it looks like my problem only appears

Answer 1

For SQL Server 2005 and above.... take advantage of try/catch...

declare @test varchar(10), @num decimal
select @test = '0123A'

begin try
    select @num = cast(@test as decimal)
    print '1'
end try 
begin catch
    print '0'
end catch

prints 0.

Change @test = '01234' or @test = '01234.5' and it prints 1.

Answer 2

Another option might be to write an extended stored procedure in a language such as C, make it into a DLL and make it available to SQL Server.

I don't imagine it would take too many lines of code to do, and it probably would be faster than writing a Managed Stored Procedure in .NET, because you wouldn't incur the extra overheard from loading the CLR.

Here's a tidbit of information: http://msdn.microsoft.com/en-us/library/ms175200.aspx

Here's some C++ code that might work for you:

using namespace std;

int checkNumber() {
  int number = 0;
  cin >> number;
  cin.ignore(numeric_limits<int>::max(), '\n');

  if (!cin || cin.gcount() != 1)
    cout << "Not a number.";
  else
    cout << "Your entered: " << number;
  return 0;
}

Answer 3

Are you ever going to be handling number systems outside of your own (human) language, like Chinese etc? If so, I'd suggest using the libuninum library.

Answer 4

SQL 2012 onwards, you can use TRY_PARSE() function instead of ISNUMERIC().

SELECT
 TRY_PARSE('123' as int) as '123'
,TRY_PARSE('abc' as int) as 'abc'

Answer 5

According to Microsoft support the only efficient way to replace UDF function is to write your own .NET function version.

Of course, if your database admin allows that :).

Mine doesn't :(.

Answer 6

IsNumeric() seems to have problems with spaces, 'D', 'E', dollar signs and all sorts of other characters. What we typically want is something that tells us whether a CAST or CONVERT will succeed. This UDF, while not the fastest solution, has worked very well for me.

create function dbo.udf_IsNumeric(@str varchar(50))
  returns int
as
begin
  declare @rtn int
  select @rtn =
    case
      when ltrim(rtrim(@str)) in('.', '-', '-.', '+', '+.') then 0
      when ltrim(rtrim(@str)) like '%[^-+.0-9]%' then 0
      else isnumeric(@str)
    end
  return @rtn
end