TSQL - replace isnumeric = 0 - tsql

Question

I have a select statement and in that select statement I have a few columns on which I perform basic calculations (e.g. [Col1] * 3.14). However, occasionally I run into non-numeric values and when that happens, the whole stored procedure fails because of one row.
I've thought about using a WHERE ISNUMERIC(Col1) <> 0, but then I would be excluding information in the other columns.
Is there a way in TSQL to somehow replace all stings with NULL or 0??

Answer 1

Something like...
SELECT blah1, blah2, blah3
CASE WHEN ISNUMERIC(Col1) = 1 THEN [Col1] * 3.14 ELSE NULL END as whatever
FROM your_table
A case can also be made that..
The non-numeric values should be converted to numeric or NULL if that's what's expected in the column, and
If numbers are expected then the column should be a numeric data type in the first place and not a character data type, which allows for these types of errors.

Answer 2

I prefer Try_Cast:
SELECT
someValue
,TRY_CAST(someValue as int) * 3.14 AS TRY_CAST_to_int
,TRY_CAST(someValue as decimal) * 3.14 AS TRY_CAST_to_decimal
,IIF(ISNUMERIC(someValue) = 1, someValue, null) * 3.14 as IIF_IS_NUMERIC
FROM (values
( 'asdf'),
( '2' ),
( '1.55')
) s(someValue)

Answer 3

ISNUMERIC is a terrible way to do this, as there are far too many things that identify as NUMERIC which are not able to be multiplied by a non-MONEY data type.
https://www.brentozar.com/archive/2018/02/fifteen-things-hate-isnumeric/
This fails miserably, as '-' is a numeric...
DECLARE #example TABLE (numerics VARCHAR(10));
INSERT INTO #example VALUES ('-')
SELECT CASE WHEN ISNUMERIC(numerics) = 1 THEN numerics * 3.14 ELSE NULL END
FROM #example;
Try TRY_CAST instead (albeit amend your DECIMAL precision to suit your needs):
DECLARE #example TABLE (numerics VARCHAR(10));
INSERT INTO #example VALUES ('-')
SELECT TRY_CAST(numerics AS decimal(10,2)) * 3.14 FROM #example;

Answer 4

trycast will test for a specfic type
declare #T table (num varchar(20));
insert into #T values ('12'), ('3.14'), ('5.6E12'), ('$120'), ('-'), (''), ('cc'), ('aa'), ('bb'), ('1/5');
select t.num, ISNUMERIC(t.num) as isnumeric
, isnull(TRY_CONVERT(smallmoney, t.num), 0) as smallmoney
, TRY_CONVERT(float, t.num) as float
, TRY_CONVERT(decimal(18,4), t.num) as decimal
, isnull(TRY_CONVERT(smallmoney, t.num), TRY_CONVERT(float, t.num)) as mix
from #T t
num isnumeric smallmoney float decimal
-------------------- ----------- --------------------- ---------------------- ---------------------------------------
12 1 12.00 12 12.0000
3.14 1 3.14 3.14 3.1400
5.6E12 1 0.00 5600000000000 NULL
$120 1 120.00 NULL NULL
- 1 0.00 NULL NULL
0 0.00 0 NULL
cc 0 0.00 NULL NULL
aa 0 0.00 NULL NULL
bb 0 0.00 NULL NULL
1/5 0 0.00 NULL NULL
interesting the last still fails