tsql - How to determine the field value which can not convert to (decimal, float,int) in SQL Server

Question

I have a SQL Server database.

One field has values which are like

 ID      VALUE
  1      NEGATIF
  2      11.4
  3      0.2
  4      A RH(+)
  5      -----
  6      >>>>>
  7      5.6<
  8      -13.9

I want to CONVERT VALUE field to decimal, of course convert-able fields.

1. What kind of SQL statement can do this?

2. How can I understand which value is raising error while converting?

PS: I think this can solve WHERE VALUE LIKE '[a-z]' but how can I add more filter like [-+ ()] ?

Answer 1

Plain ISNUMERIC is rubbish

• Empty string, +, - and . are all valid
• So is +. etc
• 1e-3 is valid for float but not decimal (unless you CAST to float then to decimal)

For a particularly cryptic but failsafe solution, append e0 or .0e0 then use ISNUMERIC

SELECT
   ISNUMERIC(MyCOl + 'e0')   --decimal check,
   ISNUMERIC(MyCOl + '.0e0')  --integer check

So

SELECT
    ID, VALUE,
    CAST(
          CASE WHEN ISNUMERIC(VALUE + 'e0') = 1 THEN VALUE ELSE NULL END
          AS decimal(38, 10)
        ) AS ConvertedVALUE
FROM
    Mytable