Question

I want to convert a varchar(max) column to decimal(10,4).

When I try to use cast or convert I am getting an arithmetic overflow exception. The issue is that the data stored in the varchar column may contain different precisions and different scales. For example, 123456789.1234567′, 1.12345678 or 123456.1234.

For values like 123456.1234 it is converting with out any issue but for other values I am having some problems.

Answer 1

Implemented using Custom Function.
This will check whether the string value can be converted to Decimal safely

CREATE FUNCTION [dbo].[TryParseAsDecimal]
(
    @Value      NVARCHAR(4000)
    ,@Precision INT
    ,@Scale     INT
)

RETURNS BIT
AS
BEGIN

    IF(ISNUMERIC(@Value) =0) BEGIN
        RETURN CAST(0 AS BIT)
    END
    SELECT @Value = REPLACE(@Value,',','') --Removes the comma

    --This function validates only the first part eg '1234567.8901111111'
    --It validates only the values before the '.' ie '1234567.'
    DECLARE @Index          INT
    DECLARE @Part1Length    INT 
    DECLARE @Part1          VARCHAR(4000)   

    SELECT @Index = CHARINDEX('.', @Value, 0)
    IF (@Index>0) BEGIN
        --If decimal places, extract the left part only and cast it to avoid leading zeros (eg.'0000000001' => '1')
        SELECT @Part1 =LEFT(@Value, @Index-1);
        SELECT @Part1=SUBSTRING(@Part1, PATINDEX('%[^0]%', @Part1+'.'), LEN(@Part1));
        SELECT @Part1Length = LEN(@Part1);
    END
    ELSE BEGIN
        SELECT @Part1 =CAST(@Value AS DECIMAL);
        SELECT @Part1Length= LEN(@Part1)
    END 

    IF (@Part1Length > (@Precision-@Scale)) BEGIN
        RETURN CAST(0 AS BIT)
    END

    RETURN CAST(1 AS BIT)

END