sql charindex extract number from string

I have a column called original_filename which contains text. within the text there is a file ID which I want to extract. The description starts with "error_rows_" as shown below. However the file ID's vary in length i.e 999 to 999999 followed by additional text.

 error_rows_90349_2014-04-10_00-00-00_Transaction-Login_TheHut.gpg
 error_rows_904003_2014-04-10_12-00-00_Transaction-Login_TheHut.gpg
 error_rows_90403_2014-04-10_12-00-00_Transaction-Registration_TheHut.gpg
 error_rows_9060_2014-04-11_00-00-00_Transaction-Login_TheHut.gpg

Can someone help me with the sql to extract this. the end result should be:

90349 904003 90403 9060

I have been trying to use charindex withou success

Solution

Try this:

DECLARE @Test TABLE (TestData VARCHAR(500));
INSERT INTO @Test SELECT 'error_rows_90349_2014-04-10_00-00-00_Transaction-Login_TheHut.gpg';
INSERT INTO @Test SELECT 'error_rows_904003_2014-04-10_12-00-00_Transaction-Login_TheHut.gpg';
INSERT INTO @Test SELECT 'error_rows_90403_2014-04-10_12-00-00_Transaction-Registration_TheHut.gpg';
INSERT INTO @Test SELECT 'error_rows_9060_2014-04-11_00-00-00_Transaction-Login_TheHut.gpg';
SELECT
    *,
    CONVERT(INT, SUBSTRING(TestData, 12, CHARINDEX('_', TestData, 12) - 12))
FROM
    @Test;

Results: