Slight fix to the code

use tempdb;

go

SELECT OrderNo

, CHARINDEX('-',OrderNo,4) AS FindDash

, CASE WHEN LEFT(OrderNo,CHARINDEX('-',OrderNo,4)) =''

THEN OrderNo

ELSE LEFT(OrderNo,CHARINDEX('-',OrderNo,4))

END AS NoSuffix

FROM (

SELECT 'SO-123456' AS OrderNo

UNION ALL

SELECT 'SO-123456-01'

UNION ALL

SELECT 'SO-123456-2'

UNION ALL

SELECT 'SO-123457'

UNION ALL

SELECT 'SO-123457-1'

UNION ALL

SELECT 'SO-123457-02'

UNION ALL

SELECT 'SO-123458') x