You need CHARINDEX() to find the position of the second dash (if it exists).

This almost works:

use tempdb;

go

SELECT OrderNo

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

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

If you set up your question so that people can answer it really easily, (by providing readily consumable code/SELECT statements), you'll get more answers, because people won't have to work as hard to solve your problem. I usually find that setting up the question properly gets me most of the way to the answer too.

HTH,

Pieter