SQL Select Command to do a partial match

I need a SQL Select command that can to do a partial match. I need match the first a NBR to the first 10 digits of another number. For example:

ItemID= 10 digits long
EAN11 = 11 digits long.

I need to match STEPUPC.ItemID to the first 10 digits of the SAPMATUPC.EAN11.

SELECT *
FROM STEPUPC
WHERE NOT EXISTS
(SELECT SAPMATUPC.EAN11
FROM SAPMATUPC WHERE STEPUPC.ItemID = SAPMATUPC.EAN11