SQL Server是否真的评估案例表达式中的每个'then'子句？

I'm working with an ItemNumber field in a legacy system that is 99% numbers, but there are a few records that contain letters. The numbers are all padded with leading zeros so I thought I would just cast them as bigint's to solve this problem, but of course it throws an error when it gets to the records with letters in them.I'm working with an ItemNumber field in a legac