sql中的case when 语法

case when substring([CertificationNo],1,2)='GI' then 'GIA' when substring([CertificationNo],1,2)='IG' then 'IGI' when substring([CertificationNo],1,2)='HR' then 'HRD' when substring([CertificationNo],1,2)='20' then 'NGGC' when substring([CertificationNo],1,2)='H0' then 'NGTC' else '其他国证' endas [CertType]