SELECT (case when convert(sv.[VISDAT_RAW])<'2021-12-31' then 'y' else null end) "第一批"
, sv.[Subject] "Subject name or identifier"
, sv.[StudyEnvSiteNumber] "Site ID"
, sv.[InstanceName] "Folder instance name"
, sv.[SaveTS] "Timestamp of last save in clinical views"
, sv.[VISDAT_RAW] "访视日期 "
FROM project_sv sv
目的是希望在表格最左新增一列,只要访视日期在2021/12/31之前就赋值y,否则就空值,但是一直报错,实在不知道怎么改了QAQ