sql - 以半月分组

SELECT siteNumber [站点],
CONVERT(VARCHAR(7),day,120)+‘-‘+
case when day(day) between 1 and 15 then ‘上半月‘ else ‘下半月‘ end [半月],
SUM(rainVal) [半月降雨量]
FROM r a
GROUP BY CONVERT(VARCHAR(7),day,120)+‘-‘+
case when day(day) between 1 and 15 then ‘上半月‘ else ‘下半月‘ end,
siteNumber 
order by siteNumber, CONVERT(VARCHAR(7),day,120)+‘-‘+
case when day(day) between 1 and 15 then ‘上半月‘ else ‘下半月‘ end