CASE WHEN condition THEN result
  [WHEN ...]
  [ELSE result]
 END

select * from city

select SUM(city_id),case name 
when '北京' then '古都'
when '西安' THEN '古都'
when '上海' THEN '魔都'
when 'NewYork' then '紐約'
else '其他城市' END
from city 
GROUP BY 
case name 
when '北京' then '古都'
when '西安' THEN '古都'
when '上海' THEN '魔都'
when 'NewYork' then '紐約'
else '其他城市' END

select sum(city_id),CASE 
when city_id < 3 then '小于3'
when city_id > 8 then '大于8'
else '大于3小于8' END
FROM city
group by
CASE 
when city_id < 3 then '小于3'
when city_id > 8 then '大于8'
else '大于3小于8' END
order by
CASE 
when city_id < 3 then '小于3'
when city_id > 8 then '大于8'
else '大于3小于8' END DESC

(
    case
    when substr(starttime::varchar,0,5)='2020' then '2020年'
    when substr(starttime::varchar,0,5)='2019' then '2019年'
    when substr(starttime::varchar,0,5)='2018' then '2018年'
    when substr(starttime::varchar,0,5)='2017' then '2017年'
    when substr(starttime::varchar,0,5)='2016' then '2016年'
    when substr(starttime::varchar,0,5)='2015' then '2015年'
    when substr(starttime::varchar,0,5)='2014' then '2014年'
    when substr(starttime::varchar,0,5)='2013' then '2013年'
    when substr(starttime::varchar,0,5)='2012' then '2012年'
    when substr(starttime::varchar,0,5)='2011' then '2011年'
    when substr(starttime::varchar,0,5)='2010' then '2010年'
    when starttime is null then '其他年份' end
 ) AS year

<if test="geojsonString !=null and geojsonString !=''">
      WHERE
      st_intersects(geom,st_geomfromgeojson(#{geojsonString}))
</if>