PostgreSQL的case when

select tt.dict_label as display_item,t1.ratio from
 (select t.product_level,round(sum(case when t.detect_result=‘2‘ then 1 else 0 end)::NUMERIC/count(1)::NUMERIC,4) as ratio
from t_detect_record t
where t.district=‘3‘  and t.e_commerce_platform=‘3‘
group by t.product_level) t1
  left join t_dict tt on t1.product_level=tt.dict_value
where tt.dict_type=‘product_level‘

select country, sum( case when sex = ‘1‘ then   population else 0 end),  --男性人口

 sum( case when sex = ‘2‘ then  population else 0 end)   --女性人口

from table_a   group by country;

PostgreSQL的case when

原文：http://www.cnblogs.com/esther-qing/p/5908955.html