1.保留小数点。保留小数点，round运算时，必须加 ::numeric
select round(b.num::numeric/b.counts::numeric,4)
2.转日期格式
to_char(t.create_time, 'yyyy')
3.选择语句
case when use_money is not null and download_count is null then -1 else round(use_money::numeric/download_count::numeric,2) end
case when use_money is not null then -1 else xx end