简单三个表之间关联 与 case when语句的应用

case when语句运用

 select b.cur_branch,
 count(p.conttract_id),
 sum(case when p.aff_date is null then p.payable_money else 0 end),
 sum(case when p.aff_date is null and p.fee_item ='租金' then p.payable_money else 0 end),
 sum(case when p.aff_date is null and p.fee_item ='电费' then p.payable_money else 0 end),
 sum(case when p.aff_date is not null then 1 else 0 end),
 sum(case when p.aff_date is null then 1 else 0 end)
 from WG_PJHSB p, wg_jzmb b
 where p.station_id = b.station_code
 group by b.cur_branch
 order by b.cur_branch

运用1：sum（case when p.aff_date is null then p.payable_money else 0 end）

累加票据金额

运用2：sum(case when 条件语句l then 1 else 0 end)

累加计数使用。