sql查询里怎么实现sumIf()功能？比如说基于逐笔成交的数据，根据买卖标志位统计买、卖量。
我尝试如下查询写法失败
date=2020.12.25
time=14:30:00
select sum(TrdMoney) as amount,sum(Volume * iif(TrdBSFlag=='S',1,0)) as sellVolume, ,sum(Volume * iif(TrdBSFlag=='B',1,0)) as buyVolume from loadTable("dfs://level2","ticktrade_sh") where TradeDate=date and UpdateTime between temporalAdd(time,-3,'m'):time group by SecurityID
