1.累加力扣534：关键点：sum(games_played)over(partitionbyplayer_idorderbyevent_date)--滑动累加求和，指向性明显，用sum()...over()...窗口函数。注：orderby后

有时我们会对三个表做连接。力扣180：selectdistinctl1.NumasConsecutiveNumsfromLogsl1,Logsl2,Logsl3wherel1.Num=l2.Numandl1.Num=l3.Numandl1.Id

对于较复杂的题，按需求处理产生新表，再连接。力扣1126：selectbusiness_idfromEventsjoin(selectevent_type,avg(occurences)asavg_occurencesfromEvents