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正則匹配 html標題
??? <[hH]([1-9])>.*?</[hH]\1>

數據庫查詢執行順序:
??? from->where->group by->聚集函數->having->order by
??? table level(id,name)
??? select count(*) as cu from level where id>1 group by name desc? having cu>=1 order by id ;


火狐 xpath 取 document dom 值：
??? id('table8')/tbody/tr[6]/td/@valign



數據庫有為空列排放位置:
??? 1.? select name,
??? ??? ??? ??? ?case
??? ??? ??? ??? ???? ??? when name is null then 0
??? ??? ??? ??? ???? ??? else? 1?
??? ??? ??? ??? ?end
??? ??? ??? ??? ??? as is_null
???????? from level
???????? order by is_null? ;
??? 2.select name from level where name is null
?????? union
????? select name from level where name is not null ;

數據庫報表表鏈為空項替換為0
table a (id); values - > 1 ,2 ,3
table b (id,num); -> (1,15),(1,5)
查詢結果為 要為
1??? 20
2??? 0
3??? 0