[英]Left Outer Join With Per Group of Right table?
我有兩個表L和R
L
R
我想在L與R每組行之間建立一個Left Outer join 。
Left Outer join
更清楚的是,左表中的所有行都必須位於每組右行的結果集中。
SQL中最好的查詢是什么?
我用CROSS JOIN運算符解決。
CROSS JOIN
表L:
表R:
我的查詢:聲明@userid int set @userid = null
SELECT T.Id, T.Name,T.UserId,R.Val FROM ( SELECT L.Id, L.Name,R.UserId FROM (SELECT DISTINCT UserId FROM R ) R CROSS JOIN L )T LEFT OUTER JOIN R ON (T.Id = R.DayId AND T.UserId = R.UserId) where @userid is null or T.userid=@userid
結果:
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