Question

我一直在努力工作几个小时，看起来非常简单的查询让我（非常）疯狂。我有2张桌子：

产品

Code    Var
AAI85CLASS2000              9005N
AAI85CLASS2000              9005P

时报

Code            Var     Time
AAI85CLASS2000  NULL    8,68
AAI85CLASS2000  CROM    9,68
AAI85CLASS2000  9005N   19,68

结果我想得到

Code                        Var     Time
AAI85CLASS2000              9005N   19,68
AAI85CLASS2000              9005P   8,68

当存在匹配的Var时，应考虑具体的时间。当没有匹配的Var时，应考虑通用时间（其中Var为NULL）。我请求帮助。感谢。

Answer 1

试试这个：

Select i.code, i.var, case when max(t.var) is not null then max(case when t.var is not null then t.time end) else max(t.time) end time
From items i left join times t
On i.code = t.code and (i.var = t.var or t.var is null)
Group by i.code, i.var;

Answer 2

以下是使用Outer Join

的一种方法

SELECT a.Code,
       a.Var,
       COALESCE(b.time, c.time)
FROM   Items a
       LEFT JOIN Times b
              ON a.Code = b.Code
                 AND a.Var = b.Var
       LEFT JOIN Times c
              ON ( a.Code = b.Code
                   AND a.Var = c.Var
                   AND b.Var IS NULL ) -- To find the non matching var's in previous join
                  OR c.Var IS NULL  -- To find the time from var which is NULL

Live Demo

Answer 3

这是一种方法：

SELECT  I.Code, 
        I.Var, 
        ISNULL(T.Time, (SELECT Time FROM Times WHERE Var IS NULL AND Code = I.Code)) Time
FROM Items I
LEFT JOIN Times T ON I.Code = T.Code AND I.Var = T.Var

对于看起来非常简单的SQL查询需要帮助

3 个答案: