SQL : First condition in OR statement in JOIN is always executed first?

Question

在 SQL Server 中，我有以下设计:

是否 100% 确定 JOIN 中 OR 语句的第一个条件将首先执行？那么下面的SQL语句会得到绿色的结果吗？

SELECT P.Name, D.Percentage
FROM Personnel P
JOIN Department D ON
  P.Dep_Code = D.Code AND
  (P.SubDep_Code = D.SubCode OR D.SubCode = '*')

Answer 1

Is it 100% sure that the first condition from the OR statement in aJOIN will be executed first ?

没有。没有保证的计算顺序，即使整个表达式仍然计算为相同的值，并且不会影响连接中匹配的行。

您的查询将给出以下结果:

Name       Percentage
---------- -----------
P-A        100
P-A        20
P-A        80
P-B        100

我猜您正在寻找类似的东西。

select P.Name,
       coalesce(D1.Percentage, D2.Percentage) as Percentage
from Personnel as P
  left outer join Department as D1
    on P.Dep_Code = D1.Code and
       P.SubDep_Code = D1.SubCode
  left outer join Department as D2
    on P.Dep_Code = D2.Code and
       D2.SubCode = '*'
where coalesce(D1.Percentage, D2.Percentage) is not null

您可以在此处使用 SQL Server 2008 尝试查询。https://data.stackexchange.com/stackoverflow/qt/118492/