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

Question

In SQL Server, I've the following design:

Is it 100% sure that the first condition from the OR statement in a JOIN will be executed first ? So that the following SQL statement will result in the green result?

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 a JOIN will be executed first ?

No. There is no guaranteed order of evaluation and even if there where the entire expression would still evaluate to the same value and would not influence what rows are matched in the join.

Your query will give this result:

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

I guess you are looking for something like this.

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

You can try the queries here using SQL Server 2008. https://data.stackexchange.com/stackoverflow/qt/118492/