Where子句中条件的执行顺序

Question

I have the following statement with an Or condition. I am looking what would be the result when both conditions are true.

 var result = db.Result.FirstOrDefault(x=>(x.ID==50||x.ID==60)&&x.Name="XYZ");

In a case where I have a row in the result table where both the conditions are true, ie; x.ID=50 and x.ID=60 . What would be the result of the query?

I have already tested to get the result in a test environment. But I wanted to make sure that the order of execution would always remain the same no matter what the size of the database is. As I have read that the where clause uses some sort of indexing for faster retrieval, what would be the course of execution of this statement.

The provided query is just a sample and the name ID has nothing to do with the unique identified of a table.

Question

How would the check be performed on the database? I would expect a result where it first checks if ID ==50 and on failure check if ID==60 . If this is my expected result, would the query given above achieve my task?

Update after answer

I find it necessary to give a more clearer example so that the question is more understandable. (If this update makes the existing answers invalid, I am really sorry)

 var result = db.result.firstordefault(x=>(x.foreignkeyid == someval|| foreignkeyid == 123)&& x.Name=="XYZ");

And my database sample

ID  foreignkeyid    Name
1      123          XYZ
2    somevalue      XYZ
3    anothervalue   XYZ

In this case when the query is executed the result would return the row with ID==1 , but I want row wiht ID==2 to be returned.

Worst case attempt to achieve the result

 var result = new Result();
 result =db.Result.firstordefault(x=>x.ID==somevalue&&x.name==xyz);
 if(result==null)
     var result = db.firstordefault(x=>x.ID ==123&& x.name==xyz);

Answer 1

Given this example of yours:

var result = db.result.firstordefault(x=>(x.foreignkeyid == someval|| foreignkeyid == 123)&& x.Name=="XYZ");

In which you want to prioritize the result where fk = someval (fk: foreign key), you can do the following:

db.set.OrderBy(x => x != someval) // false actually comes before true
      .ThenBy(x => x != val2ndPriority)
      .FirstOrDefault(x => (x.fk == someval ||
                            x.fk == val2ndPriority ||
                            x.fk == leastPriorityVal) &&
                           x.Name == "XYZ");

If you have a lot of "prioritized fk values", or if they are unknown at compile time, you can do:

var orderedEnum = db.set.OrderBy(x => x.Id);
foreach (var fk in fksByPriority)
    orderedEnum = orderedEnum.ThenBy(x => x != fk);
var result = orderedEnum.FirstOrDefault(x => fksByPriority.Contains(x.fk) &&
                                             x.Name == "XYZ");

---

How I would prefer it to look like:

Another different approach would be to get all possibly-relevant records and then run similar logic outside of the DB (your db Linq queries normally run smartly right inside the db):

var results = db.set.Where(x => x.Name == "XYZ" &&
                                fks.Contains(x.fk)).ToArray();
var highestPriorityResult =
    results.OrderBy(x => fksByPriority.IndexOf(x.fk)).FirstOrDefault();

---

On a final note, I wish to say that your problem indicates a possibly flawed design. I can't imagine why you'd have this filtering-with-priority-foreign-key issue.