Does order of conditions under where clause in a LINQ query matter

Question

I am new to LINQ. Could anyone please clarify whether the order of conditions under where clause in a LINQ query matter.

for eg: Is there any difference w.r.t performance between below two queries

Query-1

from prod in Products 
where prod.ExpiryDate == Products.Where(s => s.ID.Equals(CurrObj.Id) && 
      s.Type.Equals(CurrObj.Type)).Max(s => s.ExpiryDate) && 
      prod.ID.Equals(CurrObj.Id) && prod.Type.Equals(CurrObj.Type) 
select new
{
   AmountFrom = prod.AmountFrom,
   AmountTo = prod.AmountTo
}

Query-2

from prod in Products 
where prod.ID.Equals(CurrObj.Id) && 
      prod.Type.Equals(CurrObj.Type) &&
      prod.ExpiryDate == Products.Where(s => s.ID.Equals(CurrObj.Id) && s.Type.Equals(CurrObj.Type)).Max(s => s.ExpiryDate)
select new
{
    AmountFrom = prod.AmountFrom,
    AmountTo = prod.AmountTo
}

Edit: I just measured the performance. Query-1 takes around 900ms whereas Query-2 takes 350ms.

Answer 1

If it's LINQ-To-Objects it matters.

Enumerable.Where is comparable to an ifclause. So this ...

if(expensiveMethodThatReturnsBool() && num1 < num2)
{
    // ...
}

... is probably less efficient than:

if(num1 < num2 && expensiveMethodThatReturnsBool())
{
    // ...
}

because && is a short-circuit operator. The second expression is evaluated only if the first returned true. The same applies to ||, the second is evaluated only if the first returned false.

7.11 Conditional logical operators

---

It's similar with chained Wheres. Similar because predicates are applied to every remaining item which passed through the previous Where.

So this...

.Where(x => expensiveMethodThatReturnsBool(x))
.Where(x => x.num1 < x.num2)

can also be less efficient than:

.Where(x => x.num1 < x.num2)
.Where(x => expensiveMethodThatReturnsBool(x))

The first is logically equivalent to:

.Where(x => expensiveMethodThatReturnsBool(x) && x.num1 < x.num2)

Answer 2

Well consider it yes, as all thos generated as SQL at the end the two different sql statements will be different, now in certain situations order of things in sql matter, but you cant tell for sure unless you measure it.

I suggest to noy worry about that until you face or know something for sure upon measuring performance.