place condition in the read or in the code?

I am checking if an item has a linked item in the database but cant decide where to put the condition.

option one: place the condition in the database read statement.

select * from item where id = id. 

Option two check afterwards in code.

temp =  select * from item

for(i = 0; i <sizeof(temp); i++;
{
if(id = temp.id)
{do stuff}
}

开发者_开发百科

Is there a significant difference between the two ?

note code sample probably contains tons of errors, is for explanation purpose only.

---

Definitely do it in the database sql statement!

Otherwise you're going to return potentially millions of results just to get one result.

---

Yes. In the first, you're asking the database for a smaller result set, which may require less effort by the database, less network traffic, and less work by your code.

With the second, you're asking to be featured on thedailywtf.