Which is more expensive? For loop or database call?

Question

In general, which is more expensive? A double-nested for loop and one call to a database or a call to a database for each of N items in only one for loop?

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Answer 1

In general, the fewer times you hit the database, the better. There are a number of reasons for this, including:

• The database will be able to optimize better if it can try to fetch everything all at once
• You remove all of the overhead of communicating with the database multiple times, which can be quite significant