C# SQL Server - More Efficient for Multiple Database accesses or multiple loops through data?

Question

In part of my application I have to get the last ID of a table where a condition is met For example:

SELECT(MAX) ID FROM TABLE WHERE Num = 2

So I can either grab the whole table and loop through it looking for Num = 2, or I can grab the data from the table where Num = 2. In the latter, I know the last item will be the MAX ID.

Either way, I have to do this around 50 times...so would it be more efficient grabbing all the data and looping through the list of data looking for a specific condition...

Or would it be better to grab the data several times based on the condition..where I know the last item in the list will be the max id

I have 6 conditions I will have to base the queries on

Im just wondering which is more efficient...looping through a list of around 3500 items several times, or hitting the database several times where I can already have the data broken down like I need it

Answer 1

I could speak for SqlServer. If you create a StoredProcedure where Num is a parameter that you pass, you will get the best performance due to its optimization engine on execution plan of the stored procedure. Of course an Index on that field is mandatory.

Answer 2

让数据库完成这项工作，这就是它的目的。

Answer 3

Does this table have a high insert frequency? Does it have a high update frequency, specifically on the column that you're applying the MAX function to? If the answer is no, you might consider adding an IS_MAX BIT column and set it using an insert trigger. That way, the row you want is essentially cached, and it's trivial to look up.