MAX vs Top 1 - which is better?

Question

I had to review some code, and came across something that someone did, and can\'t think of a reason why my way is better and it probably isn\'t, so, which is better/safer/mo

Answer 1

For the queries to have the same result you would need:

SELECT MAX(a_date) FROM a_table WHERE a_primary_key = 5

SELECT TOP 1 a_date FROM a_table WHERE a_primary_key = 5 ORDER BY a_date DESC

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The best way to know which is faster is to check the query plan and do your benchmarks. There are many factors that would affect the speed, such as table/heap size, etc. And even different versions of the same database may be optimized to favor one query over the other.

Answer 2

1) When there is a clustered index on the table and the column to be queried, both the MAX() operator and the query SELECT TOP 1 will have almost identical performance.

2) When there is no clustered index on the table and the column to be queried, the MAX() operator offers the better performance.

Reference: http://www.johnsansom.com/performance-comparison-of-select-top-1-verses-max/

Answer 3

I ran an experiment and I got the Clustered Index Cost 98% when I used an aggregate like Min/ Max, but when I used TOP and Order By, Clustered Index Scan cost was reduced to 45%. When it comes to querying large datasets, TOP and Order By combination will be less expensive and will give faster results.

Answer 4

They are different queries.

The first one returns many records (the biggest a_date for each event_id found within a_primary_key = 5)

The second one returns one record (the smallest a_date found within a_primary_key = 5).

Answer 5

I perform max and top on one table with 20,00,000+ records , and found that Top give faster result with order by than max or min function.

So , best way is to execute both your query one by one for some time and check connection elapsed time for than.

Answer 6

MAX and TOP function differently. Your first query will return the maximum value found for a_date that has a a_primary_key = 5 for each different event_id found. The second query will simply grab the first a_date with a a_primary_key = 5 found in the result set.