Performance for Avg & Max in SQL

I want to decrease the query execution time for the following query. This query is taking around 1 min 20 secs for about 2k records.

Numbers of records in table: 1348474

Number of records processed through where query: 25000

Number of records returned: 2152

SELECT Col1, Col2,
ISNULL(AVG(Col3),0) AS AvgCol,
ISNULL(MAX(Col3),0) AS MaxCol,
COUNT(*) AS Col5
FROM TableName WITH(NOLOCK)
GROUP BY Col1, Col2
ORDER BY Col1, MaxCol DESC

I tried removing the AVG & MAX columns and it lowered to 1 sec. Is there any optimized solution for the same? I have no other indexing other than Primary key.

Update

Indexes added: nonclustered located on PRIMARY – Col1

nonclustered located on PRIMARY – Col2

clustered, unique, primary key located on PRIMARY – Id

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Thanks in advance..Happy coding !!!

Answer

For this query:

SELECT Col1, Col2,
       COALESCE(AVG(Col3), 0) AS AvgCol,
       COALESCE(MAX(Col3), 0) AS MaxCol,
       COUNT(*) AS Col5
FROM TableName
GROUP BY Col1, Col2
ORDER BY Col1, MaxCol DESC;

I would start with an index on (Col1, Col2, Col3).

I’m not sure if this will help. It is possible that the issue is the time for ordering the results.