Question

I have a SQLite table as

CREATE TABLE T(
    CategoryCode NVARCHAR(64) NOT NULL,
    DateTime     DateTime NOT NULL,
    ItemCode     NVARCHAR(64) NOT NULL,
    ItemName     NVARCHAR(64) NOT NULL,
    ItemValue    NUMERIC(28, 4) NOT NULL
)

The question is how to optimize indexes for the following query:

SELECT
 CategoryCode
,ItemCode
,ItemName
,SUM(ItemValue) as TotalValue
FROM T
WHERE CategoryCode = 'Code1' 
AND DateTime < '2012-01-04 00:00:00'
GROUP BY ItemCode

Thank you!

Answer 1

For the exact query, you will need an index on T(CategoryCode, DateTime) or T(DateTime, CategoryCode), depending on which column is more selective than the other.

However, it is unwise to create an index for a single query without a more holistic view on all access to the table.

e.g. You may find, for example, that if most data in the table has CategoryCode = 'Code1' then the index should only be created on the DateTime column.