Question

EDIT: I have added ‘Slug’ column to address performance issues on specific record selection.

I have following columns in my table.

Id Int - Primary key (identity, clustered by default) Slug varchar(100) ... EntryDate DateTime 

Most of the time, I’m ordering the select statement by EntryDate like below.

Select T.Id, T.Slug, ..., T.EntryDate From (     Select Id, Slug, ..., EntryDate,           Row_Number() Over (Order By EntryDate Desc, Id Desc) AS RowNum     From TableName     Where ... ) As T Where T.RowNum Between ... And ... 

I’m ordering it by EntryDate and Id in case there are duplicate EntryDates.

When I’m selecting A record, I do the following.

Select Id, Slug, ..., EntryDate From TableName Where Slug = @slug And Year(EntryDate) = @entryYear      And Month(EntryDate) = @entryMonth 

I have a unique key of Slug & EntryDate.

What would be a smart choice of keys and indexes in my situation? I’m facing performance issues probably because I’m ordering by a column that is not clustered indexed.

Should I have Id set as non-clustered primary key and EntryDate as clustered index?

I appreciate all your help. Thanks.

EDIT:

I haven’t tried adding non-clustered index on the EntryDate. Data inserted from back-end, so performance for insert isn’t a big deal for me. Also, EntryDate is not always the date when it is inserted. It can be a past date. Back-end user picks the date.

Answer 1

Based on the current table layout you want some indexes like this.

CREATE INDEX IX_YourTable_1 ON dbo.YourTable (EntryDate, Id) INCLUDE (SLug) WITH (FILLFACTOR=90)  CREATE INDEX IX_YourTable_2 ON dbo.YourTable (EntryDate, Slug) INCLUDE (Id) WITH (FILLFACTOR=80) 

Add any other columns you are returning to the INCLUDE line.

Change your second query to something like this.

Select Id, Slug, ..., EntryDate From TableName Where Slug = @slug      AND EntryDate BETWEEN CAST(CAST(@EntryYear AS VARCHAR(4) + CAST(@EntryMonth AS VARCHAR(2)) + '01' AS DATE) AND DATEADD(mm, 1, CAST(CAST(@EntryYear AS VARCHAR(4) + CAST(@EntryMonth AS VARCHAR(2)) + '01' AS DATE)) 

The way your second query is currently written the index will never be used. If you can change the Slug column to a related table it will increase your performance and decrease your storage requirements.