Eliminate Clustered Index Scan in query

Question

I have this query involving 2 tables joined.

Select  q.id, 
                         q.LastUpdatedTicksSinceEpoch,
                            q.[Type] [QuoteType],
       q.LatestFormData [FormDataJson], 
                            q.QuoteNumber, 
                            q.QuoteState,
       q.policyId,
                            p.CustomerId, 
                            p.CustomerFullName, 
                            p.CustomerAlternativeEmail,
                            p.CustomerHomePhone,
                            p.CustomerMobilePhone,
                            p.CustomerWorkPhone,
                            p.CustomerPreferredName,
       p.ProductId
                            from Quotes q
                    INNER JOIN  PolicyReadModels p on q.PolicyId=p.id
                    where
                            p.TenantId = @TenantId
                            and p.Environment = @Environment
                           and q.LastUpdatedTicksSinceEpoch > @LastUpdatedTicksSinceEpoch
         and q.QuoteState <> 'Nascent'
                            and q.QuoteNumber is not null
                            and q.IsDiscarded = 0
     ORDER BY q.LastUpdatedTicksSinceEpoch

When I run it and get the execution plan, I see Clustered Index Scan - which I want to Eliminate and use an Index Seek.

How can I eliminate the clustered index scan here? How can I construct a new INDEX? To add more context to this, this will query will be called by 12 parallel thread(12 connections), so I need this fast and optimized.

Here is my Query and execution plan:

https://www.brentozar.com/pastetheplan/?id=HkWjdvKDD

Answer 1

Create an index on:

create index someIndex on
Quotes (LastUpdatedTicksSinceEpoch)
include (Id, Type, LatestFormData, QuoteNumber, QuoteState, PolicyId, IsDiscarded)
where IsDiscarded = 0
                      

Answer 2

This

• Filters by your two fixed values (QuoteNumber NOT NULL and IsDiscarded = 0)
• Sorts the data by LastUpdatedTicksSinceEpoch (as you are passing a variable to that in your WHERE clause, and it appears the most likely one you want to sort on
• Includes all other relevant fields so doesn't need to go back to the clustered index (eg, becomes a covering index).

Note that quote.ID is not included as it is your PK (from what I can tell in the execution plan) and therefore implicitly included in the index. You can include it though - no harm done at all (eg, index size and performance will be exactly the same).

CREATE INDEX IX_q ON Quotes 
    (
    LastUpdatedTicksSinceEpoch
    )
INCLUDE
    (
    PolicyId,
    [Type],
    QuoteState,
    LatestFormData,
    QuoteNumber,
    IsDiscarded
    )
WHERE 
    (
    QuoteNumber is not null 
    AND IsDiscarded = 0
    )

Note: I think this is probably the fastest you can get, but you need to be careful because more indexes on table mean slower inserts, updates and deletes.

Often I find a much shorter index that can be used in many places is preferable to a very specific index like this (remember, if some fields like LatestFormData are large, then this index can get bloated and not be as useful to other queries).