even on columns with a low cardinality, an index will stop the SQL engine having to perform a table scan
There is also the issue of statistics
you may have only 4 different values in a column but if 90% are one value, 7% another, 2% the third with the fourth value getting 1%, then the index with statistics will be able to find that 1% a lot faster than without.
- Visitors can check out the Forum FAQ by clicking this link. You have to register before you can post: click the REGISTER link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. View our Forum Privacy Policy.
- Want to receive the latest contracting news and advice straight to your inbox? Sign up to the ContractorUK newsletter here. Every sign up will also be entered into a draw to WIN £100 Amazon vouchers!
Reply to: Non Clustered Index Question
Collapse
You are not logged in or you do not have permission to access this page. This could be due to one of several reasons:
- You are not logged in. If you are already registered, fill in the form below to log in, or follow the "Sign Up" link to register a new account.
- You may not have sufficient privileges to access this page. Are you trying to edit someone else's post, access administrative features or some other privileged system?
- If you are trying to post, the administrator may have disabled your account, or it may be awaiting activation.
Logging in...
Previously on "Non Clustered Index Question"
Collapse
-
Non Clustered Index Question
I was under the impression that a non clustered index hould be created where the query results will be highly selective.
The execution plan for a badly performing query is prompting me to put a nc index on a status field; one that can only have 1 of 5 values. In fact, the clause statusid <> 11 brings back approx 25% of a table containing 300,000 rows.
Suggested index also includes all the other fields in the table but only statusid is in the index.
The optimiser uses the index & the query performs much better.
I just don't get it as it sees to go against all the rules.
Can anyone see what's going on?
This is the query:
SELECT wi.*,wia.*
FROM WorkItem wi
LEFT OUTER JOIN WorkItemAction wia ON wia.WorkItemId = wi.WorkItemId
WHERE wi.StatusId NOT IN (11, 15, 99)
AND wia.statusid <> 11
AND (wi.OwnerTeamMember_TeamMemberId = @teammemberid OR wia.AllocatedTeamMember_TeamMemberId = @teammemberid )
ORDER BY wia.nextactiondate, wi.nextretrydate, wi.priority, wi.currentweighting descTags: None
- Home
- News & Features
- First Timers
- IR35 / S660 / BN66
- Employee Benefit Trusts
- Agency Workers Regulations
- MSC Legislation
- Limited Companies
- Dividends
- Umbrella Company
- VAT / Flat Rate VAT
- Job News & Guides
- Money News & Guides
- Guide to Contracts
- Successful Contracting
- Contracting Overseas
- Contractor Calculators
- MVL
- Contractor Expenses
Advertisers
Contractor Services
CUK News
- Streamline Your Retirement with iSIPP: A Solution for Contractor Pensions Sep 1 09:13
- Making the most of pension lump sums: overview for contractors Sep 1 08:36
- Umbrella company tribunal cases are opening up; are your wages subject to unlawful deductions, too? Aug 31 08:38
- Contractors, relabelling 'labour' as 'services' to appear 'fully contracted out' won't dupe IR35 inspectors Aug 31 08:30
- How often does HMRC check tax returns? Aug 30 08:27
- Work-life balance as an IT contractor: 5 top tips from a tech recruiter Aug 30 08:20
- Autumn Statement 2023 tipped to prioritise mental health, in a boost for UK workplaces Aug 29 08:33
- Final reminder for contractors to respond to the umbrella consultation (closing today) Aug 29 08:09
- Top 5 most in demand cyber security contract roles Aug 25 08:38
- Changes to the right to request flexible working are incoming, but how will contractors be affected? Aug 24 08:25
Leave a comment: