What Is Table Scan, Index Scan And Index Seek??
Sep 21, 2007Hi,
I want to know wht is a
TABLE SCAN
INDEX SCAN
INDEX SEEKand When they are used, Wht is the difference between all these.????
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Index Seek, Index Scan, Table Scan
Oct 4, 2007
Hey,
what is the difference between Table Scan und Index Scan?
I find no difitions in the internet
Finchen
Difference Between Index Seek && Index Scan && Index Lookup Operations?
Oct 20, 2006please explain the differences btween this logical & phisicall operations that we can see therir graphical icons in execution plan tab in Management Studio
thank you in advance
Index Seek Vs Scan
Nov 4, 2002I have created a nolock view off a table to prevent locks. I have users coming in through MS Access that have switched their queries to run against the views. Now we are noticing that queries that used to run as a clustered index seek against the table are running as a clustered index scan against the table and performance in the queries has dropped.
Is there any way that the same query that hits the view instead of the table can be made to run faster or at least use the index seek?
Thanks,
Steve
What Is The Difference Between Clustered Index Scan And Table Scan
Jan 29, 2006How can I improve performance of my search if I am looking in a table with more than ten million rows with a "like query"?
Does putting an index mean only telling the computer to start in a particular order?
if I index all the coloums does my search get faster ?
how can I decide on an indexing strategy?
Index Scan Vs Index Seek
Mar 1, 2004I have a really strange problem.
I execute this query:
declare @cid int
set @cid = 2003227
select * from sales s, product p where p.product_Id = s.product_Id and customer_id = @cid
select * from sales s, product p where p.product_Id = s.product_Id and customer_id = @cid or @cid = 0
3 Million rows in sales, 120000 in product.
The first does and index seek, the second an index scan.
The execution plan reports that the scan takes 99.87% of the cost, and the seek takes 0.13%
This problem obviously gets worse the bigger the dataset / query /etc.
The reason I query this, is because it never used to take this long to do index scans. Is there something i can change, something i can fix?
Any help would be appreciated.
Josh
Simple Query Chooses Clustered Index Scan Instead Of Clustered Index Seek
Nov 14, 2006the query:
SELECT a.AssetGuid, a.Name, a.LocationGuid
FROM Asset a WHERE a.AssociationGuid IN (
SELECT ada.DataAssociationGuid FROM AssociationDataAssociation ada
WHERE ada.AssociationGuid = '568B40AD-5133-4237-9F3C-F8EA9D472662')
takes 30-60 seconds to run on my machine, due to a clustered index scan on our an index on asset [about half a million rows]. For this particular association less than 50 rows are returned.
expanding the inner select into a list of guids the query runs instantly:
SELECT a.AssetGuid, a.Name, a.LocationGuid
FROM Asset a WHERE a.AssociationGuid IN (
'0F9C1654-9FAC-45FC-9997-5EBDAD21A4B4',
'52C616C0-C4C5-45F4-B691-7FA83462CA34',
'C95A6669-D6D1-460A-BC2F-C0F6756A234D')
It runs instantly because of doing a clustered index seek [on the same index as the previous query] instead of a scan. The index in question IX_Asset_AssociationGuid is a nonclustered index on Asset.AssociationGuid.
The tables involved:
Asset, represents an asset. Primary key is AssetGuid, there is an index/FK on Asset.AssociationGuid. The asset table has 28 columns or so...
Association, kind of like a place, associations exist in a tree where one association can contain any number of child associations. Each association has a ParentAssociationGuid pointing to its parent. Only leaf associations contain assets.
AssociationDataAssociation, a table consisting of two columns, AssociationGuid, DataAssociationGuid. This is a table used to quickly find leaf associations [DataAssociationGuid] beneath a particular association [AssociationGuid]. In the above case the inner select () returns 3 rows.
I'd include .sqlplan files or screenshots, but I don't see a way to attach them.
I understand I can specify to use the index manually [and this also runs instantly], but for such a simple query it is peculiar it is necesscary. This is the query with the index specified manually:
SELECT a.AssetGuid, a.Name, a.LocationGuid
FROM Asset a WITH (INDEX (IX_Asset_AssociationGuid)) WHERE
a.AssociationGuid IN (
SELECT ada.DataAssociationGuid FROM AssociationDataAssociation ada
WHERE ada.AssociationGuid = '568B40AD-5133-4237-9F3C-F8EA9D472662')
To repeat/clarify my question, why might this not be doing a clustered index seek with the first query?
SUM Uses Table Scan But Not Index
Jan 16, 2002Hi I'm issuing a SELECT on a field with the SUM on SQL Server 7. I have an index on the field in the WHERE clause but upon analysis, the Query Optimizer always uses a Full Table Scan. Can anyone explain why and is there a way to use the index.
HEre's the structure:
SELECT SUM(colA)
FROM TABLE tblB
GROUP BY colC
An index exists on column colC.
Thanks
Index Help To Avoid Table Scan
Sep 29, 2006I have following query to delete the data from fact history table based on fact table. logid, level and post_date uniquely identify the rows on both fact and history table. I want to create indexes on the joined columns.I tried with clustered index (logid, level and post_date) it gives clustered index scan. I also tried with non clustered indexes on each column (logid, level and post_date) but still getting table scan.
Do you have any suggestion on which columns should I create proper indexes to avoid table or index scan? There are about 6 million rows on each table.
DELETE xbar_fact_history
FROM xbar_fact_history AS a
INNER JOIN xbar_fact AS b
ON a.logid = b.logid
AND a.level = b.level
AND a.post_date = b.post_date
AND a.check_CheckSum <> BINARY_CHECKSUM(b.out_mins,b.nor_hrs,b.pdi_call)
______________________________________________________________
Thanks
Sanjeev
SQL 2012 :: 5 Columns In Table - Clustered Index Scan
Mar 28, 2014I have a table with clustered index on that. I have only 5 columns in that table. Execution plan is showing that Index scan occurred. What are the cause of the Index scan how can we change that to index seek?
I am giving that kind of similar query below
SELECT @ProductID= ProductID FROM Product WITH (NOLOCK) WHERE SalesID= '@salesId' and Product = 'Clothes '
SQL Server 2014 :: Memory-optimized Queries Using Table Scan Instead Of Seek?
Sep 19, 2015I've been having some trouble getting a single-column "varchar(5)" field to reliably use a table seek instead of a table scan. The production table in this case contains 25 million rows. As impressive as it is to scan 25 million rows in 35 seconds, the query should run much faster.
Here's a partial table description:
CREATE TABLE [dbo].[Summaries_MO]
(
[SummaryId] [int] IDENTITY(1,1) NOT NULL,
[zipcode] [char](5) COLLATE Latin1_General_100_BIN2 NOT NULL,
[Golf] [bit] NULL,
[Homeowner] [bit] NULL,
[Code] .....
Typically, this table is accessed with a query that includes:
SELECT ...
FROM SummaryTable
WHERE ixZIP IN (SELECT ZipCode FROM @ZipCodesForMO)
This query insists on using a table scan. I've tried WITH (FORCESEEK) for example, but that just makes the query fail.
As I've investigated this issue I also tried:
SELECT * FROM Summaries WHERE ZipCode IN ('xxxxx', 'xxxxx', 'xxxxx')
When I run this query with 64 or fewer (actual, valid) ZIP codes, the query uses a table seek.But when I give it 65 or more ZIP codes it uses a table scan.
To summarize, the production query always uses a table scan, and when I specify 65 or more ZIP codes the query also uses a table scan. I'm wondering if the data type of the indexed column (Latin1_General_100_BIN2) is somehow the problem. I'll likely try converting the ZIP codes to an integer to see what happens.
Clustered Index Scan
Apr 8, 2008I am running a SELECT on a table. This READ operation ends up going through Clustered Index Scan. I want to know whether Clustered Index Scan , blocks other concurrent transactions trying to INSERT into this table? Does Clustered Index Scan locks the entire clustered index?
View 3 Replies View RelatedAvoid Index Scan With LIKE And A Variable
Jul 23, 2005Hi,Here's my problem: I want to write a stored procedure that returns allrecords from a table that have a certain column starting with giventext. I however find that using LIKE and a variable always causes anindex scan... which is causing performance issues. My table has about3.5M records.Below is a test. In query analyser if I look at the execution plan forthe following it will come up as in index scan. However, if i justhard-code the text it all works fine (index seek).How can I do this with reasonable speed???Thanks GregDECLARE @find varchar(50)SET @find = 'start'SELECT TOP 100*FROM TestWHERECol1 LIKE @find + '%'--Col1 LIKE 'start%'
View 1 Replies View RelatedIF NOT EXISTS (... - EXISTS TABLE : Nested Iteration. Table Scan.Forward Scan.
Sep 20, 2006Hi,
This is on Sybase but I'm guessing that the same situation would happen on SQL Server. (Please confirm if you know).
I'm looking at these new databases and I'm seeing code similar to this all over the place:
if not exists (select 1 from dbo.t1 where f1 = @p1)
begin
select @errno = @errno | 1
end
There's a unique clustered in dex on t1.f1.
The execution plan shows this for this statement:
FROM TABLE
dbo.t1
EXISTS TABLE : nested iteration.
Table Scan.
Forward scan.
Positioning at start of table.
It's not using my index!!!!!
It seems to be the case with EXISTS statements. Can anybody confirm?
I also hinted to use the index but it still didn't use it.
If the existence check really doesn't use the index, what's a good code alternative to this check?
I did this and it's working great but I wonder if there's a better alternative. I don't really like doing the SET ROWCOUNT 1 and then SET ROWCOUNT 0 thing. SELECT TOP 1 won't work on Sybase, :-(.
SET ROWCOUNT 1
SELECT @cnt = (SELECT 1 FROM dbo.t1 (index ix01)
WHERE f1 = @p1
)
SET ROWCOUNT 0
Appreciate your help.
How To Get Index Seek
May 7, 2008Hi,
Can I use index seek and still keep 'like' 'or' functionality for the following statement?
--prepare test table
create table entity (Id int identity(1,1), FamName varchar(200), LastName varchar(200))
go
create clustered index entity_id on entity (id)
go
create nonclustered index entity_lastName on entity (lastName)
go
insert into entity select famName,FirstName from table
--test index
declare @LastName varchar(10)
set @LastName = 'a'
select FamName
from entity
where @LastName is null or LastName like @LastName --clustered index scan
How To Get Rid Of Table Scan
May 26, 2000Can anyone tell me how to get rid of the Table Scan(1 million rows)being performed on the
The last line, option (loop loin) stopped table scanning the B.ss_manifest and started using the index, I'd like both tables to use the index.
This is the argument I get from execution plan under the table scan.
Object ((D4000).(dbo).(shipstop)as (A))
update drivers set dr_miles_run = case when D1.miles > 0 then d1.miles else 0 end
from (select mf_dr_nbr, sum( case when A.ss_end_dt < '05/17/00' then
( cast((datediff(day, '05/17/00' , B.ss_end_dt ) + 1) as float) /
cast( (datediff(day, A.ss_end_dt , B.ss_end_dt ) + 1) as float) * mf_ld_miles)
else mf_ld_miles end) as miles
from manifest, shipstop A, shipstop B
where mf_manifest_nbr = A.ss_manifest_nbr
and mf_manifest_nbr = B.ss_manifest_nbr
and A.ss_stop_type in ('OR','SA')
and B.ss_stop_type in ('DT','RD')
and ((A.ss_end_dt >= '05/17/00 00:00' and A.ss_end_dt < '05/24/00 00:00')
OR ((B.ss_end_dt >= '05/17/00 00:00' and B.ss_end_dt < '05/24/00 00:00'))) and mf_status > 3 group by mf_dr_nbr ) as D1
where Drivers.dr_driver_nbr = D1.mf_dr_nbr
option (loop join)
Thanks for any ideas!
Table Scan
Jul 9, 2007Does SQL Server allow a table scan to be used when querying a table that has a clustered-index? If yes, could someone please show me the syntax? I have tried with (index(0)) but this appararently means a clustered index scan when there is a clustered index on the table to be queried.
Or does clustered index scan mean the same thing as a table scan when the table has a clustered index? Confused.
Thanks
Table Scan
Nov 28, 2007Friends,
I am using this query in a table with 29,000 records having non-clustered index on emp_id
select * from employee
where emp_id between 100 and 1000
and gender = 'M'
order by emp_id
execution plan shows a table scan in table employee. Any reason?
select * from employee with (index = emp_id)
where emp_id between 100 and 1000
order by emp_id
ofcourse this uses index seek
regards,
Priw
Is My Table Scan Unavoidable?
Jun 10, 2004Hi guys-n-gals...
I have a table that contains the following:
PortfolioID(int), EndDate(smalldatetime), Begdate(smalldatetime), WklyCloseIndex (float)
It has a primary key which is PortfolioID/BegDate/EndDate
I need to create a table that summarizes, by date range, the weeklycloseindex of several portfolios, like this:
BegDate EndDate Portfolio2 Portfolio67 Portfolio11 Portfolio90
05/28/2004 06/04/2004 xx.xx xx.xx xx.xx xx.xx
05/21/2004 05/28/2004 xx.xx xx.xx xx.xx xx.xx
So I wrote a function...
This function results in a table scan *GASP!!!!* (at least that's what the 'splain plan tells me when I run it in SQL Analyzer). Before I made it into the function, when I was testing the code in SQL Analyzer, it resulted NOT in a table scan, but rather a series of nested loops (the joins) and clustered index seeks...resulting in about 1/3 the total cost of the function.
I suspected originally that it was the TOP/ORDER BY that the function insisted upon, but even if I remove those, still get a table scan.
Wassup? Why does the function turn my cool lil' self-join into a table scan? Whut am I missing? Any thoughts? Disgusted Derisions? Hurled Insults? Bring it on!!! (please! ;) )
My predecessor did this in a similar project using a separate cursor for each portfolio by date, then looped through the dates, pulling in the per-portfolio index value and building the output table. I would rather avoid the cursors if I can.
Table-Scan Speed
Oct 2, 2007I have the following scenario (with 2K5 Express)
I have a table with 160.000 records.
I have to retrieve 10.000 - 40.000 records by their ids (<3seconds would be sufficent)
I first used single requests, then one single command as batch (simply joined the single commands into one string).
But that was very slow (30 seconds if cached). so I created one big statement
select myfields
from mytable where id in(1,2,..,35000)
if everything is cached the speed is fine (<1second), but if I retrieve the data for the first time
it takes 15-30 seconds, that's a bit too slowish.
the total database size is 100MB - so a file scan should be faster, I thought at least
so HERE is the problem why I post this
to force the table scan I used
Select myFields From mytable With (Index(0) ...
that took > 3 minutes
I tested the raw IO-time, that was 2,5-3 seconds with the db-file
has SQL Server a problem with the 35.000 items in the condition?
(If it loopes 35.000 x 160.000 times instead of using a hash for the items that would explain the slow speed)
or another reason:
is table scanning always much slower then the raw io operations?
the id-index is not grouped and ( I really don't know why) not marked as primary key,
but that shouldn't have any impact on a file-scan, I guess.
Has anyone faced (and solved) a similiar problem?
Optimize Query - How To Make It An Index Seek
Jun 21, 2004create table t1(a varchar(50) , b varchar(50))
create index i1 on t1(a)
create index i2 on t1(b)
create view v1
as
select * from t1 where isnull(a,b) = 'test'
select * from v1
The above SQL "select * from v1" is doing a table scan.
What do I do to make it perform an index seek ????
TIA
- ForXLDB
Table Scan On Inserted And Deleted Tables?
Apr 30, 2001Hello,
I have a stored procedure that's running a little slower than I would like. I've executed the stored proc in QA and looked at the execution plan and it looks like the problem is in a trigger on one of the updated tables. The update on this table is affecting one row (I've specified the entire unique primary key, so I know this to be the case). Within my trigger there is some code to save an audit trail of the data. One of these statements does an update of the history table based on the inserted and deleted tables. For some reason this is taking 11.89% of the batch cost (MUCH more than any other statement) and within this statement 50% of the cost is for a table scan on inserted and 50% is for a table scan on deleted. These pseudo-tables should only contain one record each though.
Any ideas why this would be causing such a problem? I've included a simplified version of the update below. The "or" statements actually continue for all columns in the table. The same trigger template is used for all tables in the database and none of the others seem to exhibit this behavior as far as I can tell.
Thanks for any help!
-Tom.
UPDATE H_MyTable
SET HIST_END_DT = @tran_date
FROM H_MyTable his
INNER JOIN deleted del ON (his.PrimaryKey1 = del.PrimaryKey1) and
(his.PrimaryKey2 = del.PrimaryKey2)
INNER JOIN inserted ins ON (his.PrimaryKey1 = ins.PrimaryKey1) and
(his.PrimaryKey2 = ins.PrimaryKey2)
WHERE (his.HIST_END_DT is null)
and ((IsNull(del.PrimaryKey1, -918273645) <>
IsNull(ins.PrimaryKey1, -918273645)) or
(IsNull(del.PrimaryKey2, -918273645) <>
IsNull(ins.PrimaryKey2, -918273645)) or
(IsNull(del.Column3, -918273645) <>
IsNull(ins.Column3, -918273645)))
SQL 2012 :: Table Scan In Query Tuning
Mar 21, 2014I am doing sp tuning. It has several lines. SO I divided into several small queries and executed individually and check the execution plans. In one small query, I found table scan is happening. That query is basically retrieving all columns from a table but the table doesn't have any pk or Indexes. So is it better to create non-clustered index to remove table sca.
View 2 Replies View RelatedNorthwind - Execution Plan Bug? Why Index Seek And No Bookmark Lookup?
Dec 10, 2006If you display the execution plan and run the following:SET STATISTICS IO ONgoSELECT ProductID, SupplierIDFROM ProductsWHERE SupplierID = 1I don't understand how come there is noBookmark Lookup operation happening to get theProductID?I only see an Index Seek happening on SupplierID.There is no composite index SupplierID + ProductIDso what am I not understanding here?Thank you
View 3 Replies View RelatedAvoid Table Scan Using Multi Union View
May 26, 2008Anyone see a way to trick the optimizer into not scanning all tables involved in the view?
-- create two test tables
create table dbo.test1
(testID int, TestName varchar(10))
create table dbo.test2
(testID int, TestName varchar(10))
-- populate
declare @i int
set @i = 1000
while @i > 0
begin
insert into dbo.test1
select @i, '1.' + cast(@i as varchar(5))
set @i = @i - 1
end
insert into dbo.test2
select 1, '2.1' union all
select 2, '2.2'
go
-- create view
create view dbo.vw_Test
as
select1 as QueryID,
TestName
fromdbo.Test1
union all
select2 as QueryID,
TestName
fromdbo.Test2;
go
-- this works as i want, only scans table dbo.Test2
select *
fromdbo.vw_Test
whereQueryId = 2
-- joining to a table triggers scan of both tables in view:
declare @table table (QueryID int)
insert into @table
select 2;
selectvt.TestName
fromdbo.vw_Test vt
join@table t on
vt.QueryID = t.QueryID
Using the showplan I can see why the optimizer ends up scanning all tables, but maybe there is a way to force it to use the QueryID param evaluation earlier in the filtering.
Nathan Skerl
Create TRIGGER Remove White Spaces From A Fields In Table-scan And Fix
Apr 21, 2008hi
i have table i use it for update insert
and the users use this table from a grid on the web
and i need to prevent from white space in the fields in table
so how to
create TRIGGER remove white space from a fields in table scan and fix it ?
Code Snippet
SELECT TRIM(fieldname)
, LTRIM(fieldname)
, RTRIM(fieldname)
, LTRIM(RTRIM(fieldname))
FROM tablename
Code Snippet
WHERE (LTRIM(RTRIM(fieldname)) = 'Approve')
Code Snippet
replace(@text,' ','')
create TRIGGER on update insert and not to damage the text in the all fields
TNX
The Index Entry For Row ID Was Not Found In Index ID 3, Of Table 357576312
Jul 9, 2004Hi,
I'm running a merge replication on a sql2k machine to 6 sql2k subscribers.
Since a few day's only one of the merge agents fail's with the following error:
The merge process could not retrieve generation information at the 'Subscriber'.
The index entry for row ID was not found in index ID 3, of table 357576312, in database 'PBB006'.
All DBCC CHECKDB command's return 0 errors :confused:
I'm not sure if the table that's referred to in the message is on the distribution side or the subscribers side? A select * from sysobjects where id=357576312 gives different results on both sides . .
Any ideas as to what is causing this error?
Advantages Of Using Nonclustered Index After Using Clustered Index On One Table
Jul 3, 2006Hi everyone,
When we create a clustered index firstly, and then is it advantageous to create another index which is nonclustered ??
In my opinion, yes it is. Because, since we use clustered index first, our rows are sorted and so while using nonclustered index on this data file, finding adress of the record on this sorted data is really easier than finding adress of the record on unsorted data, is not it ??
Thanks
Scan
Oct 8, 2007
I write a work about database, and I want to write the diffrence between Table scan and Index scan. When is the index scan effectient? Use the database a Table scan when there is an index on the table or always a index scan when the index is nonselective? Can be a Table Scan effecient than a index scan?
Scan Density < 50%
Aug 14, 2001I am having problems w/ the indexes on a particular table. Currently the scan density if 25%. I have ran the dbcc dbreindex and the scan density does not improve. I have manually dropped and recreated all of the indexes on the table (there are only two) and still no help.
I have a clustered Primary Key index on my part_number and project_number fields and another index on the project_number field. If I drop the second index and only have my primary key index, it still doesn't help. The fill factor was originally set to 90% and I changed this to 30%, 20%, 10%, 0% and the best scan density I could acheive was 50%.
The data in this table is not updated that often, on average about 15 records a day are updated, and there are only 107 records. This is a small table, but there is a possibility for it to grow rapidly and I want to be prepared now.
Does anyone have any ideas or suggestions? I've tried everything I can think of with no luck.
TIA,
Chris
Count Scan
Aug 21, 2006Hi,
I have a simple temp table which looks like this:
CREATE TABLE #t7e07c01fa80143ff84cb14a2307809f7
(
[AUTOID_TEMP] [int] IDENTITY (1, 1) NOT NULL,
...
)
ON [PRIMARY]
ALTER TABLE #t7e07c01fa80143ff84cb14a2307809f7 ADD
CONSTRAINT [PK_t7e07c01fa80143ff84cb14a2307809f7] PRIMARY KEY NONCLUSTERED
(
[AUTOID_TEMP]
)
ON [PRIMARY]
Insert Into #t7e07c01fa80143ff84cb14a2307809f7
Selet columns... from t....
-- get total records
Declare @TotalCount as int
select @TotalCount = count(AUTOID_TEMP) from #t7e07c01fa80143ff84cb14a2307809f7
Now the above last statement does a index scan. I am new to indexing/tuning and was wondering if its normal - if so why and can I somehow enhance this?
Thanks
Scan Directory
Nov 1, 2007Hey guys,
I have a procedure that runs everyday which takes the IIS log file from the previous day and imports it and calcs values. I would like to change this from taking the previous day to scanning all the file names in the folder and comparing them to a database to see if they have already been scanned before. I already have a table called DatesScanned which lists the filename and scandate.
IE:
D:Logsfile1.log
D:Logsfile2.log
D:Logsfile3.log
D:Logsfile4.log
The 4 file names will be scanned and compared to DatesScanned to see which has been imported already.
Can anyone point me to a resource or information on how I would get the directory listing of a folder so I could compare it to the DatesScanned table.
Thanks a bunch!
Jeff
Scan Count
Jul 23, 2005Hi,Can someone please explain the following1. Meaning of scan count as reported when "statistics io" is turned onprior to running a query.2. In which situations could you have an identical database runningon two diferent servers , with identical database serverconfigurations, running identical queries, with identical query plan,report large discrepency in the scan count . This is one of thepossibilities we are looking at in terms of the reason why one serverruns the job in 12 hours and the other in 24 hours.Server 1--------Table 'TRANS_HISTORY'. Scan count 216, logical reads 897093, physicalreads 44, read-ahead reads 900599.SQL Server Execution Times:CPU time = 27766 ms, elapsed time = 46850 ms.UNIT_NUMBERACCOUNT_TYPETRANSACTION_TYPEServer 2--------Table 'TRANS_HISTORY'. Scan count 491, logical reads 952759, physicalreads 51, read-ahead reads 954414.SQL Server Execution Times:CPU time = 31563 ms, elapsed time = 145595 ms.UNIT_NUMBERACCOUNT_TYPETRANSACTION_TYPEI thank you in advance for your assistance.Puvendran
View 1 Replies View Related