IF NOT EXISTS (... - EXISTS TABLE : Nested Iteration. Table Scan.Forward Scan.
Sep 20, 2006
Hi,
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.
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Jan 29, 2006
How 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?
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Oct 4, 2007
Hey,
what is the difference between Table Scan und Index Scan?
I find no difitions in the internet
Finchen
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Sep 21, 2007
Hi,
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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Jun 6, 2007
Hi.Like in subject. I know the varray and nested tables from oracle, and I'm trying to implement them in sql server. I've been googling for any information but with no result. Can somebody direct me ??Sorry for any english mistakesThanks for help
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May 26, 2000
Can 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!
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Jul 9, 2007
Does 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
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Nov 28, 2007
Friends,
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
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Jan 16, 2002
Hi 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
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Jun 10, 2004
Hi 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.
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Oct 2, 2007
I 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?
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Sep 29, 2006
I 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
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Apr 30, 2001
Hello,
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)))
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Mar 21, 2014
I 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.
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Mar 28, 2014
I 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 '
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May 26, 2008
Anyone 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
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Sep 19, 2015
I'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.
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Apr 21, 2008
hi
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
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Jun 21, 2015
Previously same records exists in table having primary key and table having foreign key . we have faced 7 records were lost from primary key table but same record exists in foreign key table.
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Jul 14, 2015
I need to find out if a Transaction ID exists in Table A that does not exist in Table B. If that is the case, then I need to insert into Table B all of the Transaction IDs and Descriptions that are not already in. Seems to me this would involve If Not Exists and then an insert into Table B. This would work easily if there were only one row. What is the best way to handle it if there are a bunch of rows? Should there be some type of looping?
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Nov 15, 2001
I am trying to write a query that does not use inner joins to see if it returns rows faster than a query using inner joins.
My trouble is that I don't know how to write the syntax for the 3rd table that I am comparing against.
Can I nest Exists in a Where clause?
If so how is the 2nd exists statement added to the query?
see my sample query below
================================================== ===
'With 2 tables
SELECT DISTINCT s1.ID, s1.SITE
FROM SITE_TBL s1
WHERE EXISTS (SELECT *
FROM DEVICE_TBL d1
WHERE s1.ID = d1.SITE_ID AND d1.DELETEFLAG <> 'D')
ORDER BY SITE
'with 3 tables this doesn't work
SELECT DISTINCT s1.ID, s1.SITE
FROM SITE_TBL s1
WHERE EXISTS (SELECT *
FROM DEVICE_TBL d1
WHERE s1.ID = d1.SITE_ID AND d1.DELETEFLAG <> 'D')
AND
(SELECT *
FROM BIG_TBL b1
WHERE d1.fqdn = b1.xyz)
ORDER BY SITE
================================================== ===
Thanks for the help
Jim
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May 7, 2007
I have a textbox1 control where a zip code is entered. What is the most efficient way in C# code behind to see if that zip code exists in tblZipCode? I only need to know if it is there, do not need to know how many occurances.
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Jun 10, 2008
HI,
having a problem with a data loading from 2005 to 2000. Im using export & import wizard. But the problem comes when the user drops a table on 2005. Anyway to check if table exista then use the E&I to load the data.
I cant use the BCP as xp_shellcmd is disable.
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Jan 17, 2008
Hi all,I am in the process of creating a page that checks to see if a particular user exists in the database and if it does then send to welcome.aspx if not then accessdenied.aspx. The userid is requested from the query string.I have done some research and cannot find anything directly related, I have tried to add bits of code into what i think is the right place but I dont think what i am doing is correct. Can someone help and show me where my code is going wrong? Also is there a better/more efficient way to do what I am doing?Thanks in advance. default.aspx.csusing System;using System.Data;using System.Data.SqlClient;using System.Configuration;using System.Web;using System.Web.Security;using System.Web.UI;using System.Web.UI.WebControls;using System.Web.UI.WebControls.WebParts;using System.Web.UI.HtmlControls;public partial class _Default : System.Web.UI.Page{ protected void Page_Load(object sender, EventArgs e) { string UserID = Request.QueryString["uid"]; //string TransferPage; if (UserID != null) { //initiate connection to db SqlConnection objConnect = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["MyConnection"].ConnectionString); string sql = "SELECT COUNT(*) FROM members WHERE UserID = '" + UserID + "'"; SqlCommand query = new SqlCommand(cmd, test); int count = (int)query.ExecuteScalar(); int aantal = -1; // some default value if can't insert record if (count == 0) // no existing record for username { Server.Transfer("accessdenied.aspx"); } else { Session["UID"] = UserID; Server.Transfer("welcome.aspx"); } } }}
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Feb 9, 2008
i am using vb.net and ms sql server 2005 express.....what is the syntax for dropping a table if existsi have used this but it says incorrect syntax near if Dim cmda As New SqlCommand("drop table " + test + " if exists", New SqlConnection(strdb)) cmda.Connection.Open() cmda.ExecuteNonQuery() cmda.Connection.Close()any solutions???? plz only answer in vb.net and sql server express
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Sep 14, 2000
What is the best way to programmatically determine if a temp table exists? In 6.5, I would use
IF EXISTS(SELECT * from tempdb..sysobjects where id = object_id('tempdb..#MyTable') and type = 'U')
But now that it is strongly discouraged to code against system tables, how could I re-write this statement?
The proper way to check the existence of a table would be:
IF OBJECTPROPERTY(object_id('tablename'), 'IsTable') = 1
However, to get this to run for a temp table, I think you'd have to change the database context to tempdb and then back to your database. That doesn't seem efficient.
I could use
IF object_id('tempdb..#MyTable') IS NOT NULL
But that's not guarenteeing that it's a table, right?
Any ideas?
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May 2, 2000
How do I find out if a temporary table named '##test' exists? I have a stored
procedure that creates this table and if it exists another stored procedure
should do one thing, if it does not exist I want the SP to do something else.
Any help as to how I can determine if this table exists at the current time
would be greatly appreciated.
Thanks in advance for you help,
Jon
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Aug 10, 1999
I need a snippet of code that will determine wether or not a table exists in a database...
thanx
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Feb 18, 2004
in mysql i can drop a table or db if it currently exists using
drop table if exists [table1] or
drop database if exists [db1]
is there an equalivant in ms sql
thanks
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May 20, 2008
Hi,
This my first time using the link server to read the files directly from within SQL2005, so issues the following link:-
EXEC sp_addlinkedserver
@server = N'MYVFPSERVER', -- Your linked server name here
@srvproduct=N'Visual FoxPro 9', -- can be anything
@provider=N'VFPOLEDB',
@datasrc=N'"C:PROGRAM FILESMICROSOFT VISUAL FOXPRO 9Samplesdata estdata.dbc"'
After that i can open query and do the import issues, but how can check if the table exists before issues the query.
Best regards
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Jan 26, 2006
Hi,I am trying to create a script that deletes transaction tables and leavesmaster data like customer, vendors, inventory items, etc. How can I useTRUNCATE TABLE with an Exists? My problem is I have 200+ tables, if Isimply use a list like:truncate table01truncate table02truncate table03....I get errors if the table does not exist and have to manually run thetruncate statements. Some tables may not exist if that part of the app isnever used. I'm trying to make a list of all tables that could existwithout it erroring out 50+ times.Thanks in advance.
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Sep 14, 2006
What’s the easiest way to check if a single value exists in a table column? I’m building a simple login page, and I want to get the username and check if it exists in my Users table. Here’s my SQL: SELECT UserID FROM UsersWHERE UserID = "admin" Could someone give me code to check for “admin” in my UserID column? Here’s some code I tried, using my SqlDataSource, but it returns an error “Could not load type 'System.Data.OleDb'” protected void Button1_Click(object sender, EventArgs e) { // Retreive the results from the SqlDataSource as a DataReader OleDbDataReader reader = (OleDbDataReader) SqlDataSource1.Select(DataSourceSelectArguments.Empty); // Read in the value if (reader.Read()) { } // Close the reader reader.Close(); } I don’t have to use the SqlDataSource, but originally thought it might be easier. I know how to use SqlDataSource to fill a whole GridView but this is different.
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Jun 17, 2008
Basically, i am still relatively new to ASP.net and SQL. And i have the following query.
I have a skills table to which the user enters their skills using the following fields: Skillcatagory, SKill, Current Level, Target Level, target date and comments and the serial of the user.
I need to check via our staff table, which people have had a skill entered for them. And then produce a report on who has not had a skill entered for them.
This table has a serial of the user column aswell which is unique.
If there is more information that i can give you to assist me, please ask me.
You help would be greatly appreciated.
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