Index Help To Avoid Table Scan
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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Jul 23, 2005
Hi,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%'
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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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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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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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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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Oct 20, 2006
please 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
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Mar 1, 2004
I 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
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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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Nov 14, 2006
the 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?
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Nov 4, 2002
I 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
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Apr 8, 2008
I 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?
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Oct 26, 2006
Greetings,
I have two tables:
CustomerOrder
----
ID
CustomerID
StatusID
CustomerOrderDetail
----
ID
Order_ID
StockID
Quantity
CustomerOrderDetail table has clustered unique index for ID and non-clustered for Order_ID
SQL Server 2005 is using table scan for CustomerOrderDetail table When I user the following query:
select
cod.*
from CustomerOrder co
inner join CustomerOrderDetail cod ON cod.Order_ID = co.ID
where
co.StatusID = 8 -- Pending
Both of the tables are pretty big, detail table has more than million records, so scanning the table is a bad idea.
When I specify hint to use index then sql seeks, but how do I make SQL server to use index automatically? I don't want to use hints in my queries.
Thanks!
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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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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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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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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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Nov 19, 2015
There are 3 tables Property , PropertyExternalReference , PropertyAssesmentValuation which are common for 60 business rule
SELECT Â
 PE.PropertyExternalReferenceValue  [BAReferenceNumber]
, PA.DescriptionCode
  [PSDCode]
, PV.ValuationEffectiveDate
  [EffectiveDate]
, PV.PropertyListAlterationDate
  [ListAlterationDate]
[code]....
Can we push the data for the above query in a physical table and create index to make the query fast rather than using the same set  tables multiple timesÂ
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Nov 2, 2015
INSERT
INTO [Table2Distinct]Â Â Â Â Â Â Â Â
([CLAIM_NUMBER]Â Â Â Â Â Â Â Â
,[ACCIDENT_DATE]
[code]....
I used the above query and it still inserts all the duplicate records. What is wrong with my statement?
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Jul 9, 2004
Hi,
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?
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Jul 3, 2006
Hi 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
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Jul 23, 2005
To any and all;I have a very large table (16Mil+ records), for which I want to deleteabout 8 Million records. There are a few indexes on this table.Is there a way that I can run either a query or a series of queriesthat will run against each record and delete based on criteria (date)?If I do a single DELETE query, it will take forever, lock the table,and my app that runs against it will stop INSERTING, which is bad.If I do a cursor, I think it locks the table also, so that won't do,right?Any help would be appreciated.Glenn DekhayserContentcatcher.com
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Jan 21, 2015
I am trying to think of a way to read a control table, build the SQL statement for each line, and then execute them all, without using a cursor.
To make it simple... control table would look like this:
CREATE TABLE [dbo].[Control_Table](
[Server_Name] [varchar](50) NOT NULL,
[Database_Name] [varchar](255) NOT NULL,
CONSTRAINT [PK_Control_Table] PRIMARY KEY CLUSTERED
[Code] ....
So if we then load:
insert into zt_Planning_Models_Plant_Include_Control_Table
values ('r2d2','planing1'), ('r2d2','planing7'), ('deathstar','planing3')
Then you would build a SQL script that would end up looking like the following (note all the columns are the same):
insert into master_models
Select * from r2d2.planning1.dbo.models
insert into master_models
select * from r2d2.planning7.dbo.models
insert into master_models
Select * from deathstar.planning3.dbo.models
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Jul 13, 2007
I want to grant access on the below view for an end user so that he connect to our SQL server and retrieve data. The view looks like the below
CREATE VIEW DB1.[dbo].[View1]
AS
-- For brevity, I made it as simple statement.
SELECT *
From DB2.dbo.table2
GO
For the above view, it looks like I have to grant select and connect permission for the DB1. [dbo].[View1] as well as DB2.dbo.table2.
1. Is my understanding correct?
2. I want the user to access only DB1. [dbo].[View1] and not the underlying tables. Is there a way to grant access only on the view and execute the statement on a different security context so that the user can€™t access DB2.dbo.table2 directly?
3. When the user uses SQL Server Management Studio to connect to SQL server, he is able to connect and select DB2.dbo.table2 directly. Is there any way to restrict user from viewing and executing select statement on DB2 database from SQL Server Management Studio
Thanks in advance for your help
With regards
Ganesh
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Jun 10, 2014
I created a Fact Table with 3 Keys from dimension tables, like Customer Key, property key and territory key. Since I can ONLY have one Identity key on a table, what do I need to do to avoid populating NULLs on these columns..
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Oct 22, 2015
I have a job which executes hourly.
Essentially:
Begin
Truncate table A
Insert into A
(Col1,
Col2,
Col3...
)
Select Value1,
Value2,
Value3...
From Table B
End
The insert operation query takes approximately 3.5 minutes to execute. What's occurring is the Table is immediately truncated, and there are no rows in the table for those 3.5 minutes.
How can I avoid having this gap - where there are no rows in the table for that period of time during the job execution ? The table could be locked, but that doesn't seem like the best solution.
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