Index Design Recommendation - Examine Column Uniqueness
Nov 30, 2005
I am reading "SQL Server Query Performance Tuning Distilled",
on page 104 it talks about one of the index design recommendations
which is to choose the column that has very high selectivity of values
instead of a column that has very few selectivity of values.
My question is if I have currently indexes on my tables that have
1, 2, 3, 4, ... values only on thousands of rows, are these nonclustered
indexes pretty much useless indexes that I should get rid of?
And I know that pretty much the number of selectivity values will
always remain very low.
Thank you
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Sep 4, 2004
I want to make sure that usernames and folder names (that are stored in the database) are all unique when created by the admin through an admin control panel.
How would I code and use an Index to make sure that the 2 columns are unique?
I've looked at examples on the net but nothing is telling me how I can create an index through Enterprise Manager? Thanks
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Sep 4, 2004
I want to make sure that usernames and folder names (that are stored in the database) are all unique when created by the admin through an admin control panel.
How would I code and use an Index to make sure that the 2 columns are unique?
I've looked at examples on the net but nothing is telling me how I can create an index through Enterprise Manager? Thanks :)
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Jan 23, 2008
Is there a system table column to query to determine whether an index is defined as unique in SQL Server 2000? It is easy to find this info in SQL Server 2005, but I don't see a valid column for this on dbo.sysindexes.
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Sep 25, 2007
Hi,
What's the most efficient way to store the following information:
* Table contains 1 million listings
* Each listing can be geo-targeted to any of the 200+ countries
* Searches return listings based on location
Storage options:
Option #1 (normalized)
* Listings (PK listingID int) [1 million rows]
* ListingLocations (listingID, locationID) [could be up to 200 million rows]
Option #2 (denormalized)
* Listings (PK listingID int, binary(32) with bit-mask consisting of 200 bits one for each location)
Usage: Usually the query will simply lookup listings based on some keywords. It will get back 50-200 listings. Then the application (C#) will filter the listings based on location.
Did anyone have experience with similar structures? Which option is more efficient?
I know that using the intersection-table in Option #1 is the "proper" relational-DB way of doing things. However, I do not like the idea of storing the listingID so many times (ones for each locationID).
Thanks,
Av
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Oct 20, 2015
can you have constraints as such [CreateBy] [nvarchar](30) NOT NULL DEFAULT (suser_sname()),on a table that has a column store index in SQL Server 2012,2014, or 2016?
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Apr 2, 2007
I would like to have some clarification about index-related recommendation from Database Tuning Advisor.
Let me describe the scenario first:
There is a table with clustered index defined on ID column of type INT and there are other columns of varchar/int types as well. Now when I run tuning advisor I get recommendations related to creating statistics as well as non-clustered indexes. When I view the syntax for recommended non-clustered index, sometime it explicitly add ID column as well which already has clustered index defined on it. e.g
CREATE NONCLUSTERED INDEX idx_TableName_IndexName ON dbo.TableName
(
ColName1 ASC,
ColName2 ASC,
ID ASC
)
My understanding is that for each non-clustered index, clustered index is automatically a part of it and that is how non-clustered index retrieve the actual data. I have seen it more often than not in DTA's recommendation to include clustered index column somewhere among columns for indexing for so many of my tables.
I can understand if the recommendation was to INCLUDE clustered-index column.
I would appreciate if someone out there could help me to understand what I am missing here.
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Oct 5, 2015
We have a vendor created database with 9000+ tables, one of which has about 6 billion rows. The vendor redesigned the database recently and ever since we've had terrible performance.
What the vendor did was increase any and all varchar columns (tens of thousands of columns) to 256.
Before the upgrade we had no problems creating an index on the 6billion row table, it would take 2 hours.
Now after the upgrade we've let the index creation command run for 5 days and killed it because it was consuming terabytes of logspace.
The previous design had combined column width of 1049 to what is now over 4000. The primary key itself is 1283 characters (SQL limit is 900).
There is no additional data, just wider columns. Why we are unable to create the index?
What is happening inside SQL Server? Does SQL make "room" in memory for the index for the entire width of the potential max row length?
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Nov 24, 2015
I created composite clustered index key based on Gender and Salary column
The Query executed Successfully and <g class="gr_ gr_135 gr-alert gr_tiny gr_spell undefined ContextualSpelling multiReplace" data-gr-id="135" id="135">i</g>
got composite index key id Gender(-), Salary I <g class="gr_ gr_310 gr-alert gr_gramm undefined Grammar only-ins replaceWithoutSep" data-gr-id="310" id="310">want</g> know why Gender(-) display like this?
And Gender is <g class="gr_ gr_391 gr-alert gr_spell undefined ContextualSpelling ins-del multiReplace" data-gr-id="391" id="391">nvarchar</g> (20)
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Dec 5, 2007
Dear All.
We had Teradata 4700 SMP. We have moved data from TD to MS_SQL SERVER 2003. records are 19.65 Millions.
table is >> Order_Dtl
Columns are:-
Client_ID varchar 10
Order_ID varchar 50
Order_Sub_ID decimal
.....
...
..
.
Pk is (ClientID+OrderId+OrderSubID)
Web Base application or PDA devices use to initiate the order from all over the country. The issue is this table is not Partioned but good HP with 30 GB RAM is installed. this is main table that receive 18,0000 hits or more. All brokers and users are using this table to see the status of their order.
The always search by OrderID, or ClientID or order_SubNo, or enter any two like (Client_ID+Order_Sub_ID) or any combination.
Query takes to much time when ever server receive more querys. some orther indexes are also created on the same table like (OrderDate, OrdCreate Date and Status)
My Question are:-
Q1. IF Person "A" query to DB on Client_ID, then what Index will use ? (If any one do Query on any two combination like Client_ID+Order_ID, So what index will be uesd.? How does MS-SQL SERVER deal with these kind of issues.?
Q2. If i create 3 more indexes on ClientID, ORderID and OrdersubID. will this improve the performance of query.if person "A" search record on orderNo so what index will be used. (Mind it their would be 3 seprate indexes for Each PK columns) and composite-Clustered index is also available.?
Q3. I want to check what indexes has been used? on what search?
Q4. How can i check what table was populated when, or last date of update (DML)?
My Limitation is i Dont Create a Partioned table. I dont have permission to do it.
In Teradata we had more than 4 tb record of CRM data with no issue. i am not new baby in db line but not expert in sql server 2003.
I am thank u to all who read or reply.
Arshad
Manager Database
Esoulconsultancy.com
(Teradata Master)
10g OCP
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Aug 24, 2007
I have written a few custom tasks and I've noticed that they don't behave exactly like the built-in MS tasks when in design mode. Specifically, they don't update themselves with the values of expressions that have been assigned to their custom properties.
Here's an example. My task exposes a property called JobNumber. Let's say I make a variable called @[User::JobNumber], give it a value, and assign the variable as an expression to the JobNumber property. When I look at the properties in either the property window or my custom UI editor, the value assigned to the variable never shows up in the property itself. If, on the other hand, I were to assign a variable to the ServerName property of an OLEDB connection manager, the next time that task validates itself I will see the value of my variable in the ServerName property.
Everything works fine at run-time; it's just design-time that the behavior is undesirable.
I'm sure this is because I need to be doing something myself, but the question is what, and when?
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Oct 22, 2007
Hi all,I have a very large table with many columns: dateTime type, nvarchartype and integer field type.A program exec many type of query with where clause.Data field is always in where clause, but some other field is presenttoo. Sometimes integer field, sometimes nvarchar field.Now I must create index for the query!For choose index field what i can do?I must create only index on a datetime field or every combination inevery type of query?In the second case I must create very much index! But this is verydispendious for update/insert/delete operation on the table!!!Some ideas?thnx
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Apr 4, 2007
I want to create an index that will cause the cost of the query to be as low as possible and also
must minimize the space that is used by the index. What type of index/parameters I can associate when I create an Index. I already have a clustered index
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Apr 25, 2008
When should a composite index be created in favor of multiple single colum indexes?
thanks
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Jul 6, 2015
I want to have table with 1 PK and 1 Clustered Index on Column2 and Id, this is my code:
CREATE TABLE [dbo].[Test] (
[Id] INT PRIMARY KEY NOT NULL IDENTITY(1,1),
[Column2] INT NOT NULL,
[Column3] INT NOT NULL,
[Column4] INT NOT NULL,
);
CREATE CLUSTERED INDEX IX_Test ON dbo.Test (Column2, Id);
Error: "Cannot create more than one clustered index on table..."I know, that PRIMARY KEY automatically create Clustered index on Id.Then I manually delete existing Clustered index, and run this code part again:CREATE CLUSTERED INDEX IX_Test ON dbo.Test (Column2, Id);Everything is fine, except I lost my PK on Id...How can I leave PK on Id and create my custom Clustering Index?
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Apr 13, 2008
I'm having some difficulties getting sql server replication to properly filter joined tables to my subscribers. I would like to examine the contents of the view the system uses to select the data from my subsidary tables. Unfortunately these views are marked as system views, and I cannot view the underlying SQL clause.
I imagine this data is stored somewhere in yet another system table... does anyone know how I can examine the sql statement of a view that is marked as a 'system view'?
Thanks,
MD
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Aug 27, 2015
I have table which having clustered index based on column (A,B,C,D,E,F).Now my query based on B,D,F. e.g: where b='Test1' and D='test2' and F='test3' Now Execution plan ask to create non clustered index with (B,D,F) column.is it make any sense to create non clustered index where clustered already available.
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May 25, 2015
I have a table called as A table :
CREATE TABLE [dbo].[A](
[AutoID] [int] IDENTITY(1,1) NOT NULL,
[ProID] [int] NOT NULL,
[LID] [varchar](12) NOT NULL,
[EventID] [varchar](12) NOT NULL,
[HEventID] [varchar](12) NULL,
) ON [PRIMARY]
How I should creating the appropiate index for this table?A few option that I think ok.
Opt 1 : creating a primary key on the autoID with create index . create non clustered index on ProID and EventID
Opt 2 : create a primary key on the autoID with non clustered index . create clustred index on ProID and EventID .
opt 3: create primary key on the ProID and EventID with clustered index.
I have read thru the article on the primary key, clustered and non clustered indexing. However when I want to applyied the indexing..I feel a bit lost.But among the 3 option.... what is the different..
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May 7, 2008
I am trying to selectively show or hide a table based on the values in a multi valued parameter. How can I examine all values (simulate the like functionality) within an expression?
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Oct 7, 2015
Here is the DDL of a table that I am trying to add an identity column and create a clustered index. I am using SQL 2012 SE
CREATE TABLE [dbo].[IPF](
[IPFId] [uniqueidentifier] NOT NULL,
[IPId] [uniqueidentifier] NOT NULL,
[FId] [uniqueidentifier] NULL,
[FName] [nvarchar](50) NULL,
[FItemId] [uniqueidentifier] NULL,
[code]....
The table currently has 220million rows. I am trying to add a new identity new column and create a clustered index on it. I ran the script and its been more than 26hrs and its still running. I ensured there is no blocking.
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Aug 25, 2014
Someone claimed that the query:
INSERT INTO [table1] SELECT * FROM [table1]
was a result of running DBCC DBREINDEX.I wasn't able to replicate this when I did a trace on my local machine, but SQL Monitor from Red-Gate shows that query happening for at least some of the tables that are being reindexed via a job. Is there anyway to examine the actual code inside DBREINDEX to see exactly what commands it may execute?
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Oct 5, 2015
How Can I Create Two Column with Math Function In one Column Like Below.
Create Table Tbl_V_Voucher_Details
(
Id Int IDentity (1,1) Primary Key,
Catid Int Foreign Key References Tbl_V_Voucher_Info(Id),
ItemId Int Foreign Key References Tbl_V_Item(Id),
Discription varchar
(100),
Qty Int,
Price Float,
Qty * Price As Total
)
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May 20, 2015
I'm working on re-indexing a table using some commands from ALTER INDEX REBUILD from Microsoft. The indexes will be tested for threshold fragmentation. my plan is once the reindex is executed, a transaction backup will occur while controlling the size of the log file. The query impose time limitations or stop reindexing after the specified amount of time has elapsed.
my question,
1. How can I integrate a query which checks if transaction log is getting full and which runs a Tlog backup if over 70%
2. How do I impose time limitation?
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Sep 13, 2007
Hi,
Please, What s the differnce between a column that s a primary key and a column that s a "key/index with Isunique=true"?
Thanks a lot.
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Aug 14, 2007
Hi,Would like to know the performance differenece between Multi-columnIndex vs Single Column Indexes. Let's say I have a table with col1,col2, col3 along with a primary key column and non-indexed columns.In queries, I will use col1, col2, and col3 together and some timesjust one or two of these three columns. My questions is, should Icreate one index contains col1, col2, and col3, or create 3 seperatedcolumns. I.e. each column has its own index. Any performancedifference?Thanks a lot.
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Sep 21, 2000
When I select a fieldname in a db as a primary key this will keep the uniqueness of that fieldname, but how is that work when I select 2 fieldnames (in Enterprise Manager) and click on the Key it will mark them as my primary key, but I can insert duplicates values in either fieldname.
Can someone explain this to me.
Thanks
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Aug 7, 2007
hi
am new to sql...i need to write a query ..it is like two teams can play more than 1 game but on different dates..
so if i create the table like this
Create Table Games( TeamName1 char(30),
2 numGoals1 int,
3 TeamName2 char(30),
4 numGoals2 int,
5 play_date char(10),
6 primary key(TeamName1,TeamName2,play_date),
7 Check(TeamName1!=TeamName2)
8 );
this violates the constraint if i give the two teams on the same date..how to give the condition such that it checks for the violation of condition if the team names are interchanged.. for eg
if i give the values as
Insert Into Games values('chelsea',1,'arsenal',2,'17-1-2000');
and
Insert Into Games values('arsenal',1,'chelsea',2,'17-1-2000');
the above should violate the constraint ..how to do it
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Apr 24, 2008
Hello,
My company is upgrading one of our products; this involves some data migration and a question about existing indexes with uniqueness constraints has been raised. Here is the issue:
We have a database table with two particular columns that that we index with a uniqueness constraint. My question is: is the uniqueness constraint case sensitive?
For instance, if I have a database that is using a collation of SQL_Latin1_General_CP1_CS_AS. (case sensitive) and I insert data in these two columns as follows:
test
col2test
Test
col2test
would this uniqueness constraint be violated even though I'm using a case sensitive collation? I've done tests on this issue and I can't seem to insert this 2nd column; I'm just wanting to be certain that this is the case 100% of the time.
Thanks for your assistance,
Aaron
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Jul 23, 2005
Hello everyone, I am new to ERWIN and I need helps from the experts outthere.We are using ERWin 4.1.2771 and have reversed engineered some MS SQLServer 2000 databases.The problem we are having is that we have a FK on a column to a tablewhere the PK of the referencing table is on another column (such as anidentity column). We have a unique index on the column in the PK tableand SQL Server allows you to build a FK reference even though thecolumn is not defined as the PK.Does anyone know how to create this type of FK within Erwin?Thank You
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Jul 5, 2000
Hi,
Can anyone tell me the order in which uniqueness constraints on indexes are enforced vs. when triggers are executed ? I have a unique constraint on an index and a trigger on the column on which the same index has been created. When a row is inserted, the trigger checks if the value for that column already exists in the table - if not, it inserts the row as is, else it gets the max() val of the column (based on another key column) and increments it by one, then does the insert. Creating an index across the two works fine, but if I set the Unique Values property for the index, subsequent inserts bomb out - yet there aren't any duplicates in the final table, as the trigger ensures this. Anyone got any ideas on this? My deduction is that the uniqueness constraint gets enforced before the trigger gets executed, but at the same time this *seems* illogical, as the row has not been inserted into the table at the point where the trigger is executed.
Regards,
Jon Reade.
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Jan 22, 2014
OK - maybe my Google-fu is off today but I'm trying to find out if using a sequence table will provide values that are as unique as the GUID is supposed to be.The reason is that I'm building a DW from the ground up (they won't let me expense my booze which I think is grossly unfair ) and rather than using GUID it ~seems~ like a sequence table would give better results. My concern is that the values won't be unique across tables.
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Jul 20, 2005
Hi,First of all my apologies if you have seen this mail already but I amre-sending as there were some initial problems.This query is related to defining indexes to be unique or not andconsequences thereof.Some documented facts that I am aware of include1. Defining uniqueness allows optimiser to create optimal plans egselect based on keys in such an index allows the optimiser to determineat most only one row will be returned2. Defining uniqueness ensures that rule (business/Primary key) isenforced, regradless of how the data is entered.We have many cases where non unique indexes are defined. The approach todate has been that even though we are aware of some of the benefitsoffered by defining uniqueness , we have chosen not to add keys to nonunique indexes such that they become unique. The primary reason for thiswas that we did not want to make the keys comprising the indexesunnecessarily large and therefore ensuing consequences when DMLstatements are performed.However, I have concerns that having highly duplicate indexes can haveperformance impacts , including deadlocking. I am also aware Sybase usedto store duplicate values in overflow pages and therefore there wereperformance consequences. Could SQL 2000 have the same behaviour ?Thanking you in advancePuvendran*** Sent via Developersdex http://www.developersdex.com ***Don't just participate in USENET...get rewarded for it!
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Jun 17, 2008
So, I have this idea of a database design I was hoping to get some input on.
I usually go through the process of creating a separate column for identity, like an auto-increment integer which serves as a context specific ID that easily can be passed around. However one of the short-comings I've come to realize is that the integer is just that, unique to the context and requires context information to make sense.
I'm pounding the idea of creating a separate table whose sole purpose is to provide global (database wide) unique IDs. As such each row in a table can still have an ID but instead of being tied to a specific context it will always make sense within the application. A foreign key constraint can ensure that and a relation.
Now, with a global ID which I can create FKs to, I don't have to create a separate table for relations between entities and can have relations through these global IDs and I think that's a good thing because if there are many relations between many entities they don't have to be defined more than once. There is also a single "hub" where all relations fit which will allow me to access most information through some relatively simple joins.
My concerns are performance and Linq to SQL implication. I'm worried that Linq to SQL might start pulling an excessive amount of data and I'm worried that the practicality of such a design might hurt the long running of the application development process.
But I'm surprisingly interested in what it could mean for a more ubiquitous view of data and tagging. Basically a way of any data to have relations to any other data through this yet simple design decision.
If you think this is a good idea or see no particular problem with, please let me know! If you think there's problems with my idea, please motivate your critic but do tell me what I should look out for, or if you know of any better approach to my idea of being able to look at the data through some more common mechanism (which applies to all tables and the entire database mostly from a programming perspective).
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