A database structure that can improve the speed of queries at the cost of disk space and slower inserts/updates. It stores a copy of one or more columns but structures the data differently to allow for faster access.

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1answer
302 views

Design Tagging module in the database

I've a database system which we want to define tags for many tables into it. For example I've videos, photos, ... different entities that we wish to make them taggable. The tags could be anything. By ...
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1answer
1k views

What is Sql Server Clustered Index in Oracle terminology

A clustered index in sql server like a dictionary or telephone directory. A,B,C,D it goes on. If you look up with a name Ozgur you start O then z etc. I would like a simple explaination for this ...
11
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4answers
473 views

Determining that Indexes on a table are unused

I’ve been running this script to try to find extraneous indexes select o.name as TableName, i.name as IndexName, p.reserved_page_count * 8.0 / 1024 as SpaceInMB, s.* from ...
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5answers
595 views

Are these good indexing guidelines?

I use indexes regularly but it's still hard for me in certain conditions to know if they are helping or hurting. There are a few guidelines I follow, but I am not sure if they are good nor am I sure ...
5
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1answer
566 views

Tuning queries and indexes using index analysis tool

I've been pointed to this script from several places which apparently helps with designing indexes in Microsoft SQL Server: http://indexanalysis.codeplex.com/ The problem is I'm using Sybase ASA 11, ...
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1answer
905 views

Does composite cluster index affect performance of seek/scan non-cluster index which is part of the composite?

I have bank transaction table with columns Division Brcode TrDate ProjectCode Accountnumber EffectiveDate DrCr Amount EndBalance In the other table the Brcode itself is unique and is assigned under ...
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2answers
2k views

How can an identity primary key index become fragmented?

From what I understand about index fragmentation, this should not be possible. The cases I have found in my databases are non-clustered. Example: ALTER TABLE [dbo].[ClaimLineInstitutional] ADD ...
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2answers
1k views

Rebuilding Index - sort in temp db

What is the significance of SORT_IN_TEMPDB when working with indexes on a table of significant size (20GB plus)? Where else does sorting take place?
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1answer
805 views

How to prevent big performance impact during index creation

I have an existing database that is missing some indexes. When I tried creating some the database server really suffered in CPU usage during index creation interfering with the regular workload. Is ...
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2answers
1k views

Is there any index with O(1) complexity for lookup in PostgreSQL?

Is there any index type in PostgreSQL that gives O(1) complexity for lookups? on strings?
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1answer
1k views

Using FORCE INDEX

I was in a presentation recently given by a Facebook MySQL engineer and he mentioned there that using FORCE INDEX reduces I/O. It was something to do with the MySQL Query Optimizer not needing to go ...
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2answers
204 views

In MySQL, should I add an index even if the query that scans the table is only ran once a month?

Concretely, is it worth it to add an index to a query that scans the table of a mysql database, even if that index would only be used once a month? For example, having a users a table and then ...
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5answers
506 views

Indexing from start or when performance problem arises?

My question is regarding use of indexes. Should I start indexing right from the start or when performance problem arises? We can also create temporary index while executing a query. What are the ...
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2answers
183 views

How to index this table (a_level, b_level, item_id)

I have a table of items, each of it has an a_level, b_level, and an item_id. Any b_level is dedicated to only one a_level (example: b_level 14 is "child" of a_level 2 only) Lets say we have million ...
11
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3answers
331 views

Included Column versus Filtered Index

We currently work with table named tb_tranfers. This table has 40 million rows and is ~26 GB in size (11 GB data, 15 GB indexes). 10 to 15% of the rows are soft-deleted rows (DeletedDate is not ...
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1answer
387 views

How SQLite index ID (or line number)

SQLite is based on a flatfile, and store virtual tables in a flatfile (I think based on offset, correct me if I'm wrong). But how it index the Primary Key (ID), which I think is identical to line ...
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2answers
2k views

How does Oracle handle composite index lookups?

MySQL cannot use a composite index in a lookup in which the WHERE condition doesn't include the columns forming a left-most prefix: MySQL cannot use the index to perform lookups if the columns do ...
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4answers
3k views

What impact do indexes have on the performance of table modifications? [duplicate]

I have always wondered what the effect indexes have on table modification in SQL Server. Will modification of a table will be slower with an increased number of indexes applied to that table? My gut ...
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5answers
13k views

Working of indexes in PostgreSQL

I have a couple of questions regarding working of indexes in PostgreSQL. I have a Friends table with the following index: Friends ( user_id1 ,user_id2) user_id1 and user_id2 are foreign keys to ...
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3answers
22k views

What is the default order of records for a SELECT statement in MySQL?

Suppose you have the following table and data: create table t(k int, v int,index k(k)) engine=memory; insert into t values(10, 1), (10, 2), (10, 3); When issuing select * from t where k = 10 with ...
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3answers
10k views

Best of MyISAM and InnoDB

Is it possible to make InnoDB to use indexes same as MyISAM instead of clustered index due to limitation of RAM while getting benefit of its concurrency performance?
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1answer
212 views

Strictly only RAM matters?

I have to work on a project which would have a extra large table with billions of records but only two fields one is id and another is text. And id would be set to BIGINT and PK then if 8+2 (extra 2 ...
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3answers
3k views

When do hash indexes become reasonable?

MySQL natively doesn't support hash indexes. So, making a pseudo hash column and creating an index on a hash column needs some thinking. And it seems to be widely understood that if the text field is ...
2
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2answers
466 views

What does “GIN doesn't support full index scans” mean?

I'm a RDBMS newbie and I have a PostgreSQL database of more than 50 millions lines, growing everyday. There is a column 'text', which contains human-generated text of around 20 words. I need to be ...
7
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2answers
276 views

Why is Oracle using the index here?

Name Null Type -------- -------- --------- ID NOT NULL NUMBER(4) GROUP_ID NUMBER(4) TEXT CLOB There is a btree index on group_id. Here's how many ...
2
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2answers
345 views

Indexing of Data Warehouse tables?

Maybe I have misunderstood something but I can recall reading an article which said that there is no reason to create non-clustered indexes on very large data warehousing tables? That is because ...
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2answers
8k views

How to know when/if I have too many indexes?

Running Microsoft SQL Server Profiler every now and then, it suggests me with a bunch of new indexes and statistics to create ("...97% estimated improvement..."). From my understanding every added ...
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1answer
179 views

What are hypothetical indexes?

They seem to be created by tools like DTA. For practical purposes they could be deleted, ignored or chosen to be created, but until then, they have no direct influence on the database.
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3answers
26k views

Why is my database still fragmented after I rebuilt and reindexed everything?

I have a database which I tried to defragment all the tables at once by running this T-SQL: SELECT 'ALTER INDEX all ON ' + name + ' REORGANIZE;' + CHAR(10) + 'ALTER INDEX all ON ' + ...
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1answer
132 views

Reasons against using local indexes

For Oracle 10g and above: except in cases where a local index cannot be used and a global index is needed (e.g. unique constraint), is there any reason to favor a global index over a local index?
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3answers
2k views

Indexing - Uniqueidentifier Foreign Key or Intermediary mapping table?

Looking for some expert views on this guys - I'm not a DBA by trade so would appreciate any advice. Comments on the rest of the schema aren't required as it is purely fabricated to illustrate my ...
2
votes
1answer
6k views

What I can do to speed up Key Lookup in my Query

I am using SQL2005 and against them I calling query simila to this declare @art table (id int primary key, naziv varchar(35) null, sifra varchar(15) null, jm int null); insert ...
2
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2answers
600 views

Full Name search query

We currently have a solution for this in production, but it's pretty bad. I'd like a fresh perspective on it please. We have a PERSON table with an ID, LAST_NAME, FIRST_NAME, MIDDLE_NAME, and ...
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2answers
645 views

FBI on function with concatenated string

I have an index in place (from days of old) that I'm curious about. It's on a basic person table and the function is upper("LAST_NAME"||','||"FIRST_NAME"||"MIDDLE_NAME"||"SUFFIX_NAME") When trying ...
6
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3answers
308 views

When you select from a table on an indexed column and order by that column in the opposite direction of the index, does the index help

Let's say I have a large table of transactions with a date field and an index on that field in ascending order. If I select that field from the table and order by in reverse order is it able to ...
5
votes
1answer
2k views

SQL Server 2008 R2 reindex job reorganise getting stuck

I am currently experiencing this job getting stuck in my nightly maintenance solution - ALTER INDEX [PK_ThirdPartySettleCalled] ON [evo_archive].[dbo].[ThirdPartySettleCalled] REORGANIZE WITH ...
2
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1answer
379 views

Optimising a sql correlated subquery statement

I am updating a column on tableA with data from tableB like this: update tableA set bKey = select bKey from tableB B where B.colB = tableA.colB bKey has a unique index on tableB. Which is the ...
4
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2answers
148 views

Performance of SQL Server indexing

I want to see the performance differences between an indexed vs non-indexed column when running the same query. The table I've created (FileCollection) is very simple and has the following 3 columns ...
3
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1answer
214 views

Minimum rowcount for filtered index?

Creating an index always has trade-offs. Whenever you insert, update or delete, it has to perform those operations on the index as well. This is all pretty commonly known. But with the advent of ...
15
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2answers
6k views

How to create an index to speed up an aggregate LIKE query on an expression?

I may be asking the wrong question in the title. Here are the facts: My customer service folk have been complaining about slow response times when doing customer lookups on the administration ...
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3answers
77 views

SQL Server - Index Including PK

Lets assume we have a table as follows: PK -- nonclustered primary key Col1 -- unique clustered Col2 Col3 Is this index: nonclustered index on (Col2, Col3) any different from this index: ...
30
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4answers
29k views

When should I rebuild indexes?

When should I rebuild the indexes in my relational database (SQL Server)? Is there a case for rebuilding indexes on a regular basis?
4
votes
2answers
901 views

Index Generation in Postgres

We have a database with a single table made up of around 700 million entries. We update the database by adding new entries on a server then transfer the server to the production server using pg_dump: ...
3
votes
2answers
133 views

What would be the best way to model my simple table?

What would be faster: searching for the right row through a table with 17 different columns, each with a tinyint value of 1-4? Or, searching for the right row through a table with only 1 column with ...
8
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1answer
816 views

The use of NOT logic in relation to indexes

According to Microsoft's book on database development Exam 70-433: Microsoft SQL Server 2008 Database Development: Neither leading wildcard characters not NOT logic allow the query optimizer to ...
5
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1answer
62 views

SQL Server 2008 Index

What would be the best index(es) to add to the tables in order to make this query as fast as possible. The sd.incidents tables is about 2.5M records, problems about 8K, and changes about 120K. select ...
2
votes
2answers
482 views

Check Index Fragementation Query

I'm completely stumped. I'm a relatively new SQL Server DBA so I'm at a loss with the following situation; hoping maybe someone had an idea. I have a new production SQL Server (Windows Server ...
20
votes
7answers
893 views

Where can I find some guidance on index strategies?

Most of us will probably agree that using database indexes is good. Too many indexes and performance can actually be degraded. As a general rule, which fields should be indexed? Which fields should ...
3
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3answers
982 views

Does this computed CHECKSUM() index design make sense?

I have come across what looks to me like a slightly odd pattern in a SQL Server 2005 database I'm taking care of, and was wondering whether it's just me, or whether it really is odd. There are a ...
2
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1answer
124 views

Index issue on order by column while applying Union all

I have two tables with 6 columns in 1st table and 6 in the second one. I have to combine the result of these two tables in order to make them in one set. Below are the structures of my tables: CREATE ...