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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719 views

InnoDB - Use combined index with primary key on GROUP BY

As far as I know, an InnoDB index always contains the primary index. I cannot get the following to work: SELECT t1.a FROM table_1 t1 LEFT JOIN table_2 t2 on t1.id = t2.refid WHERE t1.b = 99 GROUP ...
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2answers
1k views

Filtering data ordered by rowversion

I have a SQL table of data with the following structure : CREATE TABLE Data( Id uniqueidentifier NOT NULL, Date datetime NOT NULL, Value decimal(20, 10) NULL, RV timestamp NOT NULL, ...
3
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1answer
203 views

I have Fragmented Index on a empty table!

I ran the following query on my database to identify the fragmented indexes. However I surprised when saw the Indexes belong to some empty tables among the highly fragmented indexes! How can it be ...
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2answers
1k views

How does compound index help speed up query?

Say we have a bunch of column in mysql table. Latitude Longitude Say we make an index (Latitude and Longitude) Well, the index will sort by Latitude first and IF the Latitude is the same it'll sort ...
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Does having an index on a VARCHAR column with a lot of very similar starting values have bad performance

We seem to be having quite unusual bad performance on queries that use an index. for example the table looks like PK BIGINT ID VARCHAR(50) Col1 Col2 etc So we need to insert a row in the ...
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1answer
1k views

Does MySQL have a limitation of one index per query?

MySQL supports spatial index. However, all the spatial index can do is find points in a box. It can't do fancy stuff like find the nearest 1000 points, etc. I think, and I don't know where I went ...
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3answers
630 views

SQL Server : explicitly create an index on a primary key and unique fields

UPDATED: I'll make the question clearer as the first answer isn't quite what I was looking for. How can I execute this create table statement and ensure that the two automatically created indexes ...
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4answers
610 views

Can I reorganise index on a sql server 2005 database without performance hit on production server

I would have preferred to run online index rebuild instead but our production sql server (2005) is standard edition. Hence I think I am left with reorganising index and update statistics after that. ...
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2answers
153 views

Unique Contraint/Index Based On Values

I have a table that has the following column definitions: ID (INT, PK) Name (VarChar) Active (Bit) Bunch_of (Other_columns) Question: I want to have a Constraint on Name/Active such that we can ...
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37 views

How does MySQL 5.1 use indexes?

I've read the docs for MySQL v5.1.x on how about the indexes are used, but I'm not sure I understood it properly. Suppose having the following MySQL table: CREATE TABLE IF NOT EXISTS ...
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2answers
1k views

How can I optimize this mySQL table that will need to hold 5+ million rows?

The table has about 12 rows. Indexes: idint(11), Unique, auto-increment, primary ATTACHMENTIDvarchar(14), Unique MLSNUMBERbigint(20) POSITIONint(10) FILETYPEvarchar(32) I'm doing an extended ...
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464 views

Using indexes to create multiple relationships to a table in order to enforce data integrity and add meaning

I'm working on an inventory database that uses supertype/subtype model. My question regards creating multiple relationships with the same tables using the primary key and composite indexes that also ...
5
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1answer
439 views

SQL Server: Effect of Setting These Index Options

A reindexing script was recently run in our dev environment that set ALLOW_ROW_LOCK = FALSE and ALLOW_PAGE_LOCKS = FALSE on all the indexes in the database. This was done while testing new reindexing ...
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2answers
2k views

difference between having many non clustered index with single columns and with combination of many columns

Folks I am a newbie to DB design stuffs. I am wondering what would be the difference and performance difference between having designed many non clustered index with single columns and non ...
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1answer
298 views

Should indexes automatically be placed into their own bufferpool?

We work with DB2 LUW (specifically we are currently on 9.7 FP4) running on AIX. Per best practices from IBM, they recommend that when you build a table, you place the data, the indexes, and LOBs/LONG ...
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2answers
623 views

Does a cluster index provide more benefits than pre-sorting the load file and creating non-cluster index?

Informix 11.70.TC4DE: CREATE TABLE cluster_tbl ( fk_id INT, data CHAR(2048) ); LOAD FROM "presorted.ld" INSERT INTO cluster_tbl; CREATE UNIQUE CLUSTER INDEX cl_idx ON cluster_tbl(fk_id); ...
2
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1answer
248 views

MySQL: Very slow query, not using index, no joins involved

I am running what I think is a very simple query: SELECT SQL_NO_CACHE m.mbr_nbr FROM tran.member m WHERE m.cardnbr = 000099999930 The table member is a poorly written one, with 133 columns and ...
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2answers
671 views

Reorganize Indexes T-SQL

I'm moving a database to SQL Azure and with that I lose the maintenance plans so I am going to use a Worker Role to schedule them. When I open the properties of the Rebuild Index Task and click on ...
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1answer
94 views

Where does it make sense to store Indexes for partitioned tables?

Prior to table partitioning, all the indexes were stored on a separate drive, per this question. Now that I partitioned a couple of tables, SSMS is offering to store indexes in the partition scheme. ...
2
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1answer
4k views

Do you set an index on JOIN clauses or where clauses, or both?

Say my query looks like: SELECT t1, t2 FROM t1 LEFT JOIN t2 ON (t1.id = t2.id AND t2.userid = @userid) WHERE t1.enabled = 1 AND t1.startDate <= ??? AND (t1.counter = -1 OR ...
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1answer
122 views

mysql dummy where check to utilize multi column index

I have multi-column index on col1,col2. Both columns are unsigned int with values 1 or greater. I want WHERE col2=100. I write WHERE col1>0 AND col2=100. The query should now use my index. Does ...
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2answers
1k views

SQL Server 2012 - Frequent SELECT and UPDATE on bit column. Index doesn't help

I have a SQL Server table with about 2 million rows in, this table stores short textual documents. Here's my schema: CREATE TABLE Documents ( documentId bigint IDENTITY NOT NULL, content ...
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3answers
3k views

InnoDB vs MyISAM with many indexes

I am not sure if there is a right or wrong answer to this question, as I suppose it severely depends on the situation, but for the sake of a mental exercise, I'll go ahead and ask it anyway: I have a ...
0
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1answer
59 views

Is index like key(timetime) usable when we query: SELECT * … ORDER BY timetime DESC

When we index a timestamp field like timetime. Can we use it for ORDER BY timetime DESC or is it just usable for ORDER BY timetime ASC OR ORDER BY timetime? Does mySQL use this index when doing vise ...
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1answer
1k views

How does SQL Server choose an index key for a foreign key reference?

I am working with a legacy database that was imported from MS Access. There are about twenty tables with non-clustered, unique primary keys that were created during the MS Access > SQL Server upgrade. ...
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2answers
5k views

SQL Server 2008R2 - Why is my index not used

I have a table defined in the following way: CREATE TABLE [dbo].[MyTable] ( [MyTable_ID] [int] IDENTITY(1,1) NOT NULL, [COLUMN_WITH_DATA] [varchar](128) NOT NULL, [COLUMN_A] [varchar](128) ...
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2answers
106 views

SQL and Multiple Indexes

Consider the following table: i | a | b | c -------------- 0 | 1 | 2 | 3 1 | 4 | 5 | 6 2 | 7 | 8 | 9 3 | x | y | z The table, in the end, will have several thousand rows, and even more columns then ...
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4answers
6k views

Benefits of BTREE in MySQL

What are the pros and cons of using a BTREE index in MySQL, regarding query speed, disk storage and memory usage? Does BTREE provide easier iteration in increasing order ? What kind of queries would ...
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1answer
2k views

How can I tell if an index is being used to sort in MySQL?

I have a query with an ORDER BY clause which uses a column which is the last column on an index which is being used in the WHERE clause, essentially of the form: SELECT cols FROM tables WHERE ...
5
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1answer
617 views

Index defrag takes forever to run

We have an Agent job that runs every morning at 2a.m. to defrag the top 5 biggest tables. Usually it takes around 20 mins to complete. It has stayed this way for several years. However, recently (last ...
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2answers
1k views

Should a table have a clustered index even if it doesn't have appropriate fields for it?

If you have a table without a good candidate field or fields for a clustered index (stable, sequential), is it better to have a clustered index on a bad field or is it better to make all table indices ...
3
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1answer
272 views

Adding new key(s) to enable partitioning, INSERT performance?

I have a table to storage GPS coordinates with multiple (~30) inserts per second (from 50 different devices) during 12 hours per day, so the table is growing fast, to improve the SELECT speed I was ...
3
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2answers
3k views

Postgres primary key sorted in the reverse order. Will it use the index efficiently?

My Rails database is backed by Postgres database. As you may know, each table in Rails gets assigned a primary key which is of Integer type and is indexed. My list views show records in the reverse ...
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2answers
1k views

Slow ORDER BY with LIMIT

I have this query: SELECT * FROM location WHERE to_tsvector('simple',unaccent2("city")) @@ to_tsquery('simple',unaccent2('wroclaw')) order by displaycount I'm happy with it: "Sort ...
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2answers
909 views

How to move all non-unique and non-clustered indexes to a different filegroup?

I want to move all indexes to a separate hard drive. To that effect, I created a new filegroup, then added a new file to it (e.g. alter database foo add file(...) to FileGroup). Now I want to move ...
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2answers
4k views

How can primary keys in a Netezza table be indexed?

What is the best way to index a Netezza fact table with lots of primary keys. For now, let's suppose we have 10 primary keys. This table is mainly used to store meta data about our database. ...
2
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1answer
2k views

creating an index for varchar column greater than 900 bytes

I have a var char column in SQL Server 2008 which is usually less than 100 bytes but in some cases can be huge up 5607 bytes. I need to index it, and I can't because the max index size in SQLServer is ...
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1answer
112 views

How can I reset the index of the rows?

I would like to select and insert data from an old table to the new table: CREATE TABLE test2 LIKE test1 INSERT INTO test2 SELECT timestamp, datenum FROM test1 WHERE datenum>=23 and ...
2
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1answer
2k views

postgres composite index design

In my rails application using the Postgres database, I have a table called tw_schedules which belongs to a scenarios table (one scenario to many tw_schedules). In addition to the scenario_id foreign ...
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2answers
1k views

How to prevent daily index fragmentation of 99%

I have a highscore table for 100.000 players that is being inserted into 2 times a day with one record per player. At the end of the day the index fragmentation for the indexes in that table is 99%. ...
7
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1answer
713 views

computed columns, index, clustered index and covering index?

We all know the we can only have one clustered view per table, cool. But apparently you don't have values of computed columns on leaf even when using a clustered index and they are computed each time. ...
2
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1answer
113 views

Are two indexes needed?

Our MySQL database will contain an encyclopedia. The encyclopedia will be shown in pages where every page contains entries starting from a letter. Which indexes should I use? Should I have two ...
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1answer
137 views

SQl code performance

What measurement do you know if this sql code is efficient based on execution plans? How do you know if this sql code is efficient based on execution plans? SELECT [CustomerID], ...
3
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1answer
4k views

Oracle 11: Change global index to local on huge production table

I have big partitioned table with global index. My case is drop old data from archived partitions. I can't simply drop partition because i have global index. So I have idea to use INVISIBLE local ...
3
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2answers
525 views

What exactly is “pinning” in relation to indexes?

When one talks about "pinning" in indexes, what exactly is this? Is there some other word/term I can search for, as google has not provided any solutions. It is part of a test question, where ...
2
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1answer
147 views

Should I use an index or a hash function on a primary key if I have 100000 rows of data?

I have a table named PRODUCT that has 100,000 rows. I was wondering if either indexing, or a hash function on the primary key would result in better performance. I was also hoping someone could ...
2
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1answer
3k views

SQL Server Rebuild/Reorganize Fragmented Indexes causes CRC error or consistency errors

In our test lab I've been experimenting with different jobs to keep our critical indexes from becoming too fragmented. I'm currently using the approach described here: sys.dm_db_index_physical_stats ...
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2answers
10k views

Why index REBUILD does not reduce index fragmentatation?

I have used ALTER INDEX REBUILD to remove index fragmentation. In some cases REBUILD does not seem to remove this fragmentation. What are the reasons why REBUILD does not remove fragmentation? It ...
4
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2answers
198 views

Does a dual key or single key lookup perform better on a table with a lot of data?

We have table where rows unique between 3 columns. GroupA, GroupB, ProductID. GroupA & GroupB are used in combinations to Group sets of ProductIDs and will always be used to lookup sets of ...
12
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3answers
1k views

Can spatial index help a “range - order by - limit” query

Asking this question, specifically for Postgres, as it has good supoort for R-tree/spatial indexes. We have the following table with a tree structure (Nested Set model) of words and their ...