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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375 views

What happens when we add an index to an existing table with a large amount of data?

I've a table which will contain around ~15 Million records. Now I need to add an index to the table. Adding an index will take some time to update every entry in the table. I'm quite confused ...
6
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1answer
163 views

PostgreSQL partial index unused when created on a table with existing data

In PostgreSQL 9.3, I am attempting to create an efficient index on a rarely-used (0.00001% of total records) boolean column. To that end, I discovered this post on SO: http://stackoverflow.com/a/...
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2answers
3k views

Pagination with PostgreSQL 9.3: counting number of pages

I'm implementing pagination and sorting of rows in, let's say, products table, using multicolumn index on category, score and id. -- index create index category_score_id on products(category, score, ...
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1answer
877 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

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 ...
6
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1answer
8k views

How to make a union view execute more efficiently?

I have a large table (tens to hundreds of millions of records) that we have split for performance reasons into active and archive tables, using a direct field mapping, and running an archive process ...
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2answers
3k views

Dropping and recreating indexes for performance reasons?

I'm maintaining Somebody Else's Code. There's a stored procedure that's run once a day or week (depending on config), that migrates a bunch of records from an active table to an archive. But it's ...
6
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1answer
2k views

Estimating impact of indexes SQLite database size

I'm trying to estimate the database size (on disk) for a SQLite DB that includes a number of indexed columns. These columns are of (SQLite) type Integer and String. It's straightforward enough to ...
6
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1answer
115 views

Index Allocation Maps

I am a developer reading the book "Querying Microsoft SQL Server 2012." I have come across the following diagram: Why are the pages in the first two rows of the diagram (row 1 starting: 1:174 and ...
6
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2answers
968 views

Optimizing WHERE condition for TIMESTAMP field in MySQL SELECT statement

I am working on a schema for an analytics system which tracks usage times, and there is a need to see total usage time in a certain date range. To give a simple example, this type of query would be ...
6
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1answer
12k views

Optimizing large database query (25+ million rows, using max() and GROUP BY)

I'm using Postgres 9.3.5 and I have a large table in the database, currently it has over 25 million rows and it tends to get even larger rapidly. I'm trying to select specific rows (all unit_ids with ...
6
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1answer
170 views

Ok to drop indexes on FK's if they have no stats in the DMVS

I have used the well known query below from Kevin Kline to check for unused indexes. Several indexes created on Foreign keys returns no read stats, only writes. Are you 100% safe to drop these ...
6
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1answer
587 views

Will a clustered index improve performance of updates performed sequentially on that clustered index?

I know indexes reduce data modification performance, but I have a task where (almost) all updates are done on items in a sequential order. Would a clustered index improve or reduce performance in ...
6
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1answer
2k views

Oracle concatenation of queries and function index usage

I have a problem with something I can't understand about indexes in Oracle 11g. We can create test data with: create table test2(field1 varchar2(100),field2 varchar2(100),field3 number,field4 ...
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3answers
2k views

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 ...
6
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1answer
1k views

How can I get status messages during a large re-indexing operation with MySQL 5.5?

I get large data transfers periodically that I used to completely replace the contents of a MySQL table. Each time I do this, I truncate the table, disable keys, add several million rows of data, and ...
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1answer
503 views

Can filtered indexes help improve queries that are based on a time entered or should this be avoided?

I'm just learning about the new filtered indexes in MS SQL 2008 and I'm trying to understand where they would hurt and where they would help. I can see that adding a filtered index to an employees ...
6
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2answers
437 views

Over 99 million records with geography column & spatial index - VERY VERY VERY slow queries!

I’ve been working with SQL Server for a long time but have only recently encountered the need to work with spatial data. I have come into an environment that uses it pretty heavily and my first real ...
6
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1answer
644 views

Timestamp-based index

I have a big database (200GB+) that contains some log info. And I want to speed up SELECT queries and stored procedures. I have a table with a GeneratedOnUtc datetime column, and have a non-clustered ...
6
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1answer
2k views

Advisability of using STATISTICS_NORECOMPUTE

I've recently become involved in maintaining a set of databases with some interesting index problems. One of the ones that aggravates me the most is the differences in the indexes between development,...
6
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1answer
382 views

Landed as BI, but databases are a big WTF, what to do?

Maybe a duplicate, but I believe my case is a bit different. From one of the answers I got to this post on SQL Server Central that also comes handy too but is not quite the same scenario: 9 Things to ...
6
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2answers
857 views

SQL Server: Create New GUID Values for Existing Index

I have an existing table with about 6 million rows. The relevant columns are: ID int not null PK Key uniqueidentifier not null Read/write on this table by Key lookup is probably something like 100 ...
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2answers
4k views

Bitmask Flags with Lookup Tables Clarification

I've received a dataset from an outside source which contains several bitmask fields as varchars. They come in length as low as 3 and as long as 21 values long. I need to be able to run SELECT queries ...
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2answers
1k views

Recreate Indexes on 1 billion record table

I have a table with over 1 billion records and it has 6 indexes (including Clustered index (ID)). I need to partition this table on a new Clustered index with date column. I have just enough space (...
6
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1answer
487 views

Permission to create Spatial Index

Permissions required to create a Spatial Index on a table, for this BOL says: Requires ALTER permission on the table or view. User must be a member of the sysadmin fixed server role or the ...
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1answer
3k views

Schema design: Use of association (aka: bridge/junction) table vs foreign key constraint with composite index containing a non-key field

This is an inventory database for IT assets. The models used are trimmed in order to focus on the problem at hand. Using SQL Server 2008. Thanks for taking the time to read and for any input you can ...
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1answer
520 views

Can spatial index be a part of a multiple columns index?

This manual over here is extremely unclear and doesn't even provide some sample SQL statements: http://dev.mysql.com/doc/refman/5.6/en/column-indexes.html Another way to rephrase the question is the ...
6
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1answer
339 views

Performance of query with a range condition and order by

We have the following table (in SQLite on Android) which a tree structure (Nested Set model) of words and their frequencies: lexikon ------- _id integer PRIMARY KEY word text frequency integer ...
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1answer
2k views

Reindex Task Failing Randomly [closed]

We use the built-in maintenance plan to reindex (and backup, etc.) our production SQL Server. The problem we are currently having is the reindex task started failing randomly this week after months ...
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3answers
828 views

Is a surrogate key better than a natural key in this case

I copied this code from here: CREATE TABLE records( email TEXT REFERENCES users(email), lat DECIMAL, lon DECIMAL, depth TEXT, upload_date TIMESTAMP, comment TEXT, PRIMARY ...
5
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3answers
113 views

Interpreting an execution plan

I need some help analysing some simple t-sql execution plans. I have a table [User] with the following 3 columns: Id(Primary Key), Username(nvarchar(50)), FirstName(nvarchar(50)) I have Created an ...
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4answers
5k views

How to check for existence of an INDEX on a column independent of used SQL database

Is there are unified way of how to check for the existance of an INDEX for a given column irregardless of the actual SQL database system used? For MySQL one could for instance check for the existance ...
5
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1answer
784 views

Don't rebuild indexes < 1000 pages - then why bother having them?

Microsoft recommends not bothering to rebuild indexes that have less than 1,000 pages (from memory I think it's because they are so small that they will be held in RAM). If I'm not rebuilding them, ...
5
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2answers
4k views

Should I refresh query plan cache

Please let me explain my problem and situation: I have a web application - MVC3, MSSQL Server 2005, LinqToSQL. It has been running great until one fine morning I pushed a lot of rows to a table that ...
5
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3answers
138 views

Dynamic temporary index creation

In my undergrad databases course, my professor mentioned that some DBMS software is so advanced that it can detect when a long-running query would benefit from an index. The DBMS can then create that ...
5
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3answers
2k views

How can I force MySQL to IGNORE ALL indexes?

I have read articles about FORCE index, but how can I force MySQL to IGNORE ALL indexes? I tried SELECT * FROM tbl IGNORE INDEX(*), but I was not successful. As for why I (and others) need to do ...
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1answer
2k views

Understanding “bitmap heap scan” and “bitmap index scan”

I'll try to explain my misunderstandings by the following example. I didn't understand fundamentals of the Bitmap Heap Scan Node. Consider the query SELECT customerid, username FROM customers WHERE ...
5
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4answers
474 views

Why index is not used with order by?

I trying to get info about why MySQL does not using my index when I create a inner join and trying to ORDER BY on the end. I have my SQL query here: SELECT * FROM product p INNER ...
5
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3answers
240 views

Shrinking database which is not having any insert/update

We have a process of archiving wherein we take the backup of current database and restore it as xxx archive database. Now this database contains previous data and will not have any insert/update/...
5
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2answers
140 views

Confused about why a particular index is being used

I have a table (with 170M rows) that looks as follows: CREATE TABLE [dbo].[Panel] ( [SubId] [varchar](15) NOT NULL, [LineageId] [int] NULL, [Buck] [varchar](20) NULL, [Lot] [varchar](...
5
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1answer
3k views

How to create an index on an integer json property in postgres

I can't figure out for the life of me how to create an index on a property of my json column which is an integer. I tried it this way (and also dozens of others) CREATE INDEX user_reputation_idx ON ...
5
votes
1answer
9k views

How do I alter index rebuild an entire database?

I want to reorganize the indexes of all tables in my SQL Server 2008 database, named 'db'. I try the following command: ALTER INDEX all ON db REBUILD And I get the following error: Cannot find ...
5
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1answer
774 views

Which fillfactor is used by ALTER INDEX REBUILD?

From technet I got the impression, that I either have to explicitly set the wanted fillfactor or when I do not specify it, the default fillfactor 0 is choosen. For tables I know to get rows added ...
5
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2answers
732 views

If I update a column record in a table, will indexes that do NOT have this column in it be affected?

In terms of performance if I have a table like so: CREATE TABLE [TESTDATA].[TableA]( [Col1] [nchar](5) NOT NULL, [Col2] [nchar](2) NULL, [Col3] [float] NULL CONSTRAINT [TableA_PK] PRIMARY ...
5
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1answer
4k views

How are multiple indexes used in a query by MySQL?

Imagine a table where there are separate indexes on columns a and b. The query runs somewhat like this: SELECT col1, col2 FROM <table> WHERE a = 'value_1 AND b = 'value_2'; Now, does this ...
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2answers
172 views

Are existing entries immediately included into a newly created index?

Suppose I have a table Stuff with a column City and no indices including that column. I populate the table. Then I decide to create an index: CREATE INDEX [StuffOnCityIndex] ON [dbo].[Stuff](City ASC)...
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1answer
90 views

Conditionally add an index to a temp table

I have a stored procedure that looks something like this: SELECT columnlist INTO #temptable FROM Table JOIN lotsofothertables WHERE severalconditions UPDATE anothertable SET column = #temptable....
5
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1answer
186 views

How to index for inequality queries?

I have query that is excluding data based on the value of a float column select * from My_Table where my_Float_column != 0 and my_Float_column is not null I don't want to index a float type if I ...
5
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2answers
517 views

How to make this query use my multicolumn index?

Currently, I have a view which is defined like this: View "public.customer_list" Column | Type | Modifiers | Storage | Description -----------+---------...
5
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1answer
168 views

Is it possible to get seek based parallel plan for distinct/group by?

An example from this question shows that SQL Server will choose a full index scan to solve a query like this: select distinct [typeName] from [types] Where [typeName] has a non-clustered, non-...