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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3
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3answers
5k views

Nonclustered index is faster than clustered index?

Both tables have same structure and 19972 rows in each table. for practicing indexing, i created both tables having same structure and created clustered index on persontb(BusinessEntityID) and ...
7
votes
1answer
1k views

Index usage stats DMV indicates no index activity

I'm trying to obtain information on indexes. According to several websites, the below TSQL query should join information on indexes to the indexes table, returning indexes and related information. ...
2
votes
2answers
2k views

Update performance: clustered versus covering index

I have a simple, 3-column table with about 50 million rows in it. This table gets about 5,000 inserts/updates per second, and perhaps 20 queries per second are executed against the table. The table ...
1
vote
5answers
7k views

What happens when we create index

What happens exactly when I create an index on the empid column of this employee table CREATE TABLE employee ( empid number(5), ename varchar2(30), sal number(10,2) ); Let's assume the ...
2
votes
1answer
1k views

Does the size of the primary key contribute to table size?

I have a table (InnoDB) with data length around 36G and index length 23G. It had a composite primary key across three columns. As an initial attempt to reduce the size of this table, I dropped the ...
2
votes
1answer
619 views

Why does selecting top 1 from composite index DESC also used to partition by month not select the top value?

We have very large database table that I need to select the value of the max id. Given the table size SELECT MAX(id) FROM tableA will not perform well enough. Table definition (with columns omitted ...
0
votes
0answers
105 views

How to/advice for hosting a multi-user database on the cloud with specific objectives

I have developed an application that users will be able to download and create an account with through our company. This application will always be connected to the internet. I have been testing the ...
2
votes
1answer
628 views

Rebuild an index while it is being referenced in Oracle

I have come across many articles on this site and on Tom Kyte's blog on the how, whys and whens of Re-building indexes. Note that this question is about whether I can rebuild when there are concurrent ...
1
vote
1answer
292 views

Updating an FTS indexed column returns “Invalid InnoDB FTS Doc ID”

Environment: Ubuntu 12.04 (and 13.04) MySQL 5.6.11 I have a table which has a full text index on it (real table has much more columns and rows): DROP TABLE IF EXISTS articles; CREATE TABLE ...
5
votes
2answers
652 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
votes
2answers
218 views

Indexing strategy for dynamic predicate

Assume SQL Server 2012 Standard edition. My database has a table with 500 million rows. The table has about a dozen columns, none of which are very wide (some varchar(100)'s and some ints). The ...
3
votes
1answer
1k views

Index on foreign key makes query extremely slow

We are recently experiencing a tremendous query slowdown with spilled over temp tablespace. A specific query causes this problem. The queried table (table3) has an indexed PK, three FK with indexes ...
21
votes
6answers
3k views

Why don't databases create their own indexes automatically?

I would have thought that databases would know enough about what they encounter often and be able to respond to the demands they're placed under that they could decide to add indexes to highly ...
0
votes
1answer
62 views

MYSQL - Using simple inventory number convention as Primary Key

I have an inventory with three numbered groups like so: Group 1: 0-999 Group 2: e0-e999 Group 3: v0-v999 Can I simply make a one-column table to store this information and make that column the ...
1
vote
4answers
1k views

MySql Order by isnull() Performance Problem

my sql below is use for listing stock added from 10 days ago. Order by isnull(Price) is use so that stock without any price yet will still being listed. AddDate and Price has an index. SELECT Id, ...
0
votes
2answers
714 views

Run query faster, what index to use

I have a table with 85M rows : CREATE TABLE emissions_totales ( "schema_source" varchar(150), "snap" varchar(20), "gid" varchar(255), "polluant" varchar(50), "emi" float8, "numreg" varchar(3), ...
7
votes
1answer
1k views

How to set SQL Server index pages per fragment?

I have SQL Server 2008, and a number of databases. I have discovered that one of my table's indexes is extremely fragmented (How I know: http://msdn.microsoft.com/en-us/library/ms189858.aspx) The ...
0
votes
0answers
180 views

How implement MySQL unique index with two foreign key that one can be null?

I would know if can be declared in MySQl to create an index constraints in a table with two foreign key that one can be null. For example cannot be repeated a null foreign key with the other foreign ...
0
votes
1answer
408 views

Is index on foreign key used? (No difference in EXPLAIN.)

Essentially, I am joining two MyISAM tables and have found that the EXPLAIN output for the query does not change regardless of whether I have an index on the foreign key in the parent table. I'm not ...
1
vote
0answers
79 views

Oracle - Mysterious indexes

I have a table in Oracle 10.2g that I'm trying to import roughly 11 million rows into. The table contains an SDO_GEOMETRY column. It previously had NOT NULL constraints on all 3 columns, a primary key ...
0
votes
1answer
106 views

Will Partitions and Indexes on the same table help in performace of Inserts and Selects?

I have a table containing the list of visitors and this table has the following information. Visitor Browser Information Visitor Location Information Visitor Time Information No of Visits I have a ...
6
votes
2answers
8k views

How to design indexes for columns with NULL values in MySQL?

I have a database with 40 million entries and want to run queries with the following WHERE clause ... WHERE `POP1` IS NOT NULL && `VT`='ABC' && (`SOURCE`='HOME') && ...
2
votes
1answer
564 views

Longest prefix search in Oracle

I have a list of phone number prefixes defined for large number of zones (in query defined by gvcode and cgi). I need to efficiently find a longest prefix that matches given number PHONE_NR. I use ...
6
votes
2answers
253 views

Does an index with multiple columns make a similar index redundant?

Let's say I have a table that looks like this: CREATE TABLE Activity ( ActivityID int primary key identity(1,1) , ActivityName nvarchar(10), InactiveFlag bit ) with an index that looks ...
3
votes
0answers
198 views

custom population of full text index

Is there any way to populate a full text search index without storing the backing information in the database? I don't mean using remote-blob-storage or FILESTREAM types. The backing information is a ...
7
votes
3answers
3k views

Dropping Hypothetical Indexes

In the past I thought I'd deleted hypothetical indexes using either a DROP INDEX statement for clustered indexes and DROP STATISTICS statement for non-clustered indexes. I have a database that is ...
5
votes
2answers
790 views

Should I use a composite or single-column index?

I have the following columns in my database table (Medicines). ID bigint, MedicineName nvarchar(50), BrandName nvarchar(50), MedicineCode nvarchar(20), and price,quantity. I am making a stored ...
36
votes
4answers
27k views

Index Seek vs Index Scan

Looking at an execution plan of a slow running query and I noticed that some of the nodes are index seek and some of them are index scan. What is the difference between and index seek and an index ...
2
votes
0answers
57 views

How to make continues cluster?

I have a report table with the following index: providerid, date The table is around 30M records and it grows about 100K rows per day. I want to use in the index above as a cluster, but as I ...
0
votes
1answer
106 views

Can I use the database and query it while full-text indexing?

I need to index my database, but I need to query it while it is indexing, it may take a long time, can I do that?
3
votes
2answers
6k views

SQL Server clustered index high fragmentation

I've got a Table with an Integer (4bytes) as primary key. it's defined as an identity. it is also the clustered index. Inserts are working perfectly fine. After inserting 2000 rows the fragmentation ...
0
votes
1answer
134 views

Two identical MySQL tables, one not using indexes

I have one MySQL Server (5.0.37) on a Linux Server that have many databases. Some of them (12) have each an identical table to log sensors data. Schema of one table CREATE TABLE `measuresHistory` ( ...
7
votes
1answer
5k views

MySQL Hanging Completely when `ALTER TABLE… ENABLE KEYS`

I know very little about database administration but I have to deal with some very large tables on my site. This server has 64GB of RAM and Intel Core i7-3820 (4 x 3600 MHz). Most of everything it ...
4
votes
1answer
90 views

How can I get this query to use it's index?

Queries matching this query below shows up in the slow log (with different contentVersionId & modifiedDateTime). As I don't really know what I'm doing I tried adding indexes to all columns in ...
8
votes
1answer
5k views

Why disabling a clustered index makes the table inaccessible?

When an index is disabled, the definition remains in the system catalog but is no longer used. SQL Server does not maintain the index (as data in the table changes), and the index cannot be used to ...
0
votes
1answer
67 views

Index on a query with order

I have the following table with >1M rows: CREATE TABLE `wishlist_place` ( `id` int(11) NOT NULL AUTO_INCREMENT, `wishlist_id` int(11) DEFAULT NULL, `place_id` int(11) DEFAULT NULL, `city_id` ...
1
vote
1answer
2k views

Varchar index - will hashing value make it faster?

I have a VARCHAR(1000) column in a table. It will contain strings that will not be guaranteed to be unique. I have a query that searches this column as part of a WHERE IN clause, the list of values in ...
1
vote
2answers
4k views

Auto-generate scripts to create tables, indexes, etc

In SSMS, we can right click a database/table/index/... and select the "Script As" option to generate a drop and create script. Is there a way to automate this script generation and drop the scripts ...
0
votes
2answers
583 views

Sync Indexes between two tables

I need to automate and Sync only indexes between two tables ( Primary and Stage_Table) within the same database. I tried using SSIS SQL Server Objects Task, but looks like it works only when we sync ...
4
votes
1answer
678 views

Indexes file damaged, was on ramdisk

I have put some of my indexes into a filegroup that contains one file, that file is on the ramdisk, the performance is great, but the problem is that the file was deleted incorrectly (the file ...
5
votes
1answer
9k views

Why does CREATE INDEX … WITH ONLINE=ON block access to the table over a period of minutes?

I have an existing table: CREATE TABLE dbo.ProofDetails ( ProofDetailsID int NOT NULL CONSTRAINT PK_ProofDetails PRIMARY KEY CLUSTERED IDENTITY(1,1), ProofID int NULL, ...
2
votes
1answer
786 views

Rebuilding Unique Index with uniqueidentifier in SQL Azure never succeeds

We have a number of tables (~1M records) that have a column on them defined as: [GlobalID] [uniqueidentifier] NOT NULL that gets auto-populated with newid(). We use this ID for synchronizing data ...
1
vote
2answers
5k views

How do you correct a corrupted index in Oracle?

I have this ORA error in our logs: Caused by: java.sql.BatchUpdateException: ORA-01578: ORACLE data block corrupted (file # 8, block # 22921) ORA-01110: data file 8: ...
0
votes
1answer
354 views

How do you correct a corrupted index in Oracle? [duplicate]

I have this ORA error in our logs: Caused by: java.sql.BatchUpdateException: ORA-01578: ORACLE data block corrupted (file # 8, block # 22921) ORA-01110: data file 8: ...
1
vote
2answers
2k views

Why PostreSQL 9.2 does not use index scan if it can?

My PosgreSQL planner (9.2) does not pick index and rather choose to do seq scan. Here is my table. The index I am talking about is name_left_prefix cwu=# \d web_city; ...
1
vote
2answers
416 views

Is there slowdown inserting into an InnoDB table that has no index set?

I have an old application with lots of InnoDB tables, that have no indexes at all, not even a primary ID or such. Those tables only contain a few thousand rows. Would it be faster to INSERT data ...
1
vote
0answers
43 views

parenthetic grouping of join clauses

What is the difference between these joins? a left join b left join c (a left join b) left join c a left join (b left join c) Does the grouping only affect the order of the joins? Will the query ...
1
vote
2answers
439 views

Clustered vs Nonclustered Index

My database currently has a primary Key/Clustered index on the ID column for each table. However, the application that connects to the database is always looking at views defined as: SELECT * FROM ...
3
votes
1answer
543 views

mysql: need help to optimize my query/table

I'm wondering if someone could help me optimize my tables/query to speed up a query. It is currently running ridiculously slow. I think a well-thought out index could help me. Any help would be really ...
3
votes
2answers
428 views

Reducing Log Impact During Re-Indexing

We use Ola's maintenance solution and its great. Regardless of method for re-indexing a major friction point with IT is the amount of log generated during the weekly re-indexing process. For a 1TB ...