A class of issues where a database executes a query inefficiently due to the optimiser selecting an innapropriate query plan.

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Identical Postgres index scan taking 5x longer on server

I have an intermediate table for managing a many-to-many relation between tables called Expert and Subject: Column | Type | Modifiers ...
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230 views

SQL nested select (query rows after variable), running slow

Have large table (Sybase) rows = 6276225. I'm pulling call status and my query is very slow. In effect what I’m trying to do is pull data for any event after my variable. While querying for just one ...
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92 views

Performance Optimising MySQL query

I have this query in my mysql database, when i execute this, it takes about 4 sec. To give me the result (on xampp 1.8.0 with mysql 5.5) I was wondering if there is any way to enhance this query so ...
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1answer
76 views

Long running query

This is my long running query: select * from t_keyword where id in ( select rel.element_id from t_event event join t_event_element_rel rel on event.id = rel.event_id where ...
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2answers
153 views

How can I optimize this query and support multiple SKUs?

My current query only can select one SKU at a time. I can leave salesite_id constant. If there is a way to also have varying salesite_ids that would be good too, but not necessary. Also any ...
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133 views

How to load XML data into an oracle db table ?

Is there a way to load the XML format data into an Oracle 11g DB table directly ? I mean, Can we write a Stored Procedure to accomplish the same in a more efficient way with the best performance ? ...
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41 views

Resource to learn writing most efficient and highly optimized sql queries [duplicate]

Possible Duplicate: Learning to Optimize SQL Queries and Understand Execution Plans - Resources? Can some one point me to a great book/great books or some really solid reference/references ...
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1answer
178 views

Normalization and Breaking down tables for InnoDB

I'm designing a web application, something small but deals with lots of read and inserts. Let's say 60% read and 40% writes. My storage engine is InnoDB on MySQL. I have a table called User which has ...
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1answer
126 views

How index work in oracle? [duplicate]

I want to understand : How index work in oracle. How they are stored in the disk. How they increase the efficiency of a query? By third point I means how Index contribute to the efficiency of ...
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1answer
70 views

Is it possible to optimize this query? Or any recommendations to speed it up?

After looking at my mysql slow log file I see that almost every entry there is related to this query: SELECT n.nid AS nid, AVG(v.value) AS rating FROM node n LEFT OUTER JOIN votingapi_vote ...
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1answer
125 views

How to optimize indexes on MySQL query with various sorts

I have an INNODB table levels: +--------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | ...
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1answer
314 views

optimize big sql query

My query has to return a statistics for example for march containing productname and price and its sidedishes (1:n relation) with the right price of each sidedish and the right tax for each sidedish ...
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1answer
104 views

Query performance in SQL Server [closed]

What factors should I check when I compare the performance of a query? I saw many articles stating about IO cost, subtree cost (by using Execution plans), statistics such as CPU time, elapsed time ...
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2answers
905 views

Query to search for a substring in xml

I use below query to search for a substring in whole xml(including node name and node value) SELECT * FROM tablename WHERE ( Charindex('abc',CAST([xmlcolumn] AS VARCHAR(MAX)))>0 ) I want an ...
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4answers
115 views

Dropping and recreating indexes [closed]

I most often come in a situation where the users move there database from one server to another and immediately after they move they face performance problems(slowness). I somehow manage to rebuild ...
-1
votes
1answer
42 views

Approximate MySQL Query Time For A Where Clause On A 10 Million Records Table

I'm looking forward to designing a database (in MySQL) but before I start I need to have some calculations to make sure that my application will remain efficient even if there are 10 Million+ rows ...
-1
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1answer
22 views

How can I optimize a big query when EXPLAIN hints don't work?

We have an application that uses MySQL Ver 14.14 Distrib 5.5.35, for debian-linux-gnu (x86_64) using readline 6.2, which esentially manages lots of data from lots of people over lots of tables and ...
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votes
1answer
70 views

Maximum dataset size for a well-performing SQL Server 2012? [closed]

We're planning a project using SQL Server 2012 for storing about a billion records over less than 50 fields. Assuming good hardware, is SQL Server up to that task? Roughly how many request/second can ...
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1answer
80 views

How big the database should be in order to take 30 minutes to query

We have few tables each containing 2,5 million rows in average. Then there is a select query with joins. It takes more than 30 minutes to execute. The db server runs on a machine with 9GBs of RAM and ...
-2
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1answer
236 views

Second time query execution using different constants makes faster? [closed]

Can someone explain or direct me how execution on indexes happen with different constants at intervals in Mysql. I notice only for the first execution on the table it takes time, after that with ...
-2
votes
1answer
542 views

what's the fastest method to export a table through sql query ? 11g - performance

I'm connected to the oracle server remotely. I need to export a table data(the whole table) with millions of records but due the hosting restrictions I can only use SQL (no exp , expdp) . Therefore ...
-3
votes
1answer
539 views

Single query to copy data from 3 tables into a single empty table

In an interview today, I was asked if I could write a single query to copy data from 3 source tables to an empty destination table. I started saying "I will use a temp table or table variables", ...
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votes
2answers
493 views

Optimisation sub query SQL Server

I would like to optimise the query below because it's actually taking 40% of the time in the real one. I HAVE to get the first line in the table 2 for each line in the table 1. The relationship is 1 ...
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2answers
66 views

Performance with IN clause

Does indexed data affect query performance? means If I passed value as 1,2,3,4... in ordered form in any IN clause, can it improve query performance? and what happen in case I pass value randomly ...