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

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1answer
369 views

Speeding up MySQL NOT IN (Subquery) [duplicate]

I'm currently up to try to improve the performance of some of my queries. As far as I know, statements like "IN" or "NOT IN" are even faster with a large amount of values if a subquery on an indexed ...
0
votes
2answers
88 views

Help creating this query

I'd like to integrate the following query: SELECT parent.id , COUNT(child.id) AS child_count FROM messages parent INNER JOIN messages child ON child.parent_id = parent.id ...
0
votes
1answer
172 views

Is it possible to avoid filesort?

Is it possible to avoid 'Using temporary' and 'Using filesort' for the following SELECT query? I can't figure out a way to do it. I tried adding indexes, for both top_expire and program, but didn't ...
0
votes
0answers
53 views

Faster way to GROUP or ORDER dynamic fields?

We have this query in our app, that searches a table for a song title using MATCH AGAINST and picks the most relevant results. The table has around a million results and is growing. The app has been ...
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0answers
15 views

Get turno.tipo, maquina.patente and operador.nombre and status, complex query

I've this DB design I'm trying to build a query where I should get turno.tipo, maquina.patente, operador.nombre and detalle_emisores.revisado` but it's a bit complex to my knowledge. I started this: ...
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0answers
287 views

Properly index magento mysql tables to improve specific query performance

I am running magento community edition and its db performance is horrible. I have the following query: SELECT `width_idx`.`value`, COUNT(DISTINCT width_idx.entity_id) AS `count` FROM ...
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0answers
83 views

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 ...
0
votes
0answers
232 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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0answers
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 ...
0
votes
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 ...
0
votes
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 ...
0
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0answers
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 ? ...
0
votes
0answers
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 ...
0
votes
1answer
182 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 ...
0
votes
1answer
150 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 ...
0
votes
1answer
72 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 ...
0
votes
1answer
126 views

How to optimize indexes on MySQL query with various sorts

I have an INNODB table levels: +--------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | ...
0
votes
1answer
322 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 ...
-1
votes
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 ...
-1
votes
2answers
946 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 ...
-1
votes
4answers
117 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
43 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
votes
0answers
42 views

Sort warning tempDB spill

I am getting a sort warning tempDB spill with one of my queries, I cant for the life of me figure out how to stop it. I have the following indexes on this table (among many others): (title_nm, ...
-2
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 ...
-2
votes
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
votes
1answer
237 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
555 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
549 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", ...
-3
votes
2answers
496 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 ...
-4
votes
2answers
67 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 ...