In the context of a database, optimisation refers to the process of the query optimiser selecting an efficient physical execution plan.

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Querying number of tries since last successful log, checking IP as well as user

I asked this question before on stackoverflow, but it might fit better here, since it is mainly about database performance. The actual question With performance in mind, how would you go about ...
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Building A SQL table horizontally VS vertically

What is a better design principle when designing SQL Server tables. One can either add columns (ie grow horizontally) or grow it vertically (ie rather adding rows) I have a situation when there are ...
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1answer
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inserting large quantity of data into mysql table

I need to insert about 400 000 000 rows of test data into the InnoDB table. Table is quite simple: CREATE TABLE IF NOT EXISTS `tgt` ( `id_1` int(10) unsigned NOT NULL, `id_2` int(10) unsigned NOT ...
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Significant difference between duration for querys in SHOW PROFILE and SHOW PROFILES?

I have use mysql profiler to optimize an opencart query which takes more than 10 seconds to executes. mysql> SHOW PROFILES; +----------+-------------+-----------------------------------------------...
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1answer
453 views

How do I 'hint' the cardinality of a recursive CTE?

I'm using the following recursive CTE as a minimal example, but in general, the optimizer has to use default 'guessed' cardinalities for recursive CTEs: with recursive w(n) as ( select 1 union all ...
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MySQL queries are 10 to 100 times slower after OS reboot

I have a MySQL server running on Ubuntu. If I restart the MySQL, everything is fine. If I however restart the OS, my queries take anywhere from 10 times to 100 times as long. The only "solution" to ...
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1answer
1k views

Optimizing GROUP BY Query

I'm running the following query: SELECT `type`, MAX(`time`) AS `last_updated` FROM `stocks` GROUP BY `type` On the following table: CREATE TABLE `stocks` ( `id` int(11) NOT NULL AUTO_INCREMENT, ...
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1answer
256 views

Why does the CBO not chose a lower cost skip scan without stats?

In the script below, the CBO chooses an INDEX FAST FULL SCAN over an INDEX SKIP SCAN (this is illustrated by the queries with the UNION ALL but you can demonstrate it is true with just explain plan ...
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1answer
741 views

How to improve the performance of SELECT queries with multiple JOINs on a 50GB database hosted on AWS m3.medium MySQL RDS?

Example query: SELECT p.ListAgentEmail, p.ListAgentFirstName, p.ListAgentLastName, p.ListingKey FROM Property_RES AS p INNER JOIN Property_RES_COUNTIES_OR_REGIONS ON ...
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Modification to GEQO (Genetic Query Optimization) of PostgreSQL

I need to implement a functionality that is in line with the GEQO functionality of PostgreSQL. I understand that GEQO approach is to encode query plans as integer strings and GEQO generates these ...
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1answer
499 views

Optimize where clause using dates

I'm trying to optimize several queries that all use a similar pattern on one of the WHERE clauses: AND (DATEADD(DAY , ISNULL(a.[due_days], 30) + 30 , [dbo].[CalcDate]([type], ...
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2answers
907 views

How to improve row estimate of 1 row in join for newly inserted data

A custom statistic exists for the CacheId column of a table. After an overnight statistics update: Statistics for INDEX 'ST_TableName_CacheId'. -------------------------------------------------------...
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3answers
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Is there any command to optimize all MySQL tables one by one automatically?

I execute below command line statement to optimize a table: optimize table tablename; Is there any command or statement which can optimize all the tables one by one of the selected database?
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1answer
93 views

How to prepare executon plan for given sql query on a server with 4 processors (Oracle database)

4 processors means the query runs in parallel. Select /*+ parallel(4) */ T1.A FROM T1,T2,T3 WHERE T1.A = T2.A AND T1.B=T3.B AND T1.C=T3.C Tables T1,T2 and T3 have 4,8, and 16 partitions ...
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1answer
594 views

New query slower even if it has less logical reads than the old one

I have a query in a stored procedure that must list all dates in a range and JOIN on it date from a table, if it exists for that day. The procedure was created before I was employed as the DBA, so I ...
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1answer
281 views

How to store temp tables in memory during table “optimize”?

When optimizing tables, SHOW PROCESSLIST lists it as "copying to tmp table". I'm trying to ensure the copy takes place in memory to speed up the process. I've tried adjusting the tmp_table_size to ...
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1answer
238 views

sql indexing and performance

I am using mysql5.1, i have table which has about 15 lakh (1.5 million) records.This table has records for different entities i.e child records for all master entities. There are 8 columns in this ...
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1answer
239 views

How can I apply heuristics to optimise an expression tree?

I've converted the following SQL query: SELECT name FROM dog d, works_at w WHERE (d.owner_name = w.person_name) AND (w.kennal_name = "Breeders"); into the following expression tree: My main ...
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1answer
327 views

Clustered composite key high fragmentation and fill factor

I've recently made a table to hold the language preferences of my users as follow: CREATE TABLE [dbo].[systemUserLangPreference]( [systemUserID] [int] NOT NULL, [langID] [int] NOT NULL, [...
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2answers
370 views

What's the best way to translate a website [closed]

I have a website in Django using MySQL, and I have more than 4.000 entries that I want to translate. What's the best way to do it? Create a new database for every language? Create other table for ...
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91 views

explain plan ,joins and optimization

I have to join 6 tables in sql query and each of these tables have 1 join to each of there master tables . Hence i have defined 5 subqueries within a sql query but i am seeing a lot of performance ...
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1answer
471 views

Why query optimizer doesn't use negative filter index

I have a table that has following structure, as you can see, there are one clustered index and two non-clustered indexes, one non-clustered index is IX_ParentId_Include, and another one is ...
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2answers
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Should I include as much information as possbile to help the optimiser?

Reading the article "Dynamic Search Conditions in T‑SQL" I saw the following statement in the "Using sp_executesql" section. Double Feature You may wonder why there are two conditions on the ...
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2answers
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Optimize query with indexes

The following query is looking for all towns that are between 5 and 10 kilometers from a hard-coded latitude/logitude (=another town actually). I have 37010 towns. I'm using Symfony 2 which "creates" ...
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1answer
247 views

Most efficent DELETE Method

I must choose between three possible DELETE methods in SQL Server. The table: RawData stays at around 500GB. Here is the table: CREATE TABLE dbo.rawData ( rowId INT IDENTITY PRIMARY KEY, ...
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1answer
137 views

Logical optimization of joins and selections

I am studying query optimization. I have read that it might be preferred to apply relational selections before a logical join operation. Is there a scenario where joining first and then applying ...
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1answer
2k views

How can I speed up a Postgres query containing lots of Joins with an ILIKE condition

I have an odd problem which I really don't understand. Simply put I have a join containing 4 table joins, which I believe all have appropriate indexes, but which takes a ridiculous amount of time to ...
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1answer
6k views

Truncating Table Partitions Containing Data and Global Indexes

I have to truncate a partition (392,000 records) of a table with 20.000.000 records. At the moment, I'm making a truncate table and rebuilding indexes. But the table has 37 indexes and it takes 20 ...
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1answer
493 views

sql-server optimize query with lots of null checks

I have a query such as: select something from somewhere join stuff on condition join more_stuff on condition where somewhere.sometime is null and somewhere.someone is null and stuff.whatever is null ...
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2answers
720 views

Inserting to table: Insert rows with Left Outer Join or Insert rows then Update?

I have a table of Orders and another table of Deliveries. The Orders table will contain a reference to the Deliveries table if there is a corresponding row. Not every row in Orders will have a row in ...
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1answer
120 views

How to index WHERE (start_date >= '2013-12-15')

I have a table named items, and inside the table there is a some_date column, with date as the datatype. I was wondering how can I index the some_date column with PostgreSQL SELECT "items".* FROM "...
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201 views

How can I get rid of the “No Join Predicate” warning

I have this fairly straight-forward snippet of a query: DECLARE @ClientGUID numeric(16) = 9000011916900200; SELECT ch.GUID, c.LastName, c.FirstName, mrn.ClientIDCode AS MRN FROM Client c INNER ...
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MySQL Query Cache - what type of queue is used?

I am wondering what type of queue is MySQL Query Cache using. When there is new query and cache is full which query is deleted? Oldest one? One with fewer number of hits? Or maybe there is some ...
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How to make make my query run fast? [closed]

How to make this query run faster? Table contains over 2 million rows of data and takes around 30 to 120 seconds to process the query. SELECT INET_NTOA(blocks.startIpNum), INET_NTOA(blocks....
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2answers
2k views

Optimized query to fetch a record from 10 million entries

A table has 2 fields | UniqueKey | TimeStamp | ------------------------- | xfsddddq | 1024125412 | | xfstttdx | 1024125413 |< | xfsdxxau | 1024125415 | Estimated, there are 10 million ...
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1answer
726 views

When tables are locked does MySQL queue queries?

I have a small production website, but it's live 24/7. When running the Optimize, Analyze or Repair commands, MySQL locks the table it is working on. QUESTIONS How would this effect users trying ...
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1answer
241 views

MYSQL Stock Database Optimization

I am downloading a bulk of stock data: Ticker symbol, company name, industry sector, Open, high, low, close I was wondering performance-wise if separating the ticker, company name, industry sector ...
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1answer
69 views

Design for hierarchical embedded database

The goal is to construct a hierarchical database of Objects having the following format: TypeA -> ObjectA [values, contains ObjectB*, ObjectC*, etc.] TypeB -> ObjectB [values, contains ObjectC*,...
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70 views

Tagged questions

I have similar to StackExchange network that utilises tagged questions. In my web application Users also can find questions by tags. The query below returns a set of tagged questions: SELECT ...
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51 views

Set default fields

Is there a way to inform the database that some fields are default (have always the same value) so that I don't need include them in all my queries? Suppose: Select ... where f1=a, f2=b, f3=c, f4=d ...
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Opimizing Mysql

Below is a Snapshot of my Server info. And the results of mysqltuner.pl Some help with commands would be appreciated. I'm new to this and have gotten pretty far, but I'm having issue with Mysql ...
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Why is adding a FK constraint slow in MySQL?

I'm doing some experimentation in MySQL 5.1.53 and I've run across a case that I just don't understand. CREATE TABLE A ( `pk` INT(11) NOT NULL, `fk` INT(11) NOT NULL, PRIMARY KEY `pk_A` (`...
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1answer
91 views

Will a specific denormalization increase performance in a specific scenario?

Suppose I have a table with fields | a | b | c | d | ... | z | which contains millions of records and which will serve millions of queries a day. And the field z holds the id of some parameter which ...
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1answer
805 views

Has postgresql a fast add column optimization?

When adding not-null columns with a default value - does Postgresql optimizes this operation? In case the table has n rows, a not-optimized alter-table-add-column would yield n writes of the default ...
2
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1answer
921 views

mysql optimize group by having count

I have 2 mysql table: table t1: CREATE TABLE IF NOT EXISTS `t1` ( `id` bigint(20) NOT NULL, `url` varchar(255) DEFAULT NULL, `title` varchar(255) DEFAULT NULL, `type` varchar(255) DEFAULT ...
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2k views

Indexes for SQL query with WHERE condition and GROUP BY

I am trying to determine which indexes to use for an SQL query with a WHERE condition and a GROUP BY which is currently running very slow. My query: SELECT group_id FROM counter WHERE ts between ...
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MySQL query with order by decreased performance

Here is my schema: CREATE TABLE `UserMst` ( `UserID` mediumint(8) unsigned NOT NULL AUTO_INCREMENT, `EMailID` varchar(50) DEFAULT NULL, `UserName` varchar(20) DEFAULT NULL, `FullName` ...
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2answers
373 views

optimization of expensive subquery

The following query gets the last report (where latitude and longitude and secs are <> 0) associated with the specified units: SELECT reports.* FROM reports INNER JOIN ...
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2answers
165 views

index for OR operator with different columns

What would be best index for this kind of query: -- id is the PK create table test3(id number,name varchar2(30) not null,lastname varchar2(30) not null); select id from test3 where id=:1 and (name=:...