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

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50 views

Oracle Autodop disabled at the table level

I have a question related to Oracle auto DOP and parallel DML concepts. I have a scenario, if I set the Auto DOP set to 1 on the table and if I run parallel DML statements on that table through ...
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1answer
87 views

MySQL: What points should we consider when create composite index

There are multiple views behind the logic of creating composite index in a table. Creating composite index is obvious when we have composite primary key. Beside this, we create composite index on the ...
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2answers
86 views

How should I structure my time based index?

So I have this table in SQL Server 2008. Let's just say it's called TimeSheets. Now, that table has two columns I am concerned with. TimeSheetDate and UserCustomerKey. TimeSheetDate is a ...
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1answer
360 views

What is the Difference between IN and Not IN performance wise?

I am new to database.I am having doubt that what is the difference between IN and NOT IN performance wise. When I am using IN, takes less time for the same query(Logically same query) when I use NOT ...
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2answers
583 views

MYSQL - Why does this SELECT get slower the further down the table?

My table: CREATE TABLE `wp_users` ( `ID` bigint(20) unsigned NOT NULL AUTO_INCREMENT, `user_login` varchar(60) NOT NULL DEFAULT '', `user_pass` varchar(64) NOT NULL DEFAULT '', ...
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1answer
77 views

How can I efficiently search for all records from a given month, or a given year?

We have a couple queries that involve datetime fields. In particular, we are checking for things like SELECT field1, field2, ..., field20 FROM table WHERE MONTH(startDate) == 1 SELECT field1, field2, ...
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2answers
831 views

MySQL: why assign NULL as default value

When we define a table, multiple times we assign default value of a column as NULL. I have How NULL is different than empty value('') as well as 0? Is there any impact of NULL value in query ...
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1answer
199 views

Sequences Vs Count for auto-increment

Can some one please tell me the exact difference between the following statements , INSERT INTO table1 VALUES ((select count(column-name) from table-name2)+1); here i am using the count function to ...
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1answer
81 views

Query a name in large database, optimizations? [closed]

if you would like to query a name in a very large database, are there some ways to optimize this query? If 1 million names are in the database, and the name has to stay as it was registered (and not ...
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1answer
107 views

Index being ignored by Oracle

I have a table for sensor data, simplified it looks like this: DEVICE_ID NUMBER SENSOR_ID NUMBER DATA_TIME NUMBER DATA_VALUE1 NUMBER The table constains billions of rows and is partitioned by week ...
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1answer
423 views

Simple PostgreSQL lookup table is inexplicably slow

I'm trying PostgreSQL 8.4.14 for storing triples, pieces of data of the form (String, String, String). For speed, I'm not repeatedly storing strings but rather using two tables: main table triples ...
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1answer
133 views

Using an enum index to limit records

A common issue, just not sure on the keywords. I have a table of assessments (14k+ records). Each assessment can be in many different states ('draft', 'proofing', 'amends', etc... and 'done'). Most ...
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1answer
394 views

Efficient way to write query for multiple table which depends on column value of a table in mysql?

In the given schema, there is a table A having column A1,A2,A3,A4 There are three more tables i.e. B,C,D If the value in A4 is b, i have to lookup table B. If the value in A4 is c, i have to lookup ...
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1answer
269 views

T-SQL Gurus, I need help optimising these queries for performance

I would like to have suggestions on improving the performance of some queries. These will be run on SQL Server 2008 R2 against a single table called dbo.bids In a production environment the table ...
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1answer
50 views

Query Optimization for added value

I have a query that's behaving a bit oddly. In my database I have a table called "records". It tells me a bunch of information about what applications a user ran on my company's machines. I'm ...
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1answer
58 views

strange “using where” in simple query

I have a table with this structure: mysql> describe user_groups; +----------+----------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | ...
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1answer
33 views

Condense Query Results with Wildcard

I have the following query: select programVersion, count(programVersion) from records R inner join Programs P on P.programID=R.usageProgramID where programName="word" ...
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2answers
1k views

How to use and optimize subquery on 100 million rows

What I'm trying to do is running a job on more than 100 million domains which haven't processed before. I have two tables, "domain" and "domain_setting", on every batch (10.000 domains per batch) I'm ...
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1answer
54 views

Optimizing Query

Can anyone help me tuning this query..... explain extended SELECT DISTINCT a.msisdn FROM `std_msc_opr_wise` a LEFT OUTER JOIN (SELECT msisdn FROM as_treat_pre_usage_30days GROUP BY ...
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1answer
128 views

What is the correct model for related tables with millions of rows?

I need to create a question and answer tables that will have millions (maybe billions) of rows. The current model is: Question Table id_question (PK, auto increment) id_user question_content ...
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1answer
551 views

MySQL stored routine performance while using PREPARE

Instead of maintaining stored routines for each database in my current environment I have decided to create separate database just for stored routines storage. Mainly I am using them for reporting. ...
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1answer
93 views

Speed efficient query for membership first joined, latest category from membership table (min, max)

I have the following table representing membership information: CREATE TABLE IF NOT EXISTS `membership` ( `id` int(11) NOT NULL AUTO_INCREMENT, `organisation_id` int(11) NOT NULL, ...
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1answer
515 views

slow queries - set weight to token type in tsquery - postgresql

Postgresql version 9.2.3! I'm working on a database for mapping of chemical names. My main table contains aprox 91 million records and it's indexed by gin. I want to query it with multiple names (I'm ...
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1answer
73 views

Faster joining on 'most recent' related rows

I have a bug tracking application. The bug table stores very little, because every state change to a bug happens by adding a comment. For example, the current state of a bug is determined by the state ...
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1answer
117 views

Query taking long time

My query is taking around 540 seconds to get result. Please help me to rewrite it. Query: SELECT pd.domain, fd.passkeyid FROM portfolio.domains AS pd, fabulousdomains.domains AS fd WHERE ...
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1answer
294 views

MySQL Partition based on month-year

Is there a way that I can create a month-year partition on the below table? Without having to define all the permuations of month/year combos ? CREATE TABLE visitor_visits ( id int(10) UNSIGNED ...
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1answer
2k views

Is there an easy way to debug and find out why a query runs slow?

I'm running onto a weird issue. We've got two db servers, one is development and the other one is production. Both have same specs. VMs (Hyper-V) Windows Server 2008 R2 64 Bit SQL Server 2008 R2 64 ...
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2answers
290 views

Attempting to avoid SORT in query planner

I have a query that is used VERY frequently in my application. Without modifying the query itself, I'm trying to optimize it by toying with different indexing schemes. Here's the query (basically): ...
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1answer
136 views

Help me to better design my query so I can gain more performance

I need to find so called first entry in database for items regarding their partners. I wrote query and it is giving me correct results but it sucks with performances. I suspect that I have missed ...
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1answer
380 views

Returning Multiple Result-Sets or Single XML Blods

I've been writing some new Stored Procedures, and find myself returning between 6-8 result-sets in a few cases. I've always worked under the assumption that there were certain inefficiencies with ...
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1answer
30 views

Minimizing SELECT latency in PostgreSQL

I am evaluating Postgres 9.4 performance on a machine with Intel i7 quad-core 3.6 GHz CPU, 8 GB ram, and 7400 rpm HDD (no RAID) running Linux Mint. The DB schema has the following table: ...
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70 views

Need your help in query tuning

I read ​one article which shows how to use different aggregations effectively. http://sqlblog.com/blogs/paul_white/archive/2011/12/04/is-distinct-aggregation-still-considered-harmful.aspx I am ...
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45 views

PostgreSQL query taking a long time

I have a query that is taking hours to run. There is a large table to parse, is there any way to optimise this? with VehData as ( SELECT * from dblink('host=databasesrv port=1234 ...
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25 views

Foreign table not using index

I have a table on database temp_db named external_objects and an index on the field id, which is an MongoDB id (like 5458d717cd07870859000003). When I explain this select at this database, I got this ...
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1answer
18 views

database with same schema and same AWS instance type, but different performance

Hi I am getting a new set of production servers ready. I generated a DB script from SSMS using the schema from Server A to deploy to a new AWS instance of the same type as Server A. After populating ...
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1answer
50 views

GROUP BY very slow when returning many rows

I have a query to aggregate data per day. When I run the query for a single day it is very fast. However, when I run the query for multiple days the time cost increases much faster than ...
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0answers
75 views

MySql Innodb Database Slow INSERT Query to Remote Server

I have searched thoroughly on how to improve general performance of my database which is hosted on Hostgator. I have mostly come across performance tuning strategies which are catered to only local or ...
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0answers
36 views

Postgres Query Optimisation (Rails App)

I have a very slow running SQL query that is run from my Rails app using the Model.find_by_sql method. I've made a number of optimisations but it's still extremely slow. It would be great if anyone ...
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0answers
31 views

Create table with select Query on DB link

I'm trying to execute the following query, it is taking more than usual time. I'm retrieving data from db link. Without the create table statement the query is giving results. For Create table also if ...
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1answer
29 views

MySQL 2 Million Rows, longtext and varchar indexes

I'm trying to find a solution for this, with no success. I have a table with ~2M rows, and I need to do a WHERE with 3 expressions using OR. name LIKE '%PARAM%' OR text1 LIKE '%PARAM%' OR text2 LIKE ...
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1answer
37 views

Optimizing a query on Mysql 5.5.24

I am trying to optimize the query SELECT CONCAT(lastname, ', ', title, ' ', firstname) AS fullName, e.lastname, e.firstname, e.email, e.userType, e.userID FROM employee e, ...
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0answers
45 views

Which of sys.dm_exec_query_stats columns should I pay most attention?

I'm trying to tune my database and currently staring into sys.dm_exec_query_stats (with actual queries): SELECT SqlText.text, * from sys.dm_exec_query_stats CROSS APPLY ...
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0answers
9 views

indexing table column on the go of mysql query commit

It is said that to optimize the query cost of execution, then it would be by indexing the field of tables in database. Since I don't have a permission to enter the phpmyadmin in my web server as I am ...
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0answers
25 views

Best way to run a formula (segment) a large number of users with custom attributes

Here is my question. I have a table that stores a large number of people (80 mil). Each person has a GUID id. Then I have another table (or set of tables) that stores information about people. e.g. ...
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1answer
75 views

Improve Query Performance

I have the following sqlite3-Tables: db.execute("""CREATE TABLE IF NOT EXISTS STATIONS (StationUID INTEGER PRIMARY KEY AUTOINCREMENT, StationNumber TEXT NOT NULL, ...
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0answers
126 views

Slow running Oracle query caused by unnecessary full table scan

I'm by no means an expert with Oracle, but I know enough in terms of how to analyze explain plans and perform basic optimizations. However, this time, Oracle has stumped me with it's explain plan. ...
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1answer
39 views

InnoDB Table has backed up INSERT and UPDATE queries, high CPU

I am running an MySQL DB with all InnoDB tables. I often have many queries backed up for the same table when I run SHOW PROCESSLIST; Basically, I keep a table of every logged in customer and update ...
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57 views

How to divide a big SQL Query into small query

I am trying to traverse the whole file system. I am picking each and every file and then trying to insert it into the SQLite Database. Before inserting I am also calculating the checksum of each file. ...
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0answers
99 views

Mysql cursor alternative / Optimization - each row updates are too slow

I'm looking to optimize my cursor based update or actually replacing it... Situation We're carrying out promotional campaigns and I'd like to track user activity per campaign. Logic Each campaign ...
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0answers
43 views

delete query performance issue on mysql

I have two tables table1, table2 where table2 is a subset of table1 (basically created with the query create table table2 as select * from table1 where .....) Now, I am trying to run the below query. ...