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

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2answers
886 views

Why does my query run faster after I force full table scan?

I have a MERGE statement that took forever to execute the select as the table it is running from (SUB_DATA) is rather big (read 1.4 Tb, 700 million rows). My SELECT looks like this. SELECT ...
2
votes
1answer
161 views

Need some help with this query get all status and their associated comments of me and all my friends

I've several days dealing with this query but can't get it to works as I want. This post is related to this one Several values from different tables in which I tough found the solution but I was ...
2
votes
3answers
2k views

Is it normal to use many Triggers?

I have many so-called summary columns throughout my database to count number of rows in other tables. For example, counting the number of comments by a user (a column in the user table). Currently, I ...
2
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2answers
40 views

Is it a better idea (performance is key) to store in a normalized table and retrieve by JOIN or in a single nvarchar column and retrieve using LIKE?

NOTE: The application is not really about websites or keywords, I am using that here only to provide reference points for discussion. I have a data set that is really just a string of words. Think of ...
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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 ...
2
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1answer
2k views

Query taking non-consistent time to execute [closed]

I have a query which takes large time to execute sometimes.When i checked the speed it was taking 15 seconds.But actually it should run faster than that.When i again checked the query it again ...
2
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2answers
152 views

Different queries result in big difference in performance

I have 2 similar functions, different way result in big diff in performance. The PostgreSQL version: 9.2.1. Function 1 create or replace function func_1() returns text as $$ declare v_i ...
2
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2answers
1k views

Slow MySQL query with Order and Group by

I have a query that is taking a long time to execute (1.13s). The two tables user_articles and articles have around 25,000 records. This is the query: SELECT `user_articles`.* FROM `user_articles` ...
2
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1answer
109 views

Slow Query Gets Even Slower After Indexing

I have a MySQL database with just one table containing 8 million records. I need to query the table to find a single record that matches a specific number: select * from my_table where ...
2
votes
1answer
1k views

how to improve query performance

## Only 1 query which returns 10 rows. ## It took about 66 secs mysql> explain SELECT al.log_id , al.user_id , al.page_name , al.section_name , al.submit_time , al.url , ...
2
votes
1answer
137 views

How to know what to investigate and how for a VERY slow stored procedure

I have inherited a large and slow stored procedure and it's giving me a nightmare: I'm not a DBA, although I have some knowledge, but I don't know where to start to identify this bottleneck. I have ...
2
votes
3answers
278 views

How to get all non deleted messages from one user

I have two tables one for messages called default_messages and the other for recipients called default_recipient. This is how SQL for those table looks like: CREATE TABLE IF NOT EXISTS ...
2
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2answers
1k views

How expensive are SELECT FROM LIKE statements from a design perspective?

I have a situation running out of control regarding an ever increasing number of small static files I need to access randomly in a large directory structure. I MUST reduce the number of those files ...
2
votes
1answer
376 views

Oracle ash report

Recently, i have been handed over with an ash report from DBA. To me this report is like french. I have no idea what it is about and what all is written in this report. Can someone please guide me in ...
2
votes
1answer
74 views

How to speed up select distinct?

I have a simple select distinct on some time series data: SELECT DISTINCT user_id FROM events WHERE project_id = 6 AND time > '2015-01-11 8:00:00' AND time < '2015-02-10 8:00:00'; And it ...
2
votes
3answers
92 views

Change table scan in query plan to seek

I have an ORM generated query (Django) running against a local Postgres 9.1.11 instance that looks up ~5 records from two specific match fields. Due to the nature of the EDI load program, I need to ...
2
votes
2answers
9k views

Why can't we access SQL Server when a long query is running in Management Studio?

We have a SQL Server Database (2012 Standard edition). The database is accessed through an ASP.Net web page which displays the count of databases in different tables on page load. This work fine ...
2
votes
1answer
233 views

How to optimise window queries in postgres

I have the following table with approximately 175k records: Column | Type | Modifiers ...
2
votes
1answer
220 views

Postgres Performance Over Group by with MAX and MIN

I just want to retrieve the data for specific location of customers with their ever first and last purchases made in the system. Table details : CREATE TABLE customer_location ( id UUID, location_id ...
2
votes
1answer
175 views

Select data based on records created_at column

I have two tables Keywords, ProjectReports: http://sqlfiddle.com/#!15/06ae3/1 As you can see in that example everything works fine, but I want to get more data from those 2 tables and I don't know ...
2
votes
1answer
688 views

How to get query runtime in PL/pgSQL to be as fast as console query runtime?

Basically I want to assign the result of a query to a custom type attribute. However I noticed that querying directly from the PostgreSQL console was about 0.071 ms and inside the function was 0.400 ...
2
votes
1answer
280 views

Why would a query in code be slower than a query in a SQL tool

When we face performance issues with out application, one of the first things we do is try to isolate if the problem is the code, the queries or the database itself. The most frustrating part of this ...
2
votes
2answers
1k views

Is there a difference in performance between @date and getdate()?

Usually I use the getdate() function in my where clauses to go back in time. Something like: DOC.DATUM >= DATEADD(DD,-1*SSN_SDO.DANA_ZA_POVRAT,GETDATE()) Will SQL Server 2008R2 perform faster ...
2
votes
3answers
2k views

MySQL: can not get rid of “Using filesort” in a simple query

Simple query but can not get rid of "using filesort": CREATE TABLE IF NOT EXISTS `online` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `uid` int(11) NOT NULL, `expiration` int(11) NOT NULL, ...
2
votes
1answer
332 views

Parameter triggers different execution plan, but why?

I have a table CREATE TABLE [dbo].[Numbers] ( [Date] [date] NULL, [Time] [time](3) NULL, [Value] [char](10) NULL ) and the table has > 10 Billion rows, therefore it ...
2
votes
1answer
1k views

How to speed up mysql query?

I have query : SELECT `school`.`ARCO_name`, `student-`.`ClassSize_7`, `student-`.`ClassSize_8`, `degree_o`.`degree_code`, `accredit`.`full_faculty_3`, ...
2
votes
1answer
38 views

Why can't I view the plan for view creation…?

mysql> EXPLAIN EXTENDED create algorithm =temptable view fisgen_temptable(inter,phone) as select intercom1,phone from fisgen where fid='f105'; I am getting an error like this: ERROR ...
2
votes
1answer
48 views

How can I speed up an sql query that round trips between two tables

I first posted this question on stackoverflow, and now I see this site, seems more relevant. These tables are not that big, but the time taken to process this query is long. What can I do with the ...
2
votes
2answers
648 views

SQL Server - Logical Reads lowered, Execution time remained the same

A view executed Select columns from view where col= "date range" (view contains calculation in it Col1+Col2*col3 AS Col4). It took 7 seconds for 500K rows to return, logical reads some 144k. Added ...
2
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1answer
1k views

MySQL: Which join is better between left outer join and inner join

Which join is better peforming if all of them provides the same result? For example, I have a two tables employees(emp_id,name, address, designation, age, sex) and work_log(emp_id,date,hours_wored). ...
2
votes
2answers
653 views

Super simple mysql query taking too long

I have the following: SELECT * FROM autorepair WHERE zip_code IN (91316,91356,91416,91426,91436) AND specialty = 'transmission' ORDER BY ABS(91316 - `zip_code`) LIMIT 0,10 Indexes: -zip_code ...
2
votes
1answer
179 views

Query returning unused stored procedures

When I run SP_askbrent@asof = '2014-05-20 16:00' a period where the database was timing out, I'm getting dozens of CREATE PROCEDURE xxx entries. When I run the following query, the results show the ...
2
votes
1answer
44 views

Will composite indexes or unique indexes help with query performance?

I need help with identifying indexes to increase performance of the following query. I'm currently using v5.5 with InnoDB. I cannot modify the query. However, I can add indexes as needed. The ...
2
votes
1answer
43 views

General purpose view for last value in a group

I am trying to create a view to show the last value in the group. Looking for a more general purpose query. CREATE TABLE a ( id INTEGER, seq INTEGER, val VARCHAR2(16), PRIMARY ...
2
votes
1answer
568 views

MySQL: What is the most optimized way to use datetime type field in query

I am working on optimization of some slow queries in my application. I found a query in which datetime comparison has been used. Below is the subquery: select * from jos_content c where c.visible = 1 ...
2
votes
2answers
123 views

Convert to Self JOIN

I have a correlated sub query, which is taking 16 Minutes to execute. How can I convert it to join or optimize it. SELECT SSF.SM_StockCode, SSF.ST_ItemSize FROM Stock AS SSF WHERE ...
2
votes
2answers
336 views

Trigger update does not seem to finish

I'm new to PostgreSQL triggers & functions and such. I've got a table: keywords and each keyword should be unique. So when I try to insert a keyword that already exists, it should simply update ...
2
votes
1answer
1k 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 ...
2
votes
1answer
137 views

Are there differences in performance of getting data between FullText Search and indexed columns

In SQL Server 2008 R2 I have a query which looks like create stored procedure give_me_art @filter varchar(15),@skl_id int begin select id,naziv,sifra,isnull(lager.kolicina,0) as lager from art ...
2
votes
2answers
428 views

Efficient way to query set of rows from MySQL

I am using MySQL database engine. My Java application uses simple JDBC to retrieve data from database. I have following database schema: main table with two columns: (INTEGER id, BLOB data). id is ...
2
votes
2answers
3k views

How do I force a JOIN to use a specific index in MySQL?

I have a query that JOINs 2 tables; lineitem and part, select sum(l_extendedprice* (1 - l_discount)) as revenue from lineitem force index for join (l_pk), part where ( ...
2
votes
1answer
614 views

inner join on PK with extra criteria slow despite indices?

Given the two tables below I am struggling to understand: why is the third query slow even though first two queries are fast what exactly is EXPLAIN saying can I do anything to significantly speed ...
2
votes
1answer
141 views

Combining columns in index

With reference to RolandoMySQLDBA's answer on MySQL: Index when joining to tables not being used (Performance optimizing question) He mentioned Make sure you build an index that involves the ...
2
votes
1answer
103 views

Optimising query on view that merges similar tables with a clear discriminator

Using PostgreSQL 8.4, I have a number of tables that have a very similar structure, but that belong to different categories: CREATE TABLE table_a ( id SERIAL PRIMARY KEY, event_time TIMESTAMP ...
2
votes
1answer
539 views

Should I use left join to do my job in this scenario?

What I want to do is to find out the items which appeared more than once in this table: mysql> desc tables; +-----------------+---------------------+------+-----+---------+-------+ | Field ...
2
votes
2answers
127 views

CPU or Page Reads

While comparing query performance should i go for CPU values or Page Reads. On live server (with better hardware) a query is showing different CPU when i test it on my local machine. But Page Reads ...
2
votes
1answer
2k views

postgres composite index design

In my rails application using the Postgres database, I have a table called tw_schedules which belongs to a scenarios table (one scenario to many tw_schedules). In addition to the scenario_id foreign ...
2
votes
1answer
1k views

How to optimise read/write performance a MySQL table with many rows?

I am developing a django application where I use a MySQL database. In my application there is one table for domains information which has only 2 coloumns id domain_name but I have a problem when I ...
2
votes
1answer
260 views

Query tuning - SQL Server

One of our developers are trying to run the below query on a development server, which involves pulling data from a linked server, production. The query ran for more than 14 hours before it was ...
2
votes
1answer
155 views

MySQL optimization question — how to speed up a simple query

I have a very simple database, one table with five columns (one INTEGER key, two VARCHAR, a DATE, and a DOUBLE). The table contains 909,000 records. A simple query like SELECT t.price FROM ...