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

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Mysql query with LIMIT much slower under RDS (5.6) than old 5.1 system

We inherited an old legacy system running on mysql 5.1, and moved it to RDS running 5.6. One query is running much slower - it can take up to 20 minutes to run, where previously it took only a few ...
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1answer
129 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 ...
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17 views

Documents with many potentially overlapping geolocations (maybe MongoDB)

Let's say I have a large list of coordinates coupled with the type of building is at this location (e.g., restaurant, doctor's office). In this scenario, there would potentially be many different ...
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1answer
36 views

How can I time SQL-queries using psql from command line?

I am sorry, I cannot comment, so I am posting a new question. There is already a question "How can I time SQL-queries using psql?" but I am missing answer how to do that from command line. How to run ...
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59 views

Index Tuning Question

I have the following query: SELECT T1.ITEMID, T1.ITEMTYPE, T1.PURCHMODEL, T1.HEIGHT, T1.WIDTH, T1.SALESMODEL, T1.COSTGROUPID, T1.REQGROUPID, T1.EPCMANAGER, ...
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1answer
171 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). ...
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1answer
182 views

PostgreSQL 9.3 - Performance Issue: Counting table entries slower with jdbc postgres driver

I'm using PostgreSQL 9.3 and want to ask if it is possible to improve the performance of my queries based on the following database schema: CREATE TABLE "entities" ( "id" BIGSERIAL, "type" INT ...
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1answer
67 views

Mysql join table order by index

First Master Table CREATE TABLE `edipostingmaster` ( `ID` bigint(20) NOT NULL AUTO_INCREMENT, `applied` int(11) DEFAULT '0', `fileName` varchar(255) DEFAULT NULL, `checkNo` varchar(100) ...
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42 views

How to optimize having bit_or?

Let's start with SQLFiddle http://www.sqlfiddle.com/#!2/64fc5/1 I have some urls and I am making some tasks (crons) related to them. Task can be successful or not. I want to try to do it only three ...
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2answers
380 views

Index seek much slower with OR condition compared with separate SELECTs

Based on these questions and the answers given: SQL 2008 Server - performance loss possibly connected with a very large table Large table with historical data allocates too much of SQL Server 2008 ...
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16 views

Optimization of an old query multiple unioned subqueries

I am currently in the process of optimizing a large query that was written for oracle 8i. My company currently uses oracle 10g which gives us a lot of options for optimization. Please Reference the ...
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2answers
118 views

View with left joins are very slow

I have a view based on join of 3 tables and and query on view is taking 10 mins to fetch the results. Can anybody help me in reducing the time taken to fetch results? VIEW CREATE view ...
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2answers
292 views

Improving `GROUP BY` query performance in sqlite3

I have a little web-application that is using sqlite3 as it's DB (the db is fairly small). Right now, I am generating some content to display using the following query: SELECT dbId, dlState, ...
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1answer
71 views

PostgreSQL - If I run multiple queries concurrently, under what circumstances would I see a speedup? Under what circumstances would I see a slowdown?

I approach you all humbly as one who is NOT a DBA, and I'm sure that my question is fraught with conceptual shortcomings and "it depends on" land mines. I'm also pretty sure that all of you who ...
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4answers
183 views

Are we a good fit for SQL Server Enterprise and table partitioning?

We currently have a production database that contains millions of records (14 million in the largest table). One function of the database is to provide time sheet information so a single table could ...
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3answers
124 views

Why is my select statement so slow?

SELECT name FROM sys.databases WHERE name not in ('master','model','msdb','tempdb','ReportServer','ReportServerTempDB','1303VISBOC') AND CASE WHEN state_desc = 'ONLINE' THEN ...
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1answer
58 views

Last row from a query without Order by

I have something like SELECT var1,var2 FROM table where var3=X AND var4=Y order by var5 desc limit 1; Running this query takes roughly 5 seconds on my database which is far to slow. I was ...
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1answer
83 views

Performance of checking for data in related tables

NB: this question is purely academic / to help improve my understanding of SQL Server performance. Given a master table which relates to one or more other tables, how would you determine the best ...
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58 views

same query different servers,different execution plan and time

I have this query and it runs less than 2 minutes on Test but on Prod it takes 10 minutes. Both are the same version,CPU,RAM,OS the same. I have four tempdb files on Prod but one one Test. I ...
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1answer
47 views

Will Rebuild and Reorganize improve Database Migration Script performance execution?

I would like to know if a Database Schema Migration Script (generated by Visual Studio 2008 or greater) will run faster if my target database got indexes rebuilt and/or reorganized. Note: For all ...
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1answer
49 views

A table that consists of multiple FK or creating separate tables for each FK

I have tables called 'books', 'category', 'subcategory', and 'booksCategory'. Each book can have its own category and subcategories. For example, a Sci-Fi book can belong in the 'category' table under ...
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2answers
49 views

MySQL query performance question

I have a MySQL database where I would like to return results based on multiple rows. id | key | value | selector --------------------------------------------------------- 1 | username ...
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1answer
178 views

Tuning Mongo (TokuMX) for fastest bulk reads

What options do I have for tuning MongoDB / TokuMX for reading the results of queries with large result sets? I'm currently on a single server (no sharding) with the data on an SSD drive. My queries ...
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3answers
186 views

Nested table as condition prevents using index

The following query joining a subquery does a TABLE ACCESS FULL when the master-table uses nested table as condition. When the condition is a simple =, the same query does an INDEX RANGE SCAN as ...
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2answers
154 views

Query Optimization required - Subquery using Inner Join

Could anybody advise how can I optimize this query below please? SELECT IT.[iInternalTransactionID] , IT.[iInternalAccountID] , C.[iContractID] , IT.[dtTransactionDate] AS TransactionDate , ...
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1answer
29 views

How to optimized mysql query having large dataset

I have two tables in MySql with the following schema, CREATE TABLE `open_log` ( `delivery_id` varchar(30) DEFAULT NULL, `email_id` varchar(50) DEFAULT NULL, `email_activity` varchar(30) DEFAULT ...
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63 views

A working view now starts timing out

I have 2 identical databases (one larger, one smaller) with identical views. Recently a view on the smaller DB started timing out. Google searches seems to point to deadlocking of some sorts. If I ...
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1answer
129 views

Why is this second query more expensive than the first?

While reading Graph Databases book, I came across this excerpt: I can't figure out why the second query is more expensive than the first. Indeed, both filter on the Bob person. May anyone ...
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1answer
76 views

A single, simple update takes 10+ seconds

We are running MySQL 5.1.71-log and have a table with 2.7 million rows. Simple updates to it are regularly taking more than 10 seconds to execute. The table structure is: CREATE TABLE `person` ( ...
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39 views

Help with MySQL query which is only occasionally slow? Temp tables/Disc caching?

We have an issue with one particular query whch runs regularly on our MySQL database, though I am not necessarily sure it is a problem with the query itself. 90% of the time it runs perfectly fine ...
0
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1answer
76 views

Help optimizing very slow mySQL query

I have a query which takes about 6 secs to execute. SELECT * FROM (SELECT ord.ID, op.name AS prodName, op.code, ord.date, ord.email, op.total, stat.ID AS statusID, stat.value AS status, ...
4
votes
1answer
179 views

Pull data from multiple tables in a view or function

There are 3 tables from which I need to pull data, and print it in a specific way. http://sqlfiddle.com/#!15/59481/8 You can refer to this question to see how the query was produced. In the fiddle ...
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2answers
128 views

Clustered Table Scan Because of “SELECT *”

I have a Records table with over 100 columns and very many rows, and a nonclustered index on 5 fields based on my access paths: CREATE NONCLUSTERED INDEX [IX_Records_CustomerID] ON [dbo].[Records] ( ...
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1answer
213 views

Sargable Queries

Very simple question I hope, I'm currently having some scripts I inherited into my project reviewed by the database admins. This has never been done before apparently and lots of issues are being ...
2
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1answer
137 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 ...
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0answers
58 views

Performance getting rows with max column

I have an historic table called 'historic', with three columns: object_id, day, value. For historical reason, day(date) is an integer number (number of day since 01/01/1904) Example: object_id | day ...
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37 views

Select changes in table by date

I have following table schema name type id int key string count int date date url_id id with example data id key count date url_id 1 system 100 ...
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1answer
52 views

Mysql super slow

I have a database of movies that I downloaded, it is around 51mb in size. One of the tables has more than 750k records(all separate insert statements(I believe this is bad)). The rest aren't so bad ...
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0answers
51 views

Why is PostgreSQL doing a seq scan on column != column?

Why is PostgreSQL doing a table scan on column != column? Isn't this query guaranteed to return no results? Isn't anything != anything guaranteed to be always false for any record on a not null ...
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56 views

Slow query (Wordpress)

Can I speed up somehow the following query? Somehow to stop from creating a tmp table/filesort. Tried a couple of indexes but no luck. mysql> explain SELECT wp_posts.ID FROM wp_posts LEFT JOIN ...
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0answers
275 views

How to improve query performance in PostgreSQL? [closed]

I have the following query to be execute within a second but getting time for execute 2.8 minutes: Query: Using Common Table Expression. explain analyze with temp_cte as ( Select ...
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0answers
18 views

View in View slower to execute?

Sometimes it's easier and clearer arranged to create a View from another View. Can this cause some speed losses in relation to selecting everything just in one Big and long View-Command?
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0answers
22 views

Optimize finding the next batch of data from A to be crunched and inserted into B

I'm using PostgreSQL to store data produced by a large distributed computation. There are several stages to this computation; the idiom we've settled on is that there's a table containing the results ...
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2answers
1k views

Improve query performance when selecting almost all rows with many “group by” columns

I have a table with 20 columns and about 600,000 records. The maximum row size is only around 100 bytes. The table is repopulated every few days, but the number of records remain about the same. For ...
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2answers
209 views

how to solve slow running sub query TSQL

I have a problem with a slow running query. I have analysed the query with the sql server profiler but I can't seem to find a good solution. I did find why it is running slow. If ask the full ...
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1answer
33 views

What is the generally accepted method and tools for profiling MySQL queries?

Profiling database queries is difficult, and dependent on database technology. In MySQL, what is the usual (or, in deference to that, a great) process for profiling a query? For example: Run the ...
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1answer
101 views

Difference between DATE(time_field) AND time_field in a WHERE clause

I have 3 tables: users movements unique_ids I want to get the records gotten from march until now of the users registered in march, counting the unique id of their movements with a distinct and the ...
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1answer
29 views

selecting rows that have n foreign key conditions satisfied

I'm trying to filter a master table rows based on 2-more conditions from the relative foreign key relation, i came up with this which is working fine, but i just can't convince my self that it's that ...
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2answers
662 views

An efficient way to compare two large data sets in SQL

Currently, I'm comparing two data sets, that contain unique StoreKey/ProductKey combinations. The 1st data set has the unique StoreKey/ProductKey combinations for sales between begin January 2012 and ...
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1answer
162 views

Understanding execution plans using TVPs

I have some slow running queries (8 seconds across 1M records grouped by months) and have been trying to make sense of the execution plans. We use around 10 TVPs to send in a set of filters that the ...