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

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54 views

If a query contains two identical subqueries, will they both run?

Say I have a SELECT query that contains two identical subqueries, like the below: SELECT (SELECT SUM(Price) FROM Product p WHERE p.GroupID = g.GroupID) AS 'TotalCost', (SELECT SUM(Price) ...
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50 views

Slow compilation of a SQL statement

I have SQL Server 2014 and a large table (more than 200Gb) with 100M rows and more than 300 columns. For one "unpivot" query I wanted to see its estimated execution plan and it took more than 90 ...
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1answer
72 views

Tuning Mysql and Monitoring

I would like to know if anybody can point me towards a tool/way for MySQL database tuning ... Actualy the tunning of my.cnf is like below My database is in MyISAM | Mysql 5.1.73 key_buffer = 500M ...
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2answers
282 views

UPDATE query with JOIN taking forever

I'm not very good with databases so please keep in mind even if the solution sounds like something everyone would have already tried, please post it because I likely have not tried it and it would ...
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1answer
50 views

Does it make sense to order condition in where query?

We have a clustered index in table Tbl with order of A,B,C. Does it make senses to write a query to have WHERE A = @a, B = @b, C = @c or it'll be as same as WHERE C = @c, B = @b, A = @a Does the ...
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0answers
73 views

How to handle bad query plan caused by exact equality on range type?

I'm performing an update where I require an exact equality on a tstzrange variable. ~1M rows are modified, and the query takes ~13 minutes. The result of EXPLAIN ANALYZE can be seen here, and the ...
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0answers
58 views

Last few rows from a non-indexed table in Oracle

I'm trying to run a query on an Oracle DB through SQL Server [dont' ask, it's a requirement] The Oracle table in question [lets call it hugeTable] has over 200 million rows and no index. I'm not ...
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55 views

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
37 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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0answers
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
178 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). ...
1
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1answer
190 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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0answers
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
381 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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0answers
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
120 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
311 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, ...
0
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1answer
74 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
184 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
59 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
84 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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0answers
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 ...
1
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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 ...
0
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2answers
50 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 ...
1
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1answer
185 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 ...
3
votes
3answers
187 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
159 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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0answers
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 ...
1
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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 ...
0
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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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0answers
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 ...
4
votes
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] ( ...
6
votes
1answer
216 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
138 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
60 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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0answers
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 ...
1
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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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0answers
57 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
285 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 ...