Use this tag for questions about improving the performance and/or efficiency of database queries.

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3answers
3k views

Increased query_cache_size, Queries slowed drastically on increased traffic

I increased our servers query_cache_size to 2gb, hoping for performance benefits. After sometime the query performance would drastically decrease. Once I dug in deeper, I found the queries in State "...
8
votes
3answers
11k views

Is it better to separate a big query into multiple smaller queries?

There are situations which require having really big query joining several tables together with sub select statements in them to produce the desired results. My question is, should we consider ...
7
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1answer
179 views

Lead/Lag Implementation in SQL Server 2008 R2: Max memory exceeded

Background I'm trying to establish a "visits" sequence, wherein if an animal is detected at essentially the same place (General_Location) it counts as a single visit, but if it goes elsewhere and ...
6
votes
3answers
2k views

Postgres is performing sequential scan instead of index scan

I have a table with about 10 million rows in it and an index on a date field. When I try and extract the unique values of the indexed field Postgres runs a sequential scan even though the result set ...
5
votes
2answers
1k views

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 ...
4
votes
2answers
518 views

Efficently Remove 90% of a table's data

I am working on a process to remove 90% of a table's data because only 10% is needed for testing. The best way I have found includes storing 10% of the table's rows into a temporary table. Current ...
3
votes
2answers
6k views

Dramatic decrease in SQL Azure performance after scaling to new edition

Yesterday, we scaled one of our databases in Azure from the old Business edition to the new Standard one (S2). Since then, it has been behaving rather erratically. We have a relatively simple table ...
3
votes
1answer
103 views

Do fixed-width rows improve PostgreSQL read performance?

I have a table articles: Table "articles" Column | Type | Modifiers | ...
3
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0answers
895 views

MySQL: Improve performance for one row insert into table with unique constraint

I have a table with ~ 40 mil records, with a unique index on the url collumn, of type varchar(255). Now the insert speed is about 30/s, is this expected? how could I improve it? I can't use bulk ...
2
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1answer
371 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
145 views

join to other table multiplied by loop foreign key in mysql

i have 2 table one node and relation and Second store buy each node. my code work fine but when sum multiple buy for each node result multiplied by number of purchases . table nodes +-------------+--...
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2answers
4k views

How to fix slow LIMIT queries with big offsets without heavily rewriting them?

Imagine a very basic example of your average discussion board. For example: CREATE TABLE threads ( id INT UNSIGNED NOT NULL AUTO_INCREMENT, title VARCHAR(100), PRIMARY KEY (id) ) CREATE ...
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3answers
132 views

MySQL select with between optimization

I got issues with some geo IP query. So basically here is create code of table: CREATE TABLE `geo_ip_city` ( `id` INT(5) UNSIGNED NOT NULL AUTO_INCREMENT, `begin` BIGINT(20) NOT NULL DEFAULT '...
7
votes
1answer
271 views

Query optimizer recommends adding index instead of using existing index

I am trying to determine why the query optimizer in SQL Server is recommending creating a new index instead of using an existing index that appears to be sufficient for the query. First the table. ...
5
votes
1answer
153 views

Indexes: integer vs string performance if the number of nodes in the index is the same

I hope this is the right place to ask! I am developing an application in Ruby on Rails with the PostgreSQL (9.4) database. For my use case, columns in tables will be looked up very frequently, as the ...
4
votes
1answer
115 views

Microsoft SQL Server 2016 performance degradation for stored procedure called 1000's of times

Context : Small table, stored procedure to update table, first two thousand hits no problem. After those first hits it starts to crawl to a snails pace. This stored procedure has no problems in our ...
4
votes
2answers
5k views

Will altering order of columns in GROUP BY affect performance?

I have a SQL query like this: SELECT A, B, (CASE WHEN C=0 THEN 0 ELSE 1 END), COUNT(D) FROM SomeTable GROUP BY A, B, (CASE WHEN C=0 THEN 0 ELSE 1 END) On a huge dataset the actual execution plan ...
4
votes
2answers
2k 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 ...
4
votes
1answer
187 views

Fast alternative for “NOT IN”

I have a table A that got a field called id that is the primary key of this table. I also have a table called B which also have a field called id as primary key. Now I want to get all rows from ...
3
votes
2answers
220 views

Joining two Mysql VIEWs takes a very long time

I have a textbox (for which I used jQuery auto-completion) in my PHP form where user can insert an actor/actress name and then by clicking "Search" button, a new window is opened showing list of ...
3
votes
1answer
60 views

Query Plan Error

I have an interesting situation. I use SQL2014 Enterprise version with SP1. The following query results an error message : The query processor ran out of internal resources and could not produce ...
3
votes
1answer
738 views

Getting each status change in a table

I have a table that holds status changes per item. The item can go in and out of a status multiple times. ItemTable (ItemId int, Status varchar(50), DateOfChange date) I need to pull the date of ...
3
votes
3answers
3k views

Speed up search across multiple columns

We have a table: user_info (user_id,domain_id,first_name,middle_name,last_name,work_place,.,.,.) Now, we have a user search that search across three columns first_name,last_name and work_place. ...
3
votes
1answer
1k views

Is there any way to get the estimate cost of executing a query in MySQL?

In PostgreSQL, EXPLAIN or EXPLAIN ANALYZE will show the estimate cost of executing a query. But EXPLAIN in MySQL doesn't provide this information. How can I get the estimate cost without installation ...
2
votes
2answers
144 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 SSF....
2
votes
1answer
126 views

what would be a good choice of clustered index (and other indexes) for this situation involving a indexed view?

To help me improve the performance of some queries I have created the following indexed view: CREATE VIEW DBO.vwOrders WITH SCHEMABINDING AS /*-------------------------------------------------------...
2
votes
1answer
4k 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
votes
1answer
137 views

Several values from different tables

I'm totally lost here and not know how to get this to work and hope any can help me here. I have several tables: default_users, default_profiles, default_status, default_comment and latest ...
2
votes
1answer
94 views

Computational power required for this query

I am not sure if the query I am trying to run is unreasonably large, in terms of computational power. The query will identify islands (and their duration) of a certain condition in my db. Things work ...
2
votes
3answers
358 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
votes
0answers
217 views

Get all comment.message, status.message, users.* and profiles.* where users.user_id exists in friend.friend_id or friend.user_id

I need some help building this query because it's a bit complicated at least for me. I need to get all comment.message, status.message, users.* and profiles.* where users.user_id exists in friend....
2
votes
0answers
40 views

Composite index works for larger set of data, but not smaller

This is a follow on question to optimise my.ini for key query Data model: DROP TABLE IF EXISTS `contract`; CREATE TABLE IF NOT EXISTS `contract` ( `id` int(11) NOT NULL AUTO_INCREMENT, `...
2
votes
1answer
6k views

MySQL SUM with multiple GROUP BY on same table

What is the best way to produce several sum results based on different group by conditions on the same table in MySQL? I believe I'm doing a bad select, but I can't figure out a better way. Imagine ...
2
votes
1answer
188 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
1answer
522 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
428 views

Row with latest timestamp

How to get the row with the latest value in a TIMESTAMPZ column? Is an index needed? Does an index change the strategy? Would behavior vary by database (I'm using Postgres 9.4)? My app records data ...
1
vote
2answers
1k views

Mysql. Block/disconnect slow queries

I am experiencing issue. Someone 'attacked' my server: simply by searching the same phrase with multiple requests. As it is text search request and database indices are not used, the engine searches ...
1
vote
2answers
291 views

Need some support on MySQL Query

I have a query SELECT leads.id, sfav.id is_favorite FROM leads INNER JOIN teams tst ON tst.team_set_id = leads.team_set_id INNER JOIN members members ON tst.team_id = members....
1
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1answer
63 views

Update records from one table to another in different databases where condition is accomplish

I have two tables stored in two differents DBs and I need to perform some sync between both tables based on lastmodifieddate and lastSyncAt. Let's call them as db1 and db2. This is the DDL schema for ...
1
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1answer
27 views

index creation - Slow Query - PostgreSQL 9.2

I've got the following query: SELECT * FROM ( SELECT split_part(full_path, '/', 4)::INT AS account_id, split_part(full_path, '/', 6)::INT AS note_id, split_part(full_path, '/', 9)::TEXT ...
1
vote
1answer
98 views

Why SELECT is so slow

I have the following table CREATE TABLE words ( id bigint(20) NOT NULL, `text` int(11) NOT NULL, w1 int(11) NOT NULL, w2 int(11) NOT NULL, w3 int(11) NOT NULL, w4 int(11) NOT NULL, ...
1
vote
2answers
3k 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, ...
1
vote
1answer
234 views

Slow queries InnoDB occasionaly

I have the next table: CREATE TABLE `sessions` ( `session_id` char(32) COLLATE utf8_unicode_ci NOT NULL, `session_expires` int(11) NOT NULL DEFAULT '0', `session_data` varchar(10000) COLLATE ...
1
vote
1answer
48 views

optimise my.ini for key query

I have a database system with a fairly complex dashboard query. First of all the details. Data model: DROP TABLE IF EXISTS `contract`; CREATE TABLE IF NOT EXISTS `contract` ( `id` int(11) NOT ...
1
vote
2answers
109 views

OrderBy int slow for large table join

I have roughly 1.5 million records. This query works fine for smaller data, but it gets a second slower for every few hundred thousand records. For 1.5 million, the query is noticeably struggling. I ...
1
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3answers
515 views

Slow query when adding additional where clause

Here's my setup (Postgres 9.3) Posts project_id Messages post_id kind updated_at I'm trying to get the most recently updated 100 messages that belong to posts (on a specific project) that are ...
0
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1answer
67 views

Hashed and heap indexed object storage table insert and query performance

This question is partly to ask advice and assure this design is sane. I state the the desired properties upfront here, then go in more detail in the rationale and follow up with the design and example ...
0
votes
4answers
314 views

Single SQL query to retrieve data in a particular order (not ASC/DESC)

I have a MySQL table, let's say called reviews review_id, product_id, language_id, rating, review, author language_id ranges from 1 to 10 for 10 different languages. Let's say I determine that my ...
0
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2answers
2k views

How to get rid of using temporary when using DISTINCT in MySQL?

When I do the following, I get Using where; Using index; Using temporary. How do I get rid of Using temporary? http://sqlfiddle.com/#!8/f61a2/3/0 CREATE TABLE `test` ( `a` varchar(45) NOT NULL, `...
0
votes
3answers
97 views

How to return last used record?

I have simple table called ips with 2 field ip and address, which schema is following CREATE TABLE IF NOT EXISTS `ips` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `address` varchar(255) ...