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

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1answer
88 views

Any idea why this seemingly-simple query is really slow?

Here's the query SELECT count(*) FROM registration r LEFT JOIN registration r2 ON r.baggage_group_id = r2.baggage_group_id AND r2.team_id IS NULL WHERE r.event_id = "102577"; It seems pretty ...
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2answers
335 views

What's the best way to translate a website [closed]

I have a website in Django using MySQL, and I have more than 4.000 entries that I want to translate. What's the best way to do it? Create a new database for every language? Create other table for ...
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2answers
3k 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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1answer
2k views

Poor performance on inner join using dates and between

I am having trouble optimizing a query that does an inner join using a date range. The purposes of the query is take daily data and summarize by week. Select pcw.EndDate WeekEndDate, h.Store, ...
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2answers
583 views

Indexing varchar column to search for first letter

I'm trying to optimize a legacy web-app where users can ask for a list of all records whose name starts with a given character. The query to optimize is: SELECT oggetto.id_oggetto, titolo, anno, ...
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1answer
6k views

Different execution plan for the same query if I change a value in the predicate

I am getting two different execution plans for the same query only by changing the value in the predicate, the first one uses nested loops and the other one hash join which takes a lot longer. ...
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1answer
393 views

MySQL Query Optimization - Indexes & Joins 12 million+ records

I'm running the following query: SELECT `track_title`.`title`, `track`.`id`, `artist`.`name` artist, `album`.`title` album, `st_tag`.`tag`, `track`.`year` FROM `track` ...
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2answers
162 views

Improving performance of query with `WHERE <> ''`

I have a qeuery that checks where two columns are not '' (blank) - [blank and NULL are not the same in this case] Is there any way to improve the performance of the query SELECT * FROM myTable WHERE ...
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1answer
75 views

Does limit impact affected rows or not?

I have this table: CREATE TABLE IF NOT EXISTS `usergroups` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT, `user_id` int(11) unsigned NOT NULL, `group_id` smallint(5) unsigned NOT ...
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2answers
2k views

Improve performance with the WHERE NOT IN sub-select clause

In the following query, I have to count transactions for each customer. [EDIT]However, I have to exclude from the result set entirely, customers that have a transaction older than one year. ...
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1answer
81 views

Query for View with unique entries from Database with repeated entries

I have a table with columns of Hotel names, city name and country name (of the respective hotels). I need to create a view of unique entries which will contain city name and country name columns. Any ...
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1answer
492 views

MySQL: COLLATE performance

I have a table called users with a column firstname and with collation utf8_bin I want to know what happens under the hood when I execute an query like: SELECT * FROM `users` `a` WHERE ...
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1answer
86 views

Query optimization when no row is returned

I am using explain to figure out what is happening in my query which is: explain select t from c where u1_id = 1 group by t; I see "Using where" in the Extra column of the resultset. But this only ...
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2answers
93 views

Database and query optimizacion

I have a database containing three tables: tbl_database (main table is the primary), tbl_cmdatabase and tbl_blacklist. The three tables share the same structure but differ in the number of records ...
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1answer
496 views

Design database to query a date range for scheduling

I am designing a db that should include a table with fields for datetime scheduling, so as I know what kind of queries will be made​​ periodically I would like to design the table for them to be as ...
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1answer
200 views

Topics and posts represented by one table or two?

I'm currently building a forum component for a larger application and I'm considering different approaches to certain parts of the database schema. In particular, I am considering representing topics ...
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1answer
98 views

What is the best relationship model for high performance?

I want to model a relationship between Customer and Transaction. However, because Customer is only described by a unique string and no extra info, I have two possibilities to implement it in the ...
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2answers
117 views

How can I improve this query

I have the following table: CREATE TABLE `twitter_relationships` ( `id` int(11) NOT NULL AUTO_INCREMENT, `user_id` int(11) NOT NULL, `source_twitter_id` bigint(20) NOT NULL, ...
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1answer
38 views

Can the subquery be simplified/optimized?

Here's a simplified version of a query I run. I've removed a bunch of key/value pairs for simplicity. The constraint is that I can't change anything outside of the ARRAY function; but the ARRAY ...
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1answer
11 views

Joining on a M-N lookup table vs keyword searching a single column

I am in the process of writing an image gallery webapp similar to that of Danbooru, and in the process, decided to take a look at danbooru's database schema for an idea about how things are ...
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1answer
85 views

Most efficient way of finding rows in a table that don't exist in another — SQL Server

What is the best method of finding rows in table A that don't exist in table B based on unique key of the tables, when both tables are huge (A over 300 million rows, B over 500 million rows) and the ...
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1answer
37 views

Slow Query Postgres 9.2

I've got the following query: SELECT j.id, concat(c.company, ' ', c.name_first, ' ', c.name_last) AS client, c.email AS client_email, ...
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2answers
55 views

Check existence on other tables: performance advice

This is my first post. I have this data model: I want fetch some profile, with checking if they have any page or user assigned or not. I have tried multiple queries and finally came to these tows: ...
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1answer
92 views

Slower running Query with better Filter?

mysql> SELECT * FROM history_uint h WHERE h.itemid='1825689' ORDER BY h.clock DESC LIMIT 2 OFFSET 0 ; Empty set (0.00 sec) Explain: id: 1 ...
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1answer
119 views

Subquery ORDER BY doesn't work on MySQL 5.6, but works on 5.5

I try to join 3 tables (products, prices, categories) together to get a result of latest & lowest prices from the joined tables. I was able to get the expected result on MySQL 5.5, but after ...
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1answer
117 views

Vertica performance on select from view with union

We have a huge number of rows(tens of millions), and for each table we have an associated view that is a select with UNION ALL between that table and several others. Now, we are doing a select from ...
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1answer
79 views

How to increase performance of UPDATE of ~ 50.000.000 entries

We have a query that uses a temporary table to update certain columns in the database: CREATE TABLE #NEW_OLD ( NEW nvarchar(20), OLD nvarchar(20) ); INSERT INTO #NEW_OLD VALUES ...
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1answer
48 views

Performance issue using view vs. direct statement

I have a table with structure similar to this: table values ( id1 int, id2 int, value real, value_at timestamp, constraint primary key (id1,id2,value_at) ) I need to get the "current value" for a ...
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1answer
76 views

Decrease Query Execution Time

I have been having issues with 2 queries with query execution times up to 250 seconds for each query. The tables joined have each less than 10,000 rows, with exception to 2 tables that have around 60k ...
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1answer
338 views

MySQL performance issue - intermittently slow queries

I manage an intranet application used by around 50 staff in a few locations. The application is hosted on a Windows Server 2008 VM with 8GB RAM and MySQL (5.5) is running on the same server as IIS. I ...
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1answer
70 views

Optimize slow query

I have this query that takes over half an hour to run on our Linux MySQL db... SELECT ls.emailaddress , lse.subscriberid , lse.eventtype , count(lse.eventtype) as total FROM ...
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2answers
52 views

DB select query performance when queried by partial key of primary key [closed]

My primary key is composite - {a,b}. Will there be any performance gain if I query only {a} or DB is going to scan the whole table as there is no index only on {a}. How much storage overhead would be, ...
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1answer
70 views

Is it more efficient to union from sub-query or combine two outer queries?

I searched for this but couldn't find the response I needed. So my apologies if this has already been asked. I'm asking in regards to DB2 but I suppose this would apply, generally speaking, to just ...
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1answer
61 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 ...
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1answer
88 views

Why is MariaDB 10 refusing to use my index on a date field?

I have the following table definition: CREATE TABLE `bets` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `id_mp` bigint(20) NOT NULL DEFAULT '0', `coin` char(3) COLLATE utf8_unicode_ci NOT NULL, ...
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1answer
81 views

Postgres not using the index even when rows returned is 5% of the table

I have a postgres table with the following structure: +---------+-------------+-------------+----------+---------+---------+ | id | timestamp | numvalues | text1 | text2 | text3 | ...
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1answer
95 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, ...
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2answers
126 views

Awful execution plans after migrating from MySQL 5.5.11 to MariaDB 5.5.41

We just migrated our web site database from a server running MySQL 5.5.11 to one running MariaDB 5.5.41. Everything is working mostly fine, except there's at least one query from our storefront that's ...
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1answer
90 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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1answer
192 views

Postgres - Insert performance with indexes

We have a table with about 20 columns in a Postgres 9.2.10 DB. For better performance on some SELECT queries, we plan to add an index on one column with data type timestamp. As the index also can slow ...
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3answers
134 views

Special function slow in where but not in select

I have kind of a special problem using a levenshtein algorithm in MySql. But I don't think that it's special for levenshtein. This query: SELECT *,levenshtein(word,'Facbook') FROM Words WHERE ...
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1answer
292 views

set global variable parameter?

My prod_server version is 5.1.47 and want to set the slow query log dynamically for certain period of time. I refered one site(http://toastergremlin.com/?p=276) there is mentioned below 5.1.6 we need ...
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1answer
145 views

intermittent performance issue - query with multiple CTE and trashed execution plan

I'm trying to optimize a SQL query that shows variable performance (less than 2 to more than 15s). Overview This is a ColdFusion website, with a SQL Server 2008 R2 backend The query is part of the ...
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1answer
2k views

Optimizing Amazon RDS - MySQLTuner Recommendations / Feedback & Suggestions

I'm currently trying to optimize a database I've inherited for speed. The server is an Amazon RDS db.m3.large instance: 2 VCPUs 7.5 GB Memory 500 GB HDD My current strategy is to do the ...
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1answer
100 views

Best approach to get last value inserted

I have several devices that report via Edge network their position (and more data) to a UDP server which directly inserts this data in a SQL 2008 r2. I want to know which is the best approach to ...
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1answer
63 views

Taking the difference in timestamps between successive entries

This is my first foray into DBA.stackexchange, so I'll say up front: this is a query optimization question. If this is not an appropriate question for DBA, let me know and I'll skulk away quietly... ...
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1answer
48 views

How to query a list of all the different errors?

I have a DB which is very big and stores a lot of eventlogs, around 15 million rows. When I try this query, it is totally impossible to get some results. Any idea how I could do this? Maybe indexed ...
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1answer
109 views

Summing a column based on uniqueness of another column without using temporary table

I have a table like this: CREATE TABLE `files` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `name` varchar(255) NOT NULL, `hash` char(40) DEFAULT NULL, `size` bigint(20) unsigned DEFAULT '0', ...
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1answer
423 views

Deciding which MySQL execution plan is better

Background: I have a query that I'm trying to speed up, involving 3 tables: omgenvelope has 5 million rows omgcust has 195 rows omginput has 35836 rows I'm obtaining the distinct omginputs ...
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1answer
1k views

How to optimize a very slow query with joins and group by?

I have this GTFS database : All the ***_id columns are indexed, and there are foreign keys between tables (such as a FK on trips.route_id to routes.route_id). So basically the link between a stop ...