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

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2k views

How to use LOW_PRIORITY for heavy queries?

I have scheduled heavy UPDATE queries at administrator level, and since they are heavy UPDATEs with multiple JOINs, consume a huge amount of resources. I do not want them to stop end users from ...
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1answer
81 views

Query tuning - performance

Could you please help me tune this query. It takes over half an hour to run! I want to identify repeat bookings (can only be identified using an annoying varchar field - email) UPDATE #Repeats --a ...
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1answer
1k views

Using OFFSET in a large table by a simple sub-query

The slow performance for using OFFSET in large table has been widely discussed in various blogs, and the most efficient way is to use an INNER JOIN as SELECT * FROM table INNER JOIN ( SELECT id FROM ...
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1answer
419 views

Identical query, tables, but different EXPLAIN and performance

I have two tables levels and users_favorites +--------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | ...
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1answer
1k views

SQL Server performance for tables having large number of columns [closed]

I have a requirement where I need to create a table with about 600 columns. Out of 600 columns about 200 columns will be XML columns. Other column will be of other datatypes such as int, varchar, ...
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1answer
5k 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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2answers
257 views

MySQL (InnoDB) UPDATE SET performance with value in WHERE AND clause

If an UPDATE query is performed where the values being SET are also part of the WHERE clause, in the form of an additional AND statement on the column being set's value, is there a significant ...
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2answers
7k views

INSERT INTO with SELECT subquery db2 9.5

I have the following query that takes 4 seconds to execute: SELECT TX.* FROM TABLE_X TX INNER JOIN TABLE_Y TY ON TY.VALUE_ID = VALUE_ID_IN AND TY.PROD_ID = TX.PROD_ID WHERE (TX.PLACE_ID1 ...
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1answer
577 views

“copy to tmp table” for 24 hours, then timeout; when ALTERing to add PK & AI

I downloaded the Wiktionary XML dump, and ran mwdumper.jar to insert the data into MySQL. Following the advice in the manual, I commented out the PRIMARY KEY AUTO_INCREMENT part of the CREATE TABLE ...
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3answers
2k views

Oracle query is slower the second time

I have a general question about something I'm seeing in performance tuning in Oracle. I have a query that I'm testing. It's too big and complex for me to provide a simple example, sorry! (I tried ...
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1answer
61 views

What ways are there to limit the processor / ram requirements of a specific query?

Every once in a while, I need to run some very expensive query on a production server. Think spaghetti joins. This is likely to affect the server operation, and I don't want that. What ways are there ...
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1answer
4k views

Get top most parent by nth child id?

Now there is a question we commonly use this technique to maintain the parent child relation i.e we store all the entities in one tables with a parent_id column and all top most parents have 0 in the ...
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2answers
1k views

Obvious inefficiencies in this Netezza query?

Why might this query be taking nearly 2 hours to run when similar queries complete within a minute? CREATE TABLE T3 AS SELECT A.*, COALESCE(C.FIELD1,0) AS FIELD1A, ...
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1answer
31 views

Simple query not using indexes

My query is not using indexes. It is a simple query. Can someone explain why that's the case? The query: select TIME_FORMAT(start_time,'%H:%i') start_time, TIME_FORMAT(end_time,'%H:%i') ...
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1answer
226 views

Avoiding performance hit from GROUP BY during FULLTEXT search?

Is there any clever way to avoid the performance hit from using group by during fulltext search? SELECT p.topic_id, min(p.post_id) FROM forum_posts AS p WHERE MATCH (p.post_text) AGAINST ('baby ...
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1answer
325 views

Simplify and optimize a complex query

Our site has a chronological event feed that uses MySQL. We have noticed that some of the queries tend to run for quite a bit longer than others. For example, some queries for our heaviest users take ...
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1answer
2k views

Query performance of a NULL vs an empty ('') varchar in SQL Server 2012

I have 3 indexed fields in a query: int, int, and varchar(250). The query performs well when all 3 conditions are specified with real values. The int columns always have values, but there are plenty ...
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1answer
384 views

Query tuning help needed (Hash Match and Table Scans)

I need help optimizing the following query (returning ~8k rows): SELECT A.sys_id, 'AppSvrRels' = CAST(SUBSTRING((SELECT (', ' + T.name) FROM ( ...
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1answer
2k views

Slow complex query with group/order

I have a problem with a very important query in my application. It is very slow when adding group and order to it. So the full query is: SELECT m.id, m.title, m.title_text, ...
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1answer
229 views

What would be a optimal index for this query in mysql

I'm trying to optimize this query. SELECT * FROM sales_reps WHERE account_id = 1 AND (state = 'enabled') AND (clients >= 5 OR revenue >= 10000) ORDER BY name, platform, client_group, ...
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2answers
619 views

Simple queries taking ages to run after changing from MyISAM to InnoDB

I have a quite large (300GB) table on MyISAM, which I've "converted" to InnoDB, and performance for a specific query has dropped through the floor. When I say "converted", I can't afford to take the ...
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1answer
174 views

Get and count all blog posts and all users that fits a LIKE condition (two sepparated queries)

I've this tables: -- -- Table structure for table `default_cmvblog` -- CREATE TABLE IF NOT EXISTS `default_cmvblog` ( `id` int(11) NOT NULL AUTO_INCREMENT, `title` varchar(100) COLLATE ...
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1answer
3k views

PostgreSQL 9.1 - Query on VIEWS taking a lot of time

Using PostgreSQL 9.1, we are having problems while executing queries on a VIEW of PostgreSQL. Following is the situation: We have a partitioned Table "buz_scdr" over which we have built a VIEW ...
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1answer
155 views

Reviewing all new MySql queries on staging environment

The problem I am trying to solve: It's well known that not all developers know what is EXPLAIN in MySql, and not every knows how to use it. Large part of them consider MySql as a black box, no matter ...
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1answer
44 views

Get wall_post and profile data for several users

I'm trying to build a query for fetch wall_posts and profile fields for several user_id. First see the images at: http://www.dropmocks.com/mBjQ7P. The table with id_user_rq, id_user_ap is the table ...
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1answer
217 views

MySql - How can I improve this query?

I have the following table: http://pastebin.com/XH6FvhZ8 and the following query: SELECT * FROM (SELECT * FROM `job_logs` ORDER BY id DESC) AS job_logs_tmp WHERE (job_logs_tmp.user_id = ...
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1answer
522 views

Oracle Benchmarking (SQL_NO_CACHE …)

I want to benchmark some queries on an oracle System from a JDBC application. However, the database seems to cache at some point in time. However, this is not intended in this case. Is there ...
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2answers
131 views

Improving MySQL efficiency

I have a table now containing over 43 million records. To execute SELECT, I usually select records with the same field, say A. Will it be more efficient to divide the table into several tables by ...
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0answers
25 views

Update queries randomly slow on INNODB Mysql

I have been struggling with a slow update query. Have already tried using indexes and other query optimization techniques. I have been using MYSQL database with INNODB engine. The issue is that, ...
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1answer
45 views

Slow MySQL query when the IN list is long

I have 3 tables, namely: product, product_has_category, category: CREATE TABLE IF NOT EXISTS `product` ( `id` int(11) NOT NULL, `name` varchar(255) DEFAULT NULL, `des` text COMMENT 'description', ...
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1answer
37 views

Monitoring SQL Server 2012 slow queries/queries which are causing blocking

I am using SQL Server 2012 and I want to get hold of the queries which are taking longer to execute along with the queries which are causing blocking on the server. When I look at the server for the ...
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0answers
46 views

Tuning MySQL MyISAM for large joined updates

I have a database with two tables that I would consider small. I need to update values on the larger of the two tables (1,100,000 rows, 75M MYD, 120M MYI) from the join of the two tables. The smaller ...
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1answer
47 views

MySQL Query with good execution plan is very slow due to Sending data operation

I have the following query: SELECT a.borrowerId AS borrower_id, a.created, NULL AS initiator_team_id, NULL AS initiator_user_id, NULL AS old_team_id, NULL AS old_user_id, ...
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0answers
11 views

Optiming ACT_RU_JOB Query

We're using Activiti version 5.15.1 with timers in our workflow which sends reminders to users who are in the workflow. Problem is that we're creating jobs in ACT_RU_JOB table and even though there ...
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1answer
30 views

Procedure to read from crontab like table and populate another one periodically

Postgres 9.3 Debian 7 I'm working on a mobile game project (poker like) where an admin user can register a recurrent tournament. As it's recurrent, I modeled it crontab like as follows. ...
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1answer
55 views

Query or a New Column for Performance

I have below tables: ProductsTable (has product details), UsersTable (has all application users), RatingCategry (category for which user can rate a products like Quality, Cost etc.) and ...
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2answers
67 views

Should I stop an awfully inefficient MySQL DELETE statement?

I'm running the following statement on MySQL 5.5 in a 1GB 1CPU SSD virtual machine from Linode: DELETE table FROM ( SELECT MAX(id) id, field FROM table GROUP BY field ) temp_table INNER ...
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0answers
58 views

Select SQL_Calc_Found_Rows query extremely slow

I'm Wordpress 4.2.2 on an Ubuntu 14.04 LTS server, with PHP 5.9x and MariaDB 10.0.17. When clicking on a post on my site I see many slow queries that all resemble this and it ends up taking as 8 or 9 ...
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0answers
31 views

Delete using join or using sub-query?

I need to delete rows from a table based on what is present in a temporary table. For me, both of these statements work : DELETE from main_table where `id` in (select `deletable_id` from ...
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0answers
60 views

Query execution taking long time

SELECT sqltext.TEXT, req.session_id, req.status, req.command, req.cpu_time, req.total_elapsed_time FROM sys.dm_exec_requests req CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS sqltext select ...
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0answers
224 views

INSERT INTO with TABLOCK taking longer than without TABLOCK [closed]

I'm doing something like below to ensure the insert is minimally logged: insert into AnotherDatabase.dbo.HeapTable with (Tablock) ( <column fields ) select <column fields> from ...
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100 views

How to speed up for huge tables in SQL select query?

I have the following huge tables. Table_1 with 500000 (0.5m) rows Table_8 with 20000000 (20m) rows Table_13 with 4000000 (4m) rows Table_6 with 500000 (0.5m) rows Table_15 with 200000 (0.2m) rows ...
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1answer
58 views

Why MySQL SELECT performance depends on table size? [closed]

I've got two identical tables with the following structure: 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 ...
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0answers
86 views

Most effective way to manage a growing list of time series data in an MS Access database

I am building a database to store time series data along with some other summary statistics. Since this is a local application I do not have access to more robust database solutions and am confined to ...
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48 views

PostgreSQL DB freezes with large inserts

I am developing a web application with an SQLAlchemy ORM linked with PostgreSQL database backend. I have this usecase where a client uploads a file of about 20 MB containing large data. What I am ...
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75 views

Query Performance - Why is a query slower when there are two criteria on the same column?

I have these two queries against a view, where I've added WHERE clauses against a date column (Indexed, Unique, Non-Clustered, Ascending): SELECT ColA FROM MyView a WHERE a.[Date] >= ...
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1answer
211 views

MongoDB document size for collection - impact on RAM and query performance

I have been advised on stackoverflow to ask this question on dba.stackexchange instead - We are using MongoDB version 3.0 with WiredTiger storage. As newbies to MongoDB, we may have designed our ...
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0answers
57 views

Is there a way to improve this query further?

I've got a query that over time I've been improving. Originally it simply selected * from the records table, and the data was formatted on the webapp side. But that was slow and I wanted to make ...
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1answer
55 views

placing conditions in a join query join on vs where

Is there and advantage to one of the following options over the other or are they the same ? select * from T1 Join T2 on T2.id=T1.t2_id and T2.field=value; vs. select * from T1 Join T2 ...
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0answers
46 views

Poor performance filtering mysql spatial join

First of all, sorry for the crossposting. I ask this question in stackoverflow and they sent me here I have a mysql table with spatial references (GEOGRAPHIC_FILTER), like cities, countries, natural ...