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

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94 views

Dealing with large log files

I'm new to the database world and have recently started working with a large database with several tables with mainly varchar text and integers. The two largest tables are of ~50 million and 25~...
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208 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
207 views

EXISTS and sub-query cost

i've just wondered if there's a difference in cost(memory,cpu) of an EXISTS or NOT EXISTS in following queries. Does it make a difference if i select NULL, 1 or columns? 1) SELECT id FROM Parent p ...
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448 views

SQL Server 2012 Performance Test

I've been given a task to test where an SQL Server 2012 can achieve better performances - we have two options: Use the SQL Server as an On-Premise machine (Standalone server that we have) Use the ...
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1answer
1k views

Slow performance of MySQL Join Query

I have inherited a site (running Coldfusion8 and MySQL 5.0.88) with a product search using multiple criteria. I'm struggling with optimizing the search, especially a pricelist check, which makes the ...
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2answers
183 views

Can a poor database layout cause performance issues for simple queries?

I have a database layout that is realy a mess and needs to be optimized. Does the layout of the database and some queries that are executed cause other queries to be slow too? For example, an insert ...
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2answers
1k views

Update Large Table

I have these two tables: user_profile: user_profile_id_int int primary key user_profile_id varchar user_activity: user_profile_id_int int key user_profile_id varchar both fields in user_profile ...
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1answer
83 views

Why using where in indexed field is slow?

we have a big table. the table structure is : CREATE TABLE `visit_logs` ( `id` int(10) NOT NULL AUTO_INCREMENT, `user_id` int(10) NOT NULL, `ref_id` int(10) NOT NULL DEFAULT '0', `link_id` ...
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2answers
81 views

How can I improve performance on a 3 table query?

I'm attempting to analyze a resource drawdown (the percentage of time individual units are being utilized during a reporting period, e.g. 2-weeks or 1-year). I need the aggregation down to the minute....
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1answer
66 views

Extra fields in user_role / roles tables or a new table

I have a user_roles table which I use to manage permissions and user's access to certain things. For example, a team manager is a role. Since a team manager belongs to a specific team, the way I ...
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1answer
90 views

get query execution time in command prompt [duplicate]

I'm doing this query select * from rentals. This table has more than 10,000 rows and it takes more than 4 minutes to retrieve the results. But I get this time after I get the results: 10000 rows in ...
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1answer
84 views

MySQL difficulty with optimizing slow query with index but without improvement. Explains tells otherwise

I've a slow query (~11 seconds) that I'm trying to optimize. But the use of indexes seems to not make any difference even thou Explain indicates otherwise. Let me walk you through my problem. So this ...
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1answer
47 views

How can I 'further' improve my table and queries

This question is an extension of this question. Where Rick James kindly provided a list of things I should change in my table and query. I also changed my application so that unused filters weren't ...
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1answer
111 views

SELECT Causes Performance Issue [closed]

I have a SQL SELECT statement that has joins on 27 of our warehouse tables. Original statement was taking more than an hour everyday so I decided to optimize it. I created some indexes but still it ...
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1answer
27 views

What are the consequences of enabling slow_query_log and flushing the cache on mysql?

I have a large database that is performing poorly recently. I want to enable the slow_query_log to investigate the queries and flushing the cache but I need to know what are the consequences of doing ...
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1answer
67 views

Does InnoDB store row counts in secondary index B-Tree non-leaf nodes?

Does InnoDB store row counts of child nodes in secondary index B-Tree non-leaf nodes? If so, does MySQL use this information to speed up COUNT(*) queries with range constraint (assuming appropriate ...
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2answers
412 views

Slow SQL query with LEFT JOIN

What my query is doing: I have two SQL tables and I want to copy datarows from the one table to the other table. I am doing this for statistics. The source table includes all current member-sessions/...
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1answer
107 views

Speed up COUNT(*) when using an index

I have a table similar to this (simplified): CREATE TABLE books ( id INT AUTO_INCREMENT, category INT NOT NULL, PRIMARY KEY (id), KEY (category) ); This table has over 10,000,000 ...
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1answer
155 views

Calling a View from Procedure

I have a Large SQL Statement with several Join which need to be executed with different Where Conditions based on Procedure Input Parameters. Ex: CASE pSearchType WHEN 1 THEN SELECT Col1, ...
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1answer
72 views

How can I improve this query in PostgreSQL?

I've been using PostgreSQL for a little over a year. I am continually whacked by queries that have counts in them, such as: SELECT COUNT(*) AS count_all, listings.id AS listings_id FROM "listings" ...
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2answers
84 views

Is there's another function to optimize this query in MySQL?

I want to use a function that returns for me the same result in one line is that's possible?? MIN( CASE WHEN (data.pro LIKE '1 %' ) THEN 1 WHEN (data.pro LIKE '2 %' ) THEN 2 ...
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1answer
223 views

Why isn't Postgres doing an index-only scan?

I am using Postgres 9.4. This is my table: id | integer | not null default nextval('frontend_prescription_id_seq'::regclass) presentation_code | character varying(15) ...
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2answers
39 views

Two (almost) identical queries, but only one of them uses the index

I have a table with two columns, batch_id and study_id. There are indexes on both columns. I want to get a random row back from MySQL. I originally wrote: SELECT * FROM alt_join_batch_study ORDER BY ...
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2answers
257 views

Viewing execution plans for queries with parameters

I have a sample query generated by an application (Microsoft Dynamics AX 2012 in this case) which is ineffective performance-wise (cross joins, order by etc.) I would like to display its execution ...
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1answer
92 views

Auto update stats turned off for a user database on SQL Server

While trying to improve the performance of few queries, we found via execution plan that there were lot of index / clustered index seeks. Therefore: First thing we did, was to check our Re-indexing ...
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1answer
51 views

Can I use SPARSE somehow on a non-nullable bit column with mostly false values?

I have a table that stores the results of queries that are run at least once a day. There's a bit column that represents whether the row is from the most recent run of a particular query with a ...
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1answer
88 views

Query performance issues

I need help in improving the performance of the following query. It has the purpose to select one record out of a group of records with an identical ID (doublettes). Rules are that Date2 must be the ...
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2answers
160 views

Fourth inner join to the same table increases query duration significantly

As soon as I add a fourth inner join to a specific table, the query duration increases significantly: sub 1sec to 45sec. The table in question is deployments d4. The SQL Query: select a.id as ...
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3answers
80 views

Performance first low, then high after adding index, then keep high after drop index

I am testing performance a complicated select query. It is very slow. using explain, I have found a ALL in type COLUMN. Then I ADD INDEX. result comes out fast. However, when I DROP the INDEX I ...
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1answer
195 views

SQL : get rows from two tables relatively

I've two tables named categories and products. Simple structure is given below. categories cat_id cat_name 1 c1 2 c2 3 c3 products prod_id ...
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1answer
38 views

How can I speed up this simple query

I am trying to speed a query that grabs data to be used to display a graph for a research project. It's currently VERY slow. It has 18295603 items only and takes about 20s per query. Here is an ...
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1answer
868 views

MongoDB performance problem

I have a MongoDB for storing result like this {_id, type, imei, lat, lng, spd, dir, time} {_id, type, imei, lac, cid, time} If type is f first one is used and if it is l second one is used. Here ...
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2answers
113 views

Is there a more efficient way to run this query for first/max transaction?

For each account, I need the first transaction date, the largest transaction amount, and the time taken to get from first to largest. Data is truncated and reloaded frequently, and I have read-only ...
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1answer
72 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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1answer
507 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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1answer
141 views

Performance issues when extracting scatter plot data

First off: Sorry for the title, couldn't think of anything better. Feel free to change it though. Ok, assume I have the following table: -------------------------------------------------------------...
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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
370 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
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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1answer
3k 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, SUM(h....
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2answers
628 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
7k 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
401 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
76 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
532 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 `a`.`...
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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 ...