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

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2answers
127 views

What is the performance difference between IN (42) and id = 42 in MySQL?

Are there any performance differences between SELECT * FROM table WHERE id IN (42); and SELECT * FROM table WHERE id = 42; ? The question is about just supplying a single value. The ...
0
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1answer
36 views

MySQL: What points should we consider when create composite index

There are multiple views behind the logic of creating composite index in a table. Creating composite index is obvious when we have composite primary key. Beside this, we create composite index on the ...
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2answers
51 views

How should I structure my time based index?

So I have this table in SQL Server 2008. Let's just say it's called TimeSheets. Now, that table has two columns I am concerned with. TimeSheetDate and UserCustomerKey. TimeSheetDate is a ...
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1answer
41 views

MySQL: Different thread states in Query execution

My MySQL 5.1 bases Intranet system is facing very bad performance during high load. When observe through MonYog, I found below thread states: We can simply understand the different thread state by ...
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2answers
205 views

Are there advantages to using temporary tables over derived tables in SQL Server?

I read the derived tables have better performance than temporary tables, but anyway many SQL Server developers prefer the second ones. Why? I must do queries with large data (millions records) and I ...
2
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2answers
314 views

Query hangs forever at first but works after one day

I have two schemas namely A and B. I regularly copy contents of 10 tables from A to B. Here's is how I do it First I rename the original tables in schema B Then, using SQL Developer I copy the table ...
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1answer
93 views

How to get query runtime in PL/pgSQL to be as fast as console query runtime?

Basically I want to assign the result of a query to a custom type attribute. However I noticed that querying directly from the PostgreSQL console was about 0.071 ms and inside the function was 0.400 ...
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1answer
138 views

What is the Difference between IN and Not IN performance wise?

I am new to database.I am having doubt that what is the difference between IN and NOT IN performance wise. When I am using IN, takes less time for the same query(Logically same query) when I use NOT ...
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0answers
24 views

Request for Help Optimizing a Query in MySQL

I have a query that is being used to report on the number of times a trigger in Zabbix, was fired by an event. For example, an event (not enough disk space) fires a trigger that sends an email to ...
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1answer
176 views

Improve Insert performance for 200 Million rows

How can the following insert statement be improved - which varies from 20mins on certain days to 70-140mins on most other days. SELECT DISTINCT od.SourceID, od.OrderID, od.OrderLineNo, ...
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0answers
100 views

Yet another slow query Postgresql 9.3

I'd like to get a count(*) from a relatively small joined table (returned result is about ~30000 rows). I use Postgresql 9.3 so simply getting select count(*) from tasks_task; uses index-only scan, ...
2
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2answers
82 views

Comparing Queries

In SQL Server, if you're comparing the statistics IO from two queries, how do you ensure that caching doesn't become a factor? For example (I'm making this up as I type, not a real example): SELECT ...
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1answer
88 views

T-SQL Optimizing a Join on TOP Value from another table

I've got a data warehouse that goes through a full refresh each night that can take about an hour to process 16 million rows/25gigs of data and we're looking for ways to reduce this time without going ...
0
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1answer
73 views

Database is slow once in a while

I am executing a web service for 100 times. The average response time of this service is 1.5 seconds. But when I look at the response time of each execution individually, there are a few executions ...
2
votes
1answer
80 views

Optimize table and query, aggregate by date or date-hour

I have a table storing sensor data (100M rows currently) from stations from different sites. In my case, sites may have many stations. Create table statement is as follows: CREATE TABLE sensor_data ( ...
2
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0answers
60 views

Does Oracle ADO.NET varchar parameter size influence query plan reuse?

I am considering to apply a fix which will generate constant parameter sizes for (n)varchar parameters. The application is based on NHibernate with the old OracleClientDriver (using Microsoft Oracle ...
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0answers
26 views

What Index can I apply to a GROUP BY, MIN() and WHERE MySQL Query

I have the following table: CREATE TABLE `wp_prize_draws_log_copy` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT, `pid` int(11) NOT NULL, `entry_date` date NOT NULL, `entry_time` datetime ...
0
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1answer
39 views

Does Oracle Partition by Reference optimizes join queries

Oracle 11g has a new feature in partitioning tables called partition by reference. I want to know whether Oracle joins (nested-loop-joins or hash-join or ...) rows from proper partitions when joining ...
3
votes
1answer
145 views

How to correctly return a query result only if it isn't NULL?

I'm writing a PL/pgSQL function that creates a cursor for a query that I need to check whether it returns something. What I'm doing is this: Run the query Check whether it returns something. If it ...
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0answers
43 views

MySQL aggregation count performance

I have a table with about 30 million records, and I'm doing a query where I can group by field Year and count the results for that year. The table structure looks like: id | year | amount The ...
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0answers
32 views

Mysql query getting hung!

I am using mysql 5.5. I create following temporary table: CREATE TEMPORARY TABLE IF NOT EXISTS tempdb.%s ( `count` int(10) NOT NULL, `m_class` enum('SMS','EMAIL') NOT NULL, ...
2
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0answers
37 views

Single table row “sharding/versioning” to customize values

Introduction Hello everyone, I have done quite a bit of searching and I cannot find a solution for my specific issue. There are a few factors that complicate my situation, which I have outlined ...
0
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1answer
13 views

Oracle Autodop disabled at the table level

I have a question related to Oracle auto DOP and parallel DML concepts. I have a scenario, if I set the Auto DOP set to 1 on the table and if I run parallel DML statements on that table through ...
1
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1answer
44 views

Poor query performance in MySQL

I have a 10 million record table in a MySQL 5.5 InnoDB. It's running in a 16GB RAM server with good CPU and fast HD. When I run the following query SELECT DISTINCT knowledge_id, ...
0
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1answer
43 views

Sql Server Full Backup Duration Increased Dramatically

since last week My Full Backup Increased dramatically .before last week the time is about 3 hour and now the time is about 6 hour.in addition some query take long time to run. (not all the query).I ...
0
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1answer
59 views

Slow MYSQL performance due to sub queries

Here is my query: SELECT BAL,NAME, (SELECT SUM(DR) FROM transaction WHERE NAME=TNAME AND DATE < '2000-05-01') AS DR , (SELECT SUM(CR) FROM transaction WHERE NAME=TNAME AND DATE < ...
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2answers
55 views

A simple database and Query System? [closed]

I am new to databases and trying to solve one problem in which I have to build a simple database having few entries and then querying that database and then recording that answers from the database. I ...
0
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1answer
41 views

Best Indexing Strategy for Query with Equality[A], Range[B], Group By[C], AND Order By[count(P)]

I have a poorly performing query: SELECT user_id, count(item_id) as count FROM table items WHERE category = 'magazine' AND created_at > 1384754400 GROUP BY user_id ORDER BY count(item_id) desc ...
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2answers
141 views

MYSQL - Why does this SELECT get slower the further down the table?

My table: CREATE TABLE `wp_users` ( `ID` bigint(20) unsigned NOT NULL AUTO_INCREMENT, `user_login` varchar(60) NOT NULL DEFAULT '', `user_pass` varchar(64) NOT NULL DEFAULT '', ...
2
votes
1answer
28 views

General purpose view for last value in a group

I am trying to create a view to show the last value in the group. Looking for a more general purpose query. CREATE TABLE a ( id INTEGER, seq INTEGER, val VARCHAR2(16), PRIMARY ...
2
votes
1answer
52 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 ...
1
vote
2answers
63 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, ...
0
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1answer
37 views

How can I efficiently search for all records from a given month, or a given year?

We have a couple queries that involve datetime fields. In particular, we are checking for things like SELECT field1, field2, ..., field20 FROM table WHERE MONTH(startDate) == 1 SELECT field1, field2, ...
1
vote
1answer
99 views

Slow running query with inner SELECT in where clause

I have a query that looks like the following: USE DATABASE3; GO SELECT t1.COL1 AS COLUMN1, t2.COL2 AS COLUMN2, t1.COL3, t1.COL4 AS COLUMN4, t1.COL5 AS COLUMN5, ...
1
vote
1answer
88 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 ...
1
vote
1answer
122 views

UPDATE a column by COUNT of another table

It might be a naive question, but what is the difference of these two queries and which is preferred? UPDATE table1, (SELECT id,COUNT(*) idcount FROM table2 GROUP BY id) AS B SET table1.Freq = ...
0
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0answers
82 views

Execution time vary for the same query

I have a query which looks like this: select * from ORDERDOC, ORDERPOSITION where ORDERDOC.id = ORDERPOSITION.orderId --some other conditions; Execution plan looks like this: 0 SELECT ...
0
votes
4answers
132 views

Can migration from MS Access to SQL Server or … make database faster? [closed]

A company asked me to migrate their database from MS Access to SQL Server or MySQL because they think that on those engines their database will run faster. But I wonder if their problem isn't because ...
0
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1answer
352 views

statistics State in MySQL Processlist

I have a busy MySQL Server having query SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION ...
0
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1answer
72 views

Is it possible to optimize this query? Or any recommendations to speed it up?

After looking at my mysql slow log file I see that almost every entry there is related to this query: SELECT n.nid AS nid, AVG(v.value) AS rating FROM node n LEFT OUTER JOIN votingapi_vote ...
3
votes
2answers
120 views

Should I add multiple secondary indexes to search

I have a search screen on my app where the users can use up to 4 parameters to search. I have written a stored procedure to facilitate the search. Select ID, FirstName, LastName, ...
1
vote
1answer
74 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 ...
1
vote
1answer
80 views

MySQL: What is the most optimized way to use datetime type field in query

I am working on optimization of some slow queries in my application. I found a query in which datetime comparison has been used. Below is the subquery: select * from jos_content c where c.visible = 1 ...
1
vote
1answer
337 views

Query State hangs on sending data

For some reason, the query state hangs on "Sending Data" (using show processlist;) and I have no idea why. This is the table creating script: CREATE TABLE IF NOT EXISTS `esp_game` ( `gameID` ...
1
vote
1answer
113 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 ...
1
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0answers
40 views

join performance, index vs. index+foreignkey

I'm using an orm framework that handles data (and its integrity) on top of mysql. So far I ignored foreign keys because the orm handles that just fine. I recently read that foreign keys can enhance ...
0
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2answers
141 views

MySQL: why assign NULL as default value

When we define a table, multiple times we assign default value of a column as NULL. I have How NULL is different than empty value('') as well as 0? Is there any impact of NULL value in query ...
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0answers
111 views

MySQL: how to determine key_len and its role in performance improvement of a query

I have a query, below is the structure of the table: CREATE TABLE `jos_tag_rules_fields` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(255) NOT NULL DEFAULT '', `label` varchar(255) ...
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votes
1answer
70 views

Maximum dataset size for a well-performing SQL Server 2012? [closed]

We're planning a project using SQL Server 2012 for storing about a billion records over less than 50 fields. Assuming good hardware, is SQL Server up to that task? Roughly how many request/second can ...
0
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0answers
47 views

MySQL, query optimization with join on huge table

I'm trying to execute a query on MySQL (Database created from a GTFS schema) I have two tables like these: trips trip_id | route_id --------------------- 1 | 409 2 | 409 3 ...