In the context of a database, optimisation refers to the process of the query optimiser selecting an efficient physical execution plan.

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Multiple WHERE IN on multiple columns

I am not very experienced with sql queries and looking for an efficient way to perform the same WHERE IN condition on multiple columns. More specifically, i'm doing the following: SELECT a, b FROM ...
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2answers
1k views

nvarchar(max) converting to varchar and table optimization

I am working with a table that has all character types set to nvarchar some of them are nvarchar(max). We are converting all these to varchar and specifying a character width based upon the actual ...
8
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1answer
161 views

Overcome MERGE JOIN(INDEX SCAN) with explicit single KEY value on a FOREIGN KEY

Added 7/11 The issue is deadlocks occur because of index scan during MERGE JOIN. In this case a transaction trying to get S lock on the whole index at the FK parent table, but previously another ...
3
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1answer
76 views

MySQL Filesort/Order By Slow

I've been struggling with a query for the past few weeks and it now just appears as gobbly-gook to me when I try to optimize. The query runs - at about 2.3 seconds, but I know there has to be a more ...
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1answer
2k views

How to partition existing table in postgres?

I would like to partition a table with 1M+ rows by date range. How is this commonly done without requiring much downtime or risking losing data? Here are the strategies I am considering, but open to ...
5
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1answer
105 views

Postgres: Is migrating old records to separate table and creating new aggregated records a good strategy to improve search speed?

I have a table with 1M+ records. New records are created and updated each day each time an event occurs for each type of event (which there are many). I frequently need to find sums across many ...
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0answers
30 views

Optimization for query n increase performance

I am executing the following query: select count(inspection_result) from table where (inspection_time between "2015-06-28" and "2015-07-04") and inspection_result= 1 and part_type = "39000048" and ...
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1answer
91 views

Dynamic Partition Elimination when using “OR ” or “IN”

Say I have a query like this: SET @ContainerId = 5 SELECT * FROM Container.Container_Partitioned WHERE containerId = @ContainerId When I run this, I get a query plan with Actual Partition ...
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2answers
291 views

How can i update my database from another database using temporary tables?

I want to update tables of my database using another big database every day with using temporary tables and without returning result. How can i update it? This my temporary table : use data_pro; ...
3
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0answers
94 views

Why the stored procedure is much slower than a temporary table? [closed]

I want to do the updating of my database every day and I will like to use stored procedures but the time of execution of the temporary table is faster than the stored procedure. How can I optimize my ...
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0answers
157 views

How can i add index in MYSQL stored procedure?

I can not use alter table () on my stored procedure i don't have a permission to do that in the big database data_pro. How can i use index in my stored procedure for my 2 fields in where condition? ...
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2answers
193 views

SQL Server 2008 R2 Memory Pressure

My SQL Server has a weird problem. It seems it happens with the same matter. It always restarts after running a period of time(about one month long). And I used dbcc memorystatus to check the problem. ...
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1answer
250 views

Why is my stored procedure very much slower than the same MYSQL query? [duplicate]

My stored procedure is very slow compared to a normal query or a temporary table. How can I optimize my stored procedure? CREATE DEFINER=`datasll`@`...` PROCEDURE `product`() BEGIN EXPLAIN ...
12
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1answer
342 views

Why does referencing a variable in a join predicate force nested loops?

I came across this issue recently and couldn't find any discussion of it online. The query below DECLARE @S VARCHAR(1) = ''; WITH T AS (SELECT name + @S AS name2, * ...
9
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2answers
159 views

Why isn't the primary (clustered) key being used in this query?

I have a SQL Server 2008 R2 table whose schema structure looks as follows: CREATE TABLE [dbo].[CDSIM_BE] ( [ID] [bigint] NOT NULL, [EquipmentID] [varchar](50) NOT NULL, [SerialNumber] ...
3
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1answer
93 views

Improve performance on SQL Server Query

I'm trying to increase the performance of a query and I'm out of ideas: The query does this: gets a 'Process' with specific priorities on selection namely: Picks up a process that has been waiting ...
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0answers
76 views

Need your help in query tuning

I read ​one article which shows how to use different aggregations effectively. http://sqlblog.com/blogs/paul_white/archive/2011/12/04/is-distinct-aggregation-still-considered-harmful.aspx I am ...
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1answer
86 views

Select last row for a certain group

I have two tables: Table users columns | type | notes --------|--------|------- id | bigint | PK ... | ... | ... Table events columns | type | notes ...
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0answers
227 views

Why my sql query run faster than my stored procedure?

I am trying to write a script in MYSQL Workbench to update my database every day using stored procedure but I find it too slow compared normal query or temporary tables. If i use temporary table the ...
3
votes
1answer
670 views

Mongodb high lock percentage / slow queries

I'm working with an application using MongoDB that is getting a fairly large number of incoming requests and I've noticed that the responses are getting slower as the number of requests get higher. ...
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2answers
81 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 ...
2
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1answer
81 views

How to optimize this MySQL query?

Hi can someone help me to optimize this MySQL query, it's taking very long to complete, I have set indexes correctly, but it seems that string operations are slowing this query SELECT ...
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2answers
67 views

Is LIMIT processed before or after retrieving data?

MySQL. My heavy query crashed our MySQL server. If I add LIMIT 10 will it make my query more lightweight? (both for indexed and unindexed queries). Which way LIMIT are processed: before the rest of ...
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3answers
235 views

Optimizing a query which runs through all hours in a day

I need help optimizing a query. I'm using PostgreSQL 9.3.4 currently but can upgrade to 9.4 if needed. I have a table with 60+ millions of records which looks like this: ...
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0answers
34 views

Optimize query with access to tiny fraction of data

I am trying to optimize some queries but I can only use a tiny portion of the actual data they will be executed against later. Probably the query optimizer will generate completely different plans ...
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0answers
365 views

Oracle 10.2.0.4 query hundreds times slower than the same query on Oracle 10.2.0.3

I have an issue with query on Oracle 11.2.0.4.0 (it takes forever to complete and CPU is at 100% all the time) so I was trying to change optimizer_features_enable to previous versions. It worked with ...
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2answers
86 views

Optimize table by removing large field

I have a MySQL table of articles. It's growing rapidly, and over 50% of the size on disk is accounted for by the article body field, as you might expect. There are no indexes on the body, but 8/16 ...
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2answers
42 views

Which query performs better when searching a row where a column has maximum?

Consider a simple table for example purposes: person(name varchar, age int) I have a task to retrieve the oldest person. Which query is better in general for such problems? Query 1: criteria with ...
0
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1answer
32 views

optimizing mysql query using explain

I'm trying to optimize a query for a client; I'll try to describe what I'm going for at a high level before diving into the structure. The client database has a table of transactions (currently ~352k ...
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4answers
901 views

MSSQL Select all parent rows for which exists a combination of children rows with desired value

I would like to select all parent rows for which exists a combination of children rows with desired value. The easiest approach is to use multiple exists clauses, but this is not optimal - anyone ...
2
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2answers
272 views

MySQL JOIN two tables and get latest result

I want to JOIN two tables and get the latest result from each one of those two in a single table. I'm kind of concerned about speed too since tables are growing kinda fast. Close to 60-70k records a ...
1
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1answer
91 views

Optimizing a query that performs worse on a smaller dataset

I am trying to run this query. The * is just for simplification, I'm selecting ~10 specific fields for some calculations. SELECT * FROM `orders` LEFT JOIN `orders_processed` ON ...
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0answers
27 views

Filesort when using view

I am sorry for asking, but I can't figure what i am doing wrong and filesort appears in my explain. The id column that I use for sorting in the following examples is a primary key... If I create ...
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2answers
2k views

Trace Flag 4199 - Enable globally?

This may fall under the category of opinion, but I'm curious if people are using trace flag 4199 as a startup parameter for SQL Server. For those that have used it, under what circumstances did you ...
2
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2answers
457 views

Slow Performance caused by Correlated Sub-queries & Clustered Index Seek

I'm running a query in which one of the tables (FIELDDATA) has nearly 400,000 records which is taking more than 2 minutes to execute. I ran the execution plan, and noticed that the clustered seek ...
1
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1answer
94 views

Generate rows based on value in 2 columns. Bug?

I have the following table in Oracle: ID START END _ID01 AB050 AB100 _ID01 AB101 AB150 _ID02 AB0251 AB0300 _ID01 AB00301 AB00302 I want to generate as many rows and every ...
0
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2answers
277 views

Sqlite query slow whilst it should be fast

I have the following query: SELECT breakType,date,blockname,modname,metadata,nbtdata,x,y,z FROM BlocksBrokenByExplosion WHERE dimension=0 AND y>60 AND y<70 AND x>150 AND ...
0
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1answer
68 views

Having four different tables or having one table with one more field?

I have a website with 4 translation (That is Arabic with 4 different Persian translation), and I had exported each of these translations to different tables. Which one of these ways are faster and ...
6
votes
2answers
97 views

Will the Oracle optimizer still plan a join if I'm not reading any columns in the joined table?

Suppose I have the following view: CREATE VIEW dummy AS SELECT a.some_column, b.other_column FROM a LEFT JOIN b USING (key_column); When I do a SELECT some_column FROM dummy, is there a way to ...
0
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1answer
2k views

Connection problem different errors .net application

We have a SQL server with some relational databases. We have another webbserver with applications which communicate with the databases. We have an issue with one of our customers and we get some ...
0
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3answers
111 views

Adding order by to a query is slowing down the query even after Indexing

While joining columns with huge data even after indexing the column order by is slowing down the query. Without order by query is executing within 2 secs. But with order by query is taking 145 secs. ...
2
votes
2answers
986 views

SELECT and UPDATE in a single query while updating selective fields of duplicate records only

I have a MySQL table named Contacts_table with, say, the following contents: ID NUMBER NAME CITY 001 2222222222 John Doe Los Angeles 002 ...
0
votes
1answer
47 views

How to determine if an Index is uselss in Percona MySQL?

Using Percona Server 5.5 I've a table which stores user activty (lets call it user_activity). It was created quite a few years ago when I had only a little bit of knowledge about database ...
3
votes
2answers
107 views

Mysql Index for concat select

For Below Query SELECT MAX(CONCAT(date, ' ', last_entry)) AS LAST_LOG FROM entry_log WHERE TRIM(LEADING 0 FROM card_no)='2948' I've index on date card_no date,last_entry ...
4
votes
2answers
393 views

Optimizing queries on a range of timestamps (one column)

I am using Postgres 9.3 through Heroku. I have a table, "traffic", with 1M+ records that has many inserts and updates every day. I need to perform SUM operations across this table over different time ...
5
votes
1answer
143 views

Query looks optimal but logical reads is huge

I run the following (really simple) query in SQL Server: SELECT MAX(PK_Field1) FROM MainTable kh WHERE kh.PK_Field1 >= '2014-12-01T00:00:00' AND kh.PK_Field2 = 1572 AND ...
3
votes
1answer
520 views

DB2 CASE statement faster with parentheses around entire WHEN

Trying to optimize slow queries, someone on my team come across this. Having this in our stored proc: CASE WHEN MYCOL BETWEEN @STARTNUM AND @ENDNUM AND RECTYPE = 'RO' THEN 1 ELSE 0 ...
0
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1answer
57 views

Storing small array of many possibilities

Let's say I need to store the text of a series of books, line per line in a database, and present them in a (CMS-based) website. I thought the correct setup would be: a 'library' table: containing ...
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2answers
141 views

How to most efficiently store possible combinations of categories?

I have a table of categories (currently with 14 rows, not likely to change). A need to cache combinations of categories emerged, so I'm creating a table of allowed combinations (only few hundreds of ...
2
votes
2answers
233 views

MySQL taking too much CPU

Below is my .cnf file and if I see my CPU consumption 99.99% of it my the mysqld commands. The MySQL server is connected from remote machines that update data in it frequently, but I make sure that ...