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

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3
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4answers
137 views

Are we a good fit for SQL Server Enterprise and table partitioning?

We currently have a production database that contains millions of records (14 million in the largest table). One function of the database is to provide time sheet information so a single table could ...
3
votes
2answers
436 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 ...
3
votes
2answers
234 views

which one is more efficient query?

I have a table called STUDENT +-----------+-----------+-----------+---------------+ | StudentID | FirstName | LastName | EnrollmenDate | +-----------+-----------+-----------+---------------+ | ...
3
votes
1answer
135 views

Why does SqlSentry Plan Explorer not give the duration of my queries?

I have a large nasty stored procedure in a 13gig database that takes 45 minutes to run when I include the actual execution plan. I save the query plan from SSMS and open in up in SQL Sentry Plan ...
3
votes
3answers
492 views

optimizing a compare query

Suppose I have two tables, A and B, and I know that size(A) = size(B). I want to confirm that the data in both tables is the same in three given columns, suppose they are X, Y, and Z (there are no ...
3
votes
2answers
843 views

How does compound index help speed up query?

Say we have a bunch of column in mysql table. Latitude Longitude Say we make an index (Latitude and Longitude) Well, the index will sort by Latitude first and IF the Latitude is the same it'll sort ...
3
votes
3answers
135 views

How can I improve this query?

About a year back I introduced a query which returns a sort of "Customers Also Purchased" data-set. At the time it ran reasonably fast however, as of late it's become very slow, sometimes taking up to ...
3
votes
2answers
257 views

How do I count rows with two properties in one index scan in SQL?

I have a table Units where I have rows ItemId, ItemCreationDate, ItemUnitsCount. ItemId is a primary key and I have a clustered index over it. I need to output the following: for each day I need to ...
3
votes
2answers
243 views

Efficiently query MAX over multiple ranges

When performing a MIN() or MAX() over a single range covered by an appropriately sorted index, SQL Server does a TOP() and so returns the value after fetching just one row. When the search criteria ...
3
votes
3answers
1k views

MySQL optimization - year column grouping - using temporary table, filesort

I have a transactions table which is having 600,000 records, I need to list the count for the dashboard on financial year basis. The table used is MyISAM. I tried adding index for the transaction date ...
3
votes
1answer
645 views

Query taking long on table with low record count

I have an Oracle flat table that grew to just below 800MB. The table was truncated and new records are being inserted. Currently there are <40 records in the table but a select * takes >30secs. ...
3
votes
5answers
451 views

Query optimization [Oracle]

The Query: select JOIN_RESULT.batch_id as BATCH_ID, JOIN_RESULT.unique_doc_id as DOCUMENT_ID, JOIN_RESULT.brand as BRAND, JOIN_RESULT.message_date_time as UPLOAD_DATE, ...
3
votes
4answers
1k views

Optimize Query with Derived Table

I have the following query select ps.id, ps.title , IFNULL(s.likes,0) as num_likes , IFNULL(s.comments,0) as num_comments , IFNULL(s.ratings,0) as num_ratings , IFNULL(s.views,0) as num_views , ...
3
votes
2answers
1k views

High CXPACKET and LATCH_EX waits

I am having some performance issues with a data processing system which I am working on. I have gathered wait stats from a one hour peroid which show a large amount of CXPACKET and LATCH_EX wait ...
3
votes
1answer
290 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 ...
3
votes
2answers
180 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, ...
3
votes
3answers
820 views

Speed up search across multiple columns

We have a table: user_info (user_id,domain_id,first_name,middle_name,last_name,work_place,.,.,.) Now, we have a user search that search across three columns first_name,last_name and work_place. ...
3
votes
1answer
522 views

Can you have a WHERE clause with a greater than operator on a composite key?

I'm a web developer (not DB admin!) having performance problems processing a 1.7m record table on MySQL. Here is that table : CREATE TABLE `bbcmapimp_pc_raw` ( `postcode` char(8) NOT NULL, ...
3
votes
1answer
76 views

Sargable Queries

Very simple question I hope, I'm currently having some scripts I inherited into my project reviewed by the database admins. This has never been done before apparently and lots of issues are being ...
3
votes
1answer
221 views

MySQL queries are 10 to 100 times slower after OS reboot

I have a MySQL server running on Ubuntu. If I restart the MySQL, everything is fine. If I however restart the OS, my queries take anywhere from 10 times to 100 times as long. The only "solution" to ...
3
votes
1answer
69 views

Every query plan statistic says my query should be faster, but it is not

I have a bit of a odd situation. I have two queries that produce the same result, according to SSMS and SQL Sentry Plan Explorer the first query should cost 95% and the 2nd query should cost 5%. ...
3
votes
1answer
1k views

Comparing two queries in SQL Server 2012

I am comparing two queries in SQL Server 2012. The goal is to use all of the pertinent information available from the query optimizer when choosing the best query. Both queries produce the same ...
3
votes
1answer
225 views

SQL Server WHERE clause on CLR method (spatial) peformance

I have a query that joins to a table containing 2 million rows and need to filter on its geometry column by its geometry type (using geom.STGeometryType()). The query takes less than a second to run ...
3
votes
2answers
4k views

SQL SERVER - Linked Server and query performance

I have a performance problem related to SQL Server/linked servers/views. I hope you can help me understand what is the best way to do what I want =). I have a database K with 3 linked servers ...
3
votes
1answer
317 views

Query Performance Issue

I have this below query which is behaving bit weird . well Weird in the sense that I couldn't find complete explanation for this. Version : Sql Server 2008 R2 Enterprise No fragmentation . ...
3
votes
1answer
5k views

MySQL: Optimize UNION with “ORDER BY” in inner queries

I just set up a logging system which consists of multiple tables with the same layout. There is one table for each data source. For the log viewer, I want to UNION all the log tables, filter them ...
3
votes
2answers
244 views

Do MySQL sub-queries essentially use as much overhead as separate queries?

If I have a query like this: SELECT name FROM ( SELECT * FROM `table` WHERE id IN (1,40,300) ORDER BY AnotherColumn ) From a bandwidth and overhead standpoint, is that the same thing as doing ...
3
votes
1answer
210 views

Get profiles values where message.sender_user_id = profile.user_id

I have this tables: default_messages CREATE TABLE IF NOT EXISTS `default_messages` ( `id` int(11) NOT NULL AUTO_INCREMENT, `subject` varchar(150) COLLATE utf8_unicode_ci NOT NULL, `message` text ...
3
votes
2answers
2k views

Copy huge amount from 1 table to other

I have two tables with same structure I need to copy over all tables from table A to table B, the problem is that some records from table A already exist in table B so that made the Import Fail. So I ...
3
votes
3answers
174 views

Nested table as condition prevents using index

The following query joining a subquery does a TABLE ACCESS FULL when the master-table uses nested table as condition. When the condition is a simple =, the same query does an INDEX RANGE SCAN as ...
3
votes
1answer
80 views

How do I deal with query getting slower when a select parameter is not specified inline?

I faced this problem twice with SQL Azure and two different queries so far. Something like this: select top(100) * from SomeView WHERE AccountId='actual-guid-typed-in-here' runs super fast but ...
3
votes
1answer
186 views

Most efficient queries on flags in TSQL: bit field or table join?

Looking for the most efficient database structure for selecting rows from a large table based on one or more true/false values. For example, whether or not a user has opted in to marketing ...
3
votes
1answer
186 views

Optimizing complex join predicates [closed]

Table Definitions CREATE TABLE [dbo].[Pin_Mtg] ( [MtgId] bigint NULL, [CntyCd] char(5) NOT NULL, [BatchDt] int NOT NULL, [BatchSeq] int NOT NULL, [MtgSeq] tinyint NOT NULL, ...
3
votes
3answers
321 views

Why does the query cost change so much and how to prevent it

The query causing me the issue is too big, but the piece that seems to be the core is quite simple, I will try to go with that: The query has an structure like: SELECT ... a lot of stuff ... ...
3
votes
2answers
246 views

Sudden Query Performance Degradation On A Linked Server

I have an application that uses a view on a SQL Server 2008 R2 instance. This view actually queries a linked server (SQL Server 2008) that has replicated data from our main ERP database. Yesterday, we ...
3
votes
1answer
856 views

MYSQL Slow SELECT with multiple joins and ORDER BY

I have this query SELECT r0_.id AS id0, r0_.deleted_at AS deleted_at1, r0_.updated_at AS updated_at2, r0_.created_at AS created_at3, r0_.is_vehicle_offer AS is_vehicle_offer4, ...
3
votes
4answers
670 views

Help with Query. Finding records that have the same relationships (MySQL)

I have a table of Listings that has a many to many relationship with a Taxons table. The table structure looks like this: listings ---------------- id (int) name (varchar) listings_taxons ...
3
votes
1answer
372 views

Need help with long running query

UPDATE: Adding a clustered index to each work table covering all fields reduced the query run times to su-bsecond. I consider this question closed. Thanks for taking the time to read this post - ...
3
votes
2answers
72 views

Looking for a possible multi-column index

I have a table highscore containing the columns: game (text) date (timestamp) score (integer) more irrelevant ones... The query most often run on it is: SELECT * FROM highscore WHERE game = ...
3
votes
1answer
637 views

MySQL Handler_read_rnd_next == tablescans without indexes?

I am in the process of tuning our Percona 5.5 server, and have been using percona's tools to plot our database's performance. In the MySQL Handlers Plot, i have been noticing alot of ...
3
votes
1answer
762 views

MySQL 5.5.8 InnoDB Foreign Key, JOIN performance

We are using aws/rds, MySQL 5.5.8. all InnoDB. For performance purposes, we have merged some data-elements into varchar fields; mini-sized int and date type fields; added covering indexes; ...
3
votes
1answer
478 views

Measuring the relative performance of queries given the assertion that “cost” isn't reliable

The cost field is a comparative cost that is used internally to determine the best cost for particular plans. The costs of different statements are not really directly comparable. Source Does ...
3
votes
1answer
135 views

How to search for an ID and its descendants in this query?

I have the following tables: Project Unit ------------- --------------- ID | IDUnit ID | IdParent I have to select all projects that have the IDUnit ...
3
votes
1answer
519 views

Oracle: How to gather stats in a logical standby database?

I have a Primary and a (logical) Standby Database. The Schema 'APP' gets synced. Now a User has performance issues running a query against some tables in this 'APP' schema of the Standby Database. On ...
3
votes
3answers
850 views

PostgreSQL 8.3: Slow GROUP BY on large table

I have a table with about 10 million records. I want to do a simple group by, but it's using a sequential scan and is slow... select run_id, count(*) from result group by run_id; I have an index ...
3
votes
2answers
162 views

Query planner thinks doing a sequential scan on a very large table is faster than using an index?

I've got a query that selects the most favorited photo for each of the last 12 editions for a particular domain (this is just a segment of a larger query, but the problem seems to stem from here): ...
2
votes
2answers
206 views

DISTINCT not using an index [duplicate]

I have table (2139868 rows): COLUMN1 NUMBER(20,0) COLUMN2 XMLTYPE COLUMN3 XMLTYPE COLUMN4 VARCHAR2(50 BYTE) COLUMN5 VARCHAR2(50 BYTE) COLUMN6 VARCHAR2(50 BYTE) COLUMN7 VARCHAR2(50 BYTE) COLUMN8 ...
2
votes
4answers
976 views

Remove sub-string from WHERE clause

I have a stored procedure that is using the SUBSTRING function in the WHERE clause. SELECT DISTINCT ColumnBB, ColumnCC FROM TableAA WITH (NOLOCK) WHERE SUBSTRING(ColumnAA, 1, 17) = @VariableA; ...
2
votes
3answers
246 views

selecting multiple instances of a record based on record lifespan over years

I have a table of items that have a origin date and a life span. I want to create a procedure that selects all of the items that will need to be replaced in a specific duration. I feel like there is a ...
2
votes
2answers
151 views

What can be done to further enhance performance of Multiple Join and Aggregate Queries?

I have a typical star schema simulated here, and I am mentioning two queries: first query simply joins the fact table with 2 dimension tables and 1 calendar table, and the second query joins and ...