A class of issues where a database executes a query inefficiently due to the optimiser selecting an innapropriate query plan.
7
votes
3answers
481 views
Can spatial index help a “range - order by - limit” query
Asking this question, specifically for Postgres, as it has good supoort for R-tree/spatial indexes.
We have the following table with a tree structure (Nested Set model) of words and their ...
9
votes
1answer
685 views
SQL query for combinations without repetition
I need a query which can be used in (or as) a function and retrieves all combinations of n values. And I need all combinations of length k where k = 1..n.
Extended sample input and result so input ...
5
votes
2answers
4k views
Learning to Optimize SQL Queries and Understand Execution Plans - Resources?
I find myself writing more and more SQL queries at work (mostly Oracle 11g, but some SQL Server 2005-2008) and have started creating some pretty complex views for the rest of the analyst team.
They ...
4
votes
1answer
179 views
How to Optimise Query
I have a database structure similar to this,
CREATE TABLE [dbo].[Dispatch](
[DispatchId] [int] NOT NULL,
[ContractId] [int] NOT NULL,
[DispatchDescription] [nvarchar](50) NOT NULL,
...
9
votes
4answers
914 views
Is it possible to increase query performance on a narrow table with millions of rows?
I have a query that is currently taking an average of 2500ms to complete. My table is very narrow, but there are 44 million rows. What options do I have to improve performance, or is this as good as ...
4
votes
1answer
122 views
How should we handle rows which won't be queried once they are old in PostgreSQL?
We have a table in a PostgreSQL database which is growing on the order of millions of rows per day.
Each row consists of:
ID
Foreign user ID
Date and time
Other data
The date and time aren't ...
4
votes
2answers
588 views
Why does MySQL choose this execution plan?
I have two queries,
select some_other_column
from `table`
order by primary_index_column asc
limit 4000000, 10;
and
select some_other_column
from `table`
order by secondary_index_column asc
...
2
votes
5answers
264 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,
...
1
vote
1answer
145 views
Slow query performance
My database contains 20,000 rows and the following query is slow. Please help me to speed this up:
SELECT r.report_id,
r.user_id,
u.user_name,
u.user_mail,
...
1
vote
1answer
86 views
Combining columns in index
With reference to RolandoMySQLDBA's answer on
MySQL: Index when joining to tables not being used (Performance optimizing question)
He mentioned
Make sure you build an index that involves the ...
1
vote
3answers
1k views
Is it normal to use many Triggers?
I have many so-called summary columns throughout my database to count number of rows in other tables. For example, counting the number of comments by a user (a column in the user table). Currently, I ...
4
votes
3answers
369 views
Some book suggestions for performance tuning
I am in the process of improving performance on our database application. While I am not a DBA, I am pretty comfortable with SQL. I am after a book that can help me understand how queries written in ...
3
votes
3answers
238 views
Is it better to seperate a big query into multiple smaller queries?
There are situations which require to have really big query joining several tables together with sub select statements in them to produce the desired results.
My question is, should we consider using ...
2
votes
0answers
161 views
MySQL: Improve performance for one row insert into table with unique constraint
I have a table with ~ 40 mil records, with a unique index on the url collumn, of type varchar(255).
Now the insert speed is about 30/s, is this expected? how could I improve it?
I can't use bulk ...
1
vote
2answers
177 views
How do I force a JOIN to use a specific index in MySQL?
I have a query that JOINs 2 tables; lineitem and part,
select
sum(l_extendedprice* (1 - l_discount)) as revenue
from
lineitem force index for join (l_pk),
part
where
(
...
2
votes
3answers
139 views
How to get all non deleted messages from one user
I have two tables one for messages called default_messages and the other for recipients called default_recipient. This is how SQL for those table looks like:
CREATE TABLE IF NOT EXISTS ...
1
vote
1answer
103 views
Several values from different tables
I'm totally lost here and not know how to get this to work and hope any can help me here. I have several tables: default_users, default_profiles, default_status, default_comment and latest ...
1
vote
0answers
86 views
Get all comment.message, status.message, users.* and profiles.* where users.user_id exists in friend.friend_id or friend.user_id
I need some help building this query because it's a bit complicated at least for me. I need to get all comment.message, status.message, users.* and profiles.* where users.user_id exists in ...
0
votes
2answers
171 views
optimize big sql query
My query has to return a statistics for example for march containing productname and price and its sidedishes (1:n relation) with the right price of each sidedish and the right tax for each sidedish ...
0
votes
2answers
136 views
MySQL: can not get rid of “Using filesort” in a simple query
Simple query but can not get rid of "using filesort":
CREATE TABLE IF NOT EXISTS `online` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`uid` int(11) NOT NULL,
`expiration` int(11) NOT NULL,
...
