All Questions
12 questions
0
votes
2
answers
857
views
MySQL multiple subqueries - slow ordering
Any idea how to optimise this query?
It runs very slow when using the ORDER BY (~10 seconds) clause. If I remove the order_by clause, then it executes for milliseconds.
Problem is, that I need to been ...
0
votes
1
answer
651
views
Ordering by field, constructed by subquery is slow
My tables (oversimplified for clarity):
documents: registrations:
|id| |id|document_id|date|
My simplified query:
SELECT *
FROM (SELECT documents.*,
(SELECT max(date)
...
0
votes
0
answers
45
views
Postresql using subquery select in order by clause
Is it possible to order by a selected columnname?
SELECT * FROM tablex ORDER BY quote_ident((
select column_name from information_schema.columns
where table_name = tablex AND column_name LIKE '...
- 53
-4
votes
1
answer
354
views
Selecting data from a sub query
I am doing the exercises this is the link (https://www.wiseowl.co.uk/sql/exercises/standard/subqueries/4228/).
Can anyone help me. Thanks in advance!
Question
Write a SELECT statement to return events ...
11
votes
2
answers
15k
views
How to combine ORDER BY and LIMIT with an aggregate function?
Here is a fiddle for my question.
I have a simple table layout:
class
person: belongs to a class
I want to select all classes, and for each class, I want the first two person identifiers of the ...
- 455
1
vote
2
answers
130
views
How to sort records before inter-row calculation?
I have a time sequence data set to analyze but the difficulty is that
the data set is very big.
the time sequence events are committed by different objects with affiliation.
its in mysql, there is no ...
- 169
5
votes
1
answer
3k
views
Subquery ORDER BY doesn't work on MySQL 5.6, but works on 5.5
I try to join 3 tables (products, prices, categories) together to get a result of latest & lowest prices from the joined tables.
I was able to get the expected result on MySQL 5.5, but after ...
- 51
3
votes
1
answer
3k
views
MySQL Update a table based on the last data from another table while grouping with conditions
I need a query to UPDATE a series of fields based on another table
Table lp_plates_backup
| uid | brand | model |
| 1 | | |
| a | Old | Error |
|...
- 45
3
votes
1
answer
1k
views
MySQL: Why queries with subqueries are much faster than single query?
I made few queries on my db lately
First query:
SELECT `table`.*
FROM (`table`)
WHERE table.id in(27172172,[...bunch of ids...],27171770)
ORDER BY field (`table`.`id`, 27172172,27172168,[......
- 41
2
votes
1
answer
15k
views
GROUP_CONCAT with ORDER BY , but results are not ordered
The following query works fine
SELECT
*,
(SELECT
GROUP_CONCAT(url SEPARATOR '$$' )
FROM project_photos
WHERE project_id = projects.id
ORDER BY priority) AS images
FROM projects
WHERE catID = 2
LIMIT ...
- 356
11
votes
1
answer
28k
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 ...
- 213
2
votes
2
answers
1k
views
Order by sub select
I have 3 tables: articles, paragraphs, notes
An article may have many paragraphs, and a paragraph may have 0 or 1 note.
Now I want to find all notes belong to an article:
select * from notes
where ...
- 325