I have a table organized in the following way:
id | userid | action | notes | created_at
-----------------------------------------
1 | 1 | foo | bar | datetime
2 | 33 | foo | bax | datetime
3 | 1 | foo | okay | datetime
4 | 3 | bam | bad | datetime
5 | 33 | foo | bom | datetime
What I would like to be able to do is, in Ruby on Rails, group the rows by userid but grab only the most recent entry for each group.
As it stands, I've gotten this far:
Thing.select("userid, notes").where(:action => "foo").order('`when` DESC')
Which will usually return something like:
userid | notes
--------------
1 | bar
33 | bax
When what I'm looking for is this:
userid | notes
--------------
1 | okay
33 | bom
I think I copy/pasted that all right...heh. Is there a way to achieve what I'm trying to do? Without resorting to searching inside my app itself? Thanks.
Update Attempted the first suggestion, no dice.
Just add .order("id desc") to the end of your line
Related
I've recently tried to create an executable with python 2.7 which can read a MySQL database.
The database (named 'montre') regroups two tables : patient and proto_1
Here is the content of those tables :
mysql> select * from proto_1;
+----+------------+---------------------+-------------+-------------------+-----
----------+----------+
| id | Nom_Montre | Date_Heure | Temperature | Pulsion_cardiaque | Taux
_oxy_sang | Humidite |
+----+------------+---------------------+-------------+-------------------+-----
----------+----------+
| 1 | montre_1 | 2017-11-27 19:33:25 | 22.30 | NULL |
NULL | NULL |
| 2 | montre_1 | 2017-11-27 19:45:12 | 22.52 | NULL |
NULL | NULL |
+----+------------+---------------------+-------------+-------------------+-----
----------+----------+
mysql> select * from patient;
+----+-----------+--------+------+------+---------------------+------------+----
----------+
| id | nom | prenom | sexe | age | date_naissance | Nom_Montre | com
mentaires |
+----+-----------+--------+------+------+---------------------+------------+----
----------+
| 2 | RICHEMONT | Robert | M | 37 | 1980-04-05 23:43:00 | montre_3 | ess
aye2 |
| 3 | PIERRET | Mandy | F | 22 | 1995-04-05 10:43:00 | montre_4 | ess
aye3 |
| 14 | PIEKARZ | Allan | M | 22 | 1995-06-01 10:32:56 | montre_1 | Hea
lthy man |
+----+-----------+--------+------+------+---------------------+------------+----
----------+
As I'm just used to code in C (no OOP), I didn't create class in the python project (shame on me...). But I managed, in two files, to create something (with mysql.connector) which can print (on the cmd) my database and excecute sub like looking-for() etc.
Now, I want to create a GUI for users with pyqt. Unfortunately, I saw that the structure is totally different, with class etc. But okay, I tried to go throught this and I've created a GUI which allows to display the table "patient". But I didn't manage (in the datasheet of QT) to find how I can use the programs I've already created to display. Neither how to display in a tableWidget only several rows of my table patient for exemple (Using QSQL).
For example, if I want to display all the table patient, I use this line (pyQt):
self.model.setTable("patient")
For this one, I got it, but that disturb me because there is no MySQL coding requisites to display my table and so I don't know how to sort only the rows we want to see and display them. If we only want to see, for example, the ID n°2, how to display in the table:widget only Robert ?
To recap, I want to know :
If I can take the coding I've created and combine it with pyQT
How to display (tableWidget) only rows which are selected by MySQL. Is that possible ?
Please find in the URL my code for a better understanding of my problem :
https://drive.google.com/file/d/1nxufjJfF17P5hN__CBEcvrbuHF-23aHN/view?usp=sharing
I hope I was clear, thank you all for your help !
I want to select value from table sorted by a certain order.
I have a table called test that looks like this:
| date | code | value |
+----------+-----------+----------+
| 20050104 | 000005.SZ | -6359.19 |
| 20050104 | 600601.SH | -7876.34 |
| 20050104 | 600602.SH | -25693.3 |
| 20050104 | 600651.SH | NULL |
| 20050104 | 600652.SH | -15309.9 |
...
| 20050105 | 000005.SZ | -4276.28 |
| 20050105 | 600601.SH | -3214.56 |
...
| 20170405 | 000005.SZ | 23978.13 |
| 20170405 | 600601.SH | 32212.54 |
Right now I want to select only one date, say date = 20050104, and then sort the data by a certain order (the order that each stock was listed in the stock market).
I have another table called stock_code which stores the correct order:
+---------+-----------+
| code_id | code |
+---------+-----------+
| 1 | 000002.SZ |
| 2 | 000004.SZ |
| 3 | 600656.SH |
| 4 | 600651.SH |
| 5 | 600652.SH |
| 6 | 600653.SH |
| 7 | 600654.SH |
| 8 | 600602.SH |
| 9 | 600601.SH |
| 10 | 000005.SZ |
...
I want to sorted the selected data by stock_code(code_id), but I don't want to use join because it takes too much time. Any thoughts?
I tried to use field but it gives me an error, please tell me how to correct it or give me an even better idea.
select * from test
where date = 20050104 and code in (select code from stock_code order by code)
order by field(code, (select code from stock_code order by code));
Error Code: 1242. Subquery returns more than 1 row
You told us that you don't want to join because it takes too much time, but the following join query is probably the best option here:
SELECT t.*
FROM test t
INNER JOIN stock_code sc
ON t.code = sc.code
WHERE t.date = '20050104'
ORDER BY sc.code_id
If this really runs slowly, then you should check to make sure you have indices setup on the appropriate columns. In this case, indices on the code columns from both tables as well as an index on test.date should be very helpful.
ALTER TABLE test ADD INDEX code_idx (code)
ALTER TABLE test ADD INDEX date_idx (date)
ALTER TABLE code ADD INDEX code_idx (code)
I have table named questions like follows
+----+---------------------------------------------------------+----------+
| id | title | category |
+----+---------------------------------------------------------+----------+
| 89 | Tinker or work with your hands? | 2 |
| 54 | Sketch, draw, paint? | 3 |
| 53 | Express yourself clearly? | 4 |
| 77 | Keep accurate records? | 6 |
| 32 | Efficient? | 6 |
| 52 | Make original crafts, dinners, school or work projects? | 3 |
| 70 | Be elected to office or make your opinions heard? | 5 |
| 78 | Take photographs? | 3 |
| 84 | Start your own political campaign? | 5 |
| 9 | Free spirit or a rebel? | 3 |
| 38 | Lead a group? | 5 |
| 71 | Work in groups? | 4 |
| 2 | Helpful? | 4 |
| 4 | Mechanical? | 6 |
| 14 | Responsible? | 6 |
| 66 | Pitch a tent, an idea? | 1 |
| 62 | Write useful business letters? | 5 |
| 28 | Creative? | 3 |
| 68 | Perform experiments? | 2 |
| 10 | Like to figure things out? | 2 |
+----+---------------------------------------------------------+----------+
I have a sql query to get one random record from each category.Can any one convert the mysql query to rails activerecord query(with out using Question.find_by_sql).This mysql query is working absolutely fine but I need only active record query because of my dependency in further steps.
Here is mysql query
SELECT t.id, title as question, category
FROM
(
SELECT
(
SELECT id
FROM questions
WHERE category = t.category
ORDER BY RAND()
LIMIT 1
) id
FROM questions t
GROUP BY category
) q JOIN questions t
ON q.id = t.id
Thank You for your consideration!
When things get crazy one have to reach out for Arel:
It is intended to be a framework framework; that is, you can build
your own ORM with it, focusing on innovative object and collection
modeling as opposed to database compatibility and query generation.
So what we want to do is to let Arel create the query for us. Moreover the approach here is gonna be used: the questions table is left joined with randomized version of itself:
q_normal = Arel::Table.new("questions")
q_random = Arel::Table.new("questions").project(Arel.sql("*")).order("RAND()").as("q2")
Time to left join
query = q_normal.join(q_random, Arel::Nodes::OuterJoin).on(q_normal[:category].eq(q_random[:category])).group(q_normal[:category]).order(q_random[:category])
Now you can use which columns you want using project, e.g.:
query.project(q_normal[:id])
The only way I can think of to do this requires a good bit of application code. I don't think there's a way of accessing the RAND() functionality in MySQL (or equivalent in other DB technologies) using ActiveRecord. Here's what I came up with:
counts = Question.group(:category_id).count(:id)
offsets = {}
counts.each do |cat_id, count|
offsets[cat_id] = rand(count)
end
random_questions = []
offsets.each do |cat_id, offset|
random_questions.push(Question.where(:category_id => cat_id).offset(offset).first)
end
I have the following situation:
Table Words:
| ID | WORD |
|----|--------|
| 1 | us |
| 2 | to |
| 3 | belong |
| 4 | are |
| 5 | base |
| 6 | your |
| 7 | all |
| 8 | is |
| 9 | yours |
Table Sentence:
| ID | SENTENCE |
|----|-------------------------------------------|
| 1 | <<7>> <<6>> <<5>> <<4>> <<3>> <<2>> <<1>> |
| 2 | <<7>> <<8>> <<9>> |
And i want to replace the <<(\d)>> with the equivalent word from the Word-Table.
So the result should be
| ID | SENTENCE |
|----|--------------------------------|
| 1 | all your base are belong to us |
| 2 | all is yours |
What i came up with is the following SQL-Code:
SELECT id, GROUP_CONCAT(word ORDER BY pos SEPARATOR ' ') AS sentence FROM (
SELECT sentence.id, words.word, LOCATE(words.id, sentence.sentence) AS pos
FROM sentence
LEFT JOIN words
ON (sentence.sentence REGEXP CONCAT('<<',words.id,'>>'))
) AS TEMP
GROUP BY id
I made a sqlfiddle for this:
http://sqlfiddle.com/#!2/634b8/4
The code basically is working, but i'd like to ask you pros if there is a way without a derived table or without filesort in the execution plan.
You should make a table with one entry per word, so your sentense (sic) can be made by joining on that table. It would look something like this
SentenceId, wordId, location
2, 7, 1
2, 8, 2
2, 9, 3
They way you have it set up, you are not taking advantage of your database, basically putting several points of data in 1 table-field.
The location field (it is tempting to call it "order", but as this is an SQL keyword, don't do it, you'll hate yourself) can be used to 'sort' the sentence.
(and you might want to rename sentense to sentence?)
Some background: an 'image' is part of one 'photoshoot', and may be a part of zero or many 'galleries'. My tables:
'shoots' table:
+----+--------------+
| id | name |
+----+--------------+
| 1 | Test shoot |
| 2 | Another test |
| 3 | Final test |
+----+--------------+
'images' table:
+----+-------------------+------------------+
| id | original_filename | storage_location |
+----+-------------------+------------------+
| 1 | test.jpg | store/test.jpg |
| 2 | test.jpg | store/test.jpg |
| 3 | test.jpg | store/test.jpg |
+----+-------------------+------------------+
'shoot_images' table:
+----------+----------+
| shoot_id | image_id |
+----------+----------+
| 1 | 1 |
| 1 | 2 |
| 3 | 3 |
+----------+----------+
'gallery_images' table:
+------------+----------+
| gallery_id | image_id |
+------------+----------+
| 1 | 1 |
| 1 | 2 |
| 2 | 3 |
| 3 | 1 |
| 4 | 1 |
+------------+----------+
What I'd like to get back, so I can say 'For this photoshoot, there are X images in total, and these images are featured in Y galleries:
+----+--------------+-------------+---------------+
| id | name | image_count | gallery_count |
+----+--------------+-------------+---------------+
| 3 | Final test | 1 | 1 |
| 2 | Another test | 0 | 0 |
| 1 | Test shoot | 2 | 4 |
+----+--------------+-------------+---------------+
I'm currently trying the SQL below, which appears to work correctly but only ever returns one row. I can't work out why this is happening. Curiously, the below also returns a row even when 'shoots' is empty.
SELECT shoots.id,
shoots.name,
COUNT(DISTINCT shoot_images.image_id) AS image_count,
COUNT(DISTINCT gallery_images.gallery_id) AS gallery_count
FROM shoots
LEFT JOIN shoot_images ON shoots.id=shoot_images.shoot_id
LEFT JOIN gallery_images ON shoot_images.image_id=gallery_images.image_id
ORDER BY shoots.id DESC
Thanks for taking the time to look at this :)
You are missing the GROUP BY clause:
SELECT
shoots.id,
shoots.name,
COUNT(DISTINCT shoot_images.image_id) AS image_count,
COUNT(DISTINCT gallery_images.gallery_id) AS gallery_count
FROM shoots
LEFT JOIN shoot_images ON shoots.id=shoot_images.shoot_id
LEFT JOIN gallery_images ON shoot_images.image_id=gallery_images.image_id
GROUP BY 1, 2 -- Added this line
ORDER BY shoots.id DESC
Note: The SQL standard allows GROUP BY to be given either column names or column numbers, so GROUP BY 1, 2 is equivalent to GROUP BY shoots.id, shoots.name in this case. There are many who consider this "bad coding practice" and advocate always using the column names, but I find it makes the code a lot more readable and maintainable and I've been writing SQL since before many users on this site were born, and it's never cause me a problem using this syntax.
FYI, the reason you were getting one row before, and not getting and error, is that in mysql, unlike any other database I know, you are allowed to omit the group by clause when using aggregating functions. In such cases, instead of throwing a syntax exception, mysql returns the first row for each unique combination of non-aggregate columns.
Although at first this may seem abhorrent to SQL purists, it can be incredibly handy!
You should look into the MySQL function group by.