I have a table called Transaction with relation User, Transaction has a field called balance.
Data looks like:
id user_id balance
1 22 365
2 22 15
3 22 900
4 32 100
4 32 50
I need all users associative data and last insert balance field of User. For example here id=3 is last inserted data for user_id=22.
In raw SQL I have tried this:
select * from transactions where id in (select max(id) from transactions group by user_id)
If I add here a inner join I know I can also retrieve User data. But how can I do this in CakePHP?
IMHO, subqueries are ugly in CakePHP 2.x. You may as well hard code the SQL statement and execute it through query(), as suggested by #AgRizzo in the comments.
However, when it comes to retrieving the last (largest, oldest, etc.) item in a group, there is a more elegant solution.
In this SQL Fiddle, I've applied the technique described in
Retrieving the last record in each group
The CakePHP 2.x equivalent would be:
$this->Transaction->contains('User');
$options['fields'] = array("User.id", "User.name", "Transaction.balance");
$options['joins'] = array(
array('table' => 'transactions',
'alias' => 'Transaction2',
'type' => 'LEFT',
'conditions' => array(
'Transaction2.user_id = Transaction2.user_id',
'Transaction.id < Transaction2.id'
)
),
);
$options['conditions'] = array("Transaction2.id IS NULL");
$transactions=$this->Transaction->find('all', $options);
Related
I'm running a query that will get results based on a location search and date. I have a geography column with location points (lat/long) that's indexed. When I search for an event on a date it searches for all events within a distance (radius) on that date.
The problem is that if there are, say 10 events, all at the same location on the same date, all 10 results will come back in the first page. I'd like to mix this up and only show 2-3 from each location to give the result set some variety, so the user doesn't just see all events from one location.
I know I can use distinct to only fetch one event from each location, but how would I use it to get me 2-3 distinct values?
Here is my query so far.
viewModel.Events = dbContext.YogaSpaceEvents
.Where(i => i.EventDateTime >= adjustedSearchDate &&
i.LocationPoints.Distance(location) <= radius)
.Distinct()
.OrderBy(i => i.EventDateTime)
.Select(i => new EventResult
{
//fill view model here
})
.ToPagedList(Page, 10);
I don't think there's a way to get EF to generate such a query, which for SQL Server would be something like this:
with q as
(
select *,
( row_number() over (partition by StateProvinceId order by CityID) -1 ) / 3 MyRanking
from Application.Cities
)
select CityId, CityName,StateProvinceID
from q
order by MyRanking, StateProvinceID, CityID
offset 10 rows
fetch next 20 rows only
Note that this example doesn't use distance. But the idea is identical: the first 3 cities in each state are returned first, then the next 3, etc.
Or you could fetch all the matching events and sort them in memory.
I think you should be able to do something like:
dbContext.YogaSpaceEvents
.Where(i => i.EventDateTime >= adjustedSearchDate &&
i.LocationPoints.Distance(location) <= radius)
.GroupBy(i => i.Geography)
.SelectMany(g => g.OrderBy(x => x.EventDateTime).Take(3))
.Select(i => new EventResult { //fill view model here })
.ToPagedList(Page, 10);
I have a survey where users can post answers and since the answers are being saved in the db as a foreign key for each question, I'd like to know which answer got the highest rating.
So if the DB looks somewhat like this:
answer_id
1
1
2
how can I find that the answer with an id of 1 was selected more times than the one with an id of 2 ?
EDIT
So far I've done this:
#question = AnswerContainer.where(user_id: params[:user_id]) which lists the things a given user has voted for, but, obviously, that's not what I need.
you could try:
YourModel.group(:answer_id).count
for your example return something like: {1 => 2, 2 => 1}
You can do group by and then sort
Select answer_id, count(*) as maxsel
From poll
Group by answer_id
Order by maxsel desc
As stated in rails documentation (http://api.rubyonrails.org/classes/ActiveRecord/Calculations.html) when you use group with count, active record "returns a Hash whose keys represent the aggregated column, and the values are the respective amounts"
Person.group(:city).count
# => { 'Rome' => 5, 'Paris' => 3 }
I need some help creating an LINQ select, i have a table with some columns in it, but only 2 of interest to this problem.
userid, type
Now this table have many thousands entries, and I only want the top, let’s say 50. So far so good, but the hard part is that there a lot of rows in success that should only be counted as 1.
Example
Type UserId
============
Add 1
Add 1
Add 1
Add 2
I would like this to only be counted as 2 in the limit of rows I am taking out, but I would like all the rows to be outputted still.
Is this possible with a single SQL request, or should I find another way to do this?
Edit: I can add columns to the table, with values if this would solve the problem.
Edit2: Sotred procedures are also an solution
Example 2: This should be counted as 3 rows
Type UserId
============
Add 1
Add 1
Add 2
Add 1
Are you stuck on LINQ?
Add a PK identity.
Order by PK.
Use a DataReader and just count the changes.
Then just stop when the changes count is at your max.
If you are not in a .NET environment then same thing with a cursor.
Since LINQ is deferred you might be able to just order in LINQ and then on a ForEach just exit.
I'm not close to a computer right now so I'm not sure is 100% correct syntax wise, but I believe you're looking for something like this:
data.Select(x => new {x.Type, x.UserId})
.GroupBy(x => x.UserId)
.Take(50);
You could do it with Linq, but it may be a LOT slower than a traditional for loop. One way would be:
data.Where((s, i) => i == 0 ||
!(s.Type == data[i-1].Type && s.UserId == data[i-1].UserId))
That would skip any "duplicate" items that have the same Type and UserID as the "previous" item.
However this ONLY works if data has an indexer (an array or something that implements IList). An IEnumerable or IQueryable would not work. Also, it is almost certainly not translatable to SQL so you'd have to pull ALL of the results and filter in-memory.
If you want to do it in SQL I would try either scanning a cursor and filling a temp table if one of the values change or using a common table expression that included a ROW_NUMBER column, then doing a look-back sub-query similar to the Linq method above:
WITH base AS
(
SELECT
Type,
UserId,
ROW_NUMBER() OVER (ORDER BY ??? ) AS RowNum
FROM Table
)
SELECT b1.Type, b1.UserId
FROM base b1
LEFT JOIN base b2 ON b1.RowNum = b2.RowNum - 1
WHERE (b1.Type <> b2.Type OR b1.UserId <> b2.UserId)
ORDER BY b1.RowNum
You can do this with LINQ, but I think it might be easier to go the "for(each) loop" route...
data.Select((x, i) => new { x.Type, x.UserId, i })
.GroupBy(x => x.Type)
.Select(g => new
{
Type = g.Key,
Items = g
.Select((x, j) => new { x.UserId, i = x.i - j })
})
.SelectMany(g => g.Select(x => new { g.Type, x.UserId, x.i }))
.GroupBy(x => new { x.Type, x.i })
.Take(50);
.SelectMany(g => g.Select(x => new { x.Type, x.UserId }));
I'm using group_by in a DBIx::Class resultset search. The result returned for each group is always the row in the group with the lowest id (i.e the oldest row in the group). I'm looking for a way to get the row with the highest id (i.e. the newest row in the group) instead.
The problem is fundamentally the same as this:
Retrieving the last record in each group
...except that I'm using DBIx::Class not raw SQL.
To put the question in context:
I have a table of music reviews
review
------
id
artist_id
album_id
pub_date
...other_columns...
There can be multiple reviews for any given artist_id/album_id.
I want the most recent reviews, in descending date order, with no more than one review per artist_id/album_id.
I tried to do this using:
$schema->resultset('Review')->search(
undef,
{
group_by => [ qw/ artist_id album_id / ],
order_by => { -desc => 'pub_date' },
}
);
This nearly works, but returns the oldest review in each group instead of the newest.
How can I get the newest?
For this to work you are relying on broken database behaviour. You should not be able to select columns from a table when you use group by unless they use an aggregate function (min, max etc.) or are specified in the group by clause.
In MySQL, even the manual admits this is wrong - though it supports it.
What I think you need to do is get the latest dates of the reviews, with max(pub_date):
my $dates = $schema->resultset('Review')->search({},
{
select => ['artist_id', 'album_id', {max => 'pub_date'}],
as => [ qw(artist_id album_id recent_pub_date) ],
group_by => [ qw(artist_id album_id) ],
}
);
Then loop through to get the review:
while (my $review_date = $dates->next) {
my $review = $schema->resultset('Review')->search({
artist_id => $review_date->artist_id,
album_id => $review_date->album_id,
pub_date => $review_date->get_column('recent_pub_date'),
})->first;
}
Yep - it's more queries but it makes sense - what if two reviews are on the same date - how should the DB know which one to return in the select statement?
I am a bit stumped on this. Basically I have two tables:
Page:
id
name
Points:
id-
pageid
points
I am looking to get the records from the Page table, and sort it by the amount of points it has in the Points table (the points field)
Currently I have:
$dataProvider=new CActiveDataProvider('Page',array(
'criteria'=>array(
'condition'=>"active = 1 AND userid IN (".$ids.")",
'order'=>"???",
),
'pagination'=>array(
'pageSize'=>30,
),
));
I just don't know how to sort it by the Points table value for the relevant record
I have set up a relation for the Page/Points tables like so:
(in the Page model)
'pagepoints' => array(self::HAS_ONE, 'Points', 'pageid'),
Thanks
You need to do two things:
Add the pagepoints relation to the with part of the query criteria
Reference the column you want to sort by in the order part of the criteria
I 've marked the lines where this happens in the code below:
$dataProvider = new CActiveDataProvider('Page', array(
'criteria'=>array(
'with' => array('pagepoints'), // #1
'condition' => 'active = 1 AND userid IN ('.$ids.')',
'order' => 'pagepoints.points', // #2
),
'pagination'=>array(
'pageSize'=>30,
),
));
What you need to know to understand how this works is that when Yii builds the SQL query (which is a LEFT OUTER JOIN to the Points table), it uses the name you gave to the relation in the Page model (you give the definition for this, it's pagepoints) to alias the joined table. In other words, the query looks like:
SELECT ... FROM Page ... LEFT OUTER JOIN `Points` `pagepoints` ...
It follows that the correct specification for the sort order is pagepoints.points: pagepoints is the table alias, and points is the column in that table.
Try the following
$dataProvider=new CActiveDataProvider('Page',array(
'criteria'=>array(
'with'=>array('pagepoints'),
'condition'=>"active = 1 AND userid IN (".$ids.")",
'order'=>"t.points DESC",
),
'pagination'=>array(
'pageSize'=>30,
),
));
this is the sql you want to generate:
select * from page inner join points
on page.id = points.page_id order by
points.points desc