I have a test database which logs data from when a store logs onto a store portal and how long it stays logged on.
Example:
(just for visualizing purposes - not actual database)
Stores
Id Description Address City
1 Candy shop 43 Oxford Str. London
2 Icecream shop 45 Side Lane Huddersfield
Connections
Id Store_Ref Start End
1 2 2011-02-11 09:12:34.123 2011-02-11 09:12:34.123
2 2 2011-02-11 09:12:36.123 2011-02-11 09:14:58.125
3 1 2011-02-14 08:42:10.855 2011-02-14 08:42:10.855
4 1 2011-02-14 08:42:12.345 2011-02-14 08:50:45.987
5 1 2011-02-15 08:35:19.345 2011-02-15 08:38:20.123
6 2 2011-02-19 09:08:55.555 2011-02-19 09:12:46.789
I need to get various data from the database. I've already gotten the max and average connection duration. (So probably very self-evident that..) I also need to have some information about which connection lasted the least. I ofcourse immediately thought of the Min() function of Linq, but as you can see, the database also includes connections that started and ended instantly. Therefore, that data isn't actually "valid" for data analysis.
So my question is how to get the minimum value, but if the value = 0, get the next value that is the lowest.
My linq query so far (which implements the Min() function):
var min = from connections in Connections
join stores in Stores
on connections.Store_Ref equals stores.Id
group connections
by stores.Description into groupedStores
select new
{
Store_Description = groupedStores.Key,
Connection_Duration = groupedStores.Min(connections =>
(SqlMethods.DateDiffSecond(connections.Start, connections.End)))
};
I know that it's possible to get the valid values through multiple queries and/or statements though, but I was wondering if it's possible to do it all in just one query, since my program expects linq queries to be returned and my preference goes to keeping the program as "light" as possible.
If you have to great/simple method to do so, please share it. Your contribution is very appreciated! :)
What if you add, before the select new, a let clause for the duration of the conection with something like:
let duration = SqlMethods.DateDiffSecond(connections.Start, connections.End)
And then add a where clause
where duration != 0
var min = from connections in Connections.Where(connections => (SqlMethods.DateDiffSecond(connections.Start, connections.End) > 0)
join stores in Stores
on connections.Store_Ref equals stores.Id
group connections
by stores.Description into groupedStores
select new
{
Store_Description = groupedStores.Key,
Connection_Duration = groupedStores.Min(connections =>
(SqlMethods.DateDiffSecond(connections.Start, connections.End)))
};
Try this, With filtering the "0" values you will get the right result, at least that is my taught.
Include a where clause before calculating the Min value.
groupedStores.Where(conn => SqlMethods.DateDiffSecond(conn.Start, conn.End) > 0)
.Min(conn => (SqlMethods.DateDiffSecond(conn.Start, conn.End))
Related
I've been attempting to write a peewee select query which results in a table with 2 counts (one for the number of prizes associated with the lottery, and the for the number of packages associated with the lottery), as well as the fields in the Lottery model.
I've managed to write select queries with 1 count working (seen below), and then I've had to convert the ModelSelects to lists and join them manually (which I think is very hacky).
I did manage to write a select query where the results were joined, but it would multiply the packages count with the prizes count (I've since lost that query).
I also tried using a .switch(Lottery) but I didn't have any luck with this.
query1 = (Lottery.select(Lottery,fn.count(Package.id).alias('packages'))
.join(LotteryPackage)
.join(Package)
.order_by(Lottery.id)
.group_by(Lottery)
.dicts())
query2 = (Lottery.select(Lottery.id.alias('lotteryID'), fn.count(Prize.id).alias('prizes'))
.join(LotteryPrize)
.join(Prize)
.group_by(Lottery)
.order_by(Lottery.id)
.dicts())
lottery = list(query1)
query3 = list(query2)
for x in range(len(lottery)):
lottery[x]['prizes'] = query3[x]['prizes']
While the above code works, is there a cleaner way to write this query?
Your best bet is to do this with subqueries.
# Create query which gets lottery id and count of packages.
L1 = Lottery.alias()
subq1 = (L1
.select(L1.id, fn.COUNT(LotteryPackage.package).alias('packages'))
.join(LotteryPackage, JOIN.LEFT_OUTER)
.group_by(L1.id))
# Create query which gets lottery id and count of prizes.
L2 = Lottery.alias()
subq2 = (L2
.select(L2.id, fn.COUNT(LotteryPrize.prize).alias('prizes'))
.join(LotteryPrize, JOIN.LEFT_OUTER)
.group_by(L2.id))
# Select from lottery, joining on each subquery and returning
# the counts.
query = (Lottery
.select(Lottery, subq1.c.packages, subq2.c.prizes)
.join(subq1, on=(Lottery.id == subq1.c.id))
.join(subq2, on=(Lottery.id == subq2.c.id))
.order_by(Lottery.name))
for row in query.objects():
print(row.name, row.packages, row.prizes)
I am using Neo4j as a database to store voting information related to another database object.
I have a Vote object which has fields:
type:String with values of UP or DOWN.
argId:String which is a string ID value linking to a unique argument object
I am trying to query the number of votes assigned to a given argId using the following queries:
MATCH (v:Vote) WHERE v.argId = '214' AND v.type='DOWN'
RETURN {downvotes: COUNT(v)} AS votes
UNION
MATCH (v:Vote) WHERE v.argId = '214' AND v.type='UP'
RETURN {upvotes: COUNT(v)} AS votes
Note that this above cypher -- works and returns the expected result result like so:
[
{
"downvotes": 1
},
{
"upvotes": 10
}
]
But I feel like the query could be a bit neater and want to write something like this:
MATCH (v:Vote) WHERE v.argId = '214' AND v.type='UP'
MATCH (b:Vote) WHERE b.argId = '214' AND b.type='DOWN'
RETURN {upvotes: COUNT(v), downvotes: COUNT(b)}
Just reading it through, I think it makes sense, b and v are declared as separate variables, so all should be good (so I thought).
But running it given me this:
{
"upvotes": 10,
"downvotes": 10
}
But it should be what I have above.
Why is this?
I'm kinda new to neo4j and cypher so I've probably not understood how cypher works fully.
Can anyone shine any light?
Thank you!
p.s. I'm using Neo4j 3.5.6 and running the queries via the Desktop web browser app.
I think if you run this query you will get a clearer picture of what is happeneing. Your query produces a cartesian product of the upvotes(10) and the downvotes(1). The product is a result set of 10 rows. When they are subsequently counted, there are ten of each.
MATCH (v:Vote) WHERE v.argId = '214' AND v.type='UP'
MATCH (b:Vote) WHERE b.argId = '214' AND b.type='DOWN'
RETURN v.type, b.type
In order to get the result you want you need to filter the values and count them individually.
Rather than have two match statements, have a single match statement that retreives all of the values of interest and then use a conditional statement to filter them into upvotes and downbotes buckets.
Something like this may suit you.
MATCH (v:Vote {argId: '214'})
WHERE v.type IN ['UP', 'DOWN']
RETURN {
upvotes: count(CASE WHEN v.type = 'DOWN' THEN 1 END),
downvotes: count(CASE WHEN v.type = 'UP' THEN 1 END)
} AS vote_result
Using APOC you could do something like this whereby you use the type values themselves to aggregate the counts and then use APOC to convert it to a map with the types as the keys in the map.
MATCH (v:Vote {argId: '214'})
WHERE v.type IN ['UP', 'DOWN']
WITH [v.type, count(*)] AS vote_pair
RETURN apoc.map.fromPairs(collect(vote_pair)) AS votes
In my problem which I am trying to solve, there is a performance values table:
Staff PerformanceID Date Percentage
--------------------------------------------------
StaffName1 1 2/15/2016 95
StaffName1 2 2/15/2016 95
StaffName1 1 2/22/2016 100
...
StaffName2 1 2/15/2016 100
StaffName2 2 2/15/2016 100
StaffName2 1 2/22/2016 100
And the SQL statement as follows:
SELECT TOP (10)
tbl_Staff.StaffName,
ROUND(AVG(tbl_StaffPerformancesValues.Percentage), 0) AS AverageRating
FROM
tbl_Staff
INNER JOIN
tbl_AcademicTermsStaff ON tbl_Staff.StaffID = tbl_AcademicTermsStaff.StaffID
INNER JOIN
tbl_StaffPerformancesValues ON tbl_AcademicTermsStaff.StaffID = tbl_StaffPerformancesValues.StaffID
WHERE
(tbl_StaffPerformancesValues.Date >= #DateFrom)
AND (tbl_AcademicTermsStaff.SchoolCode = #SchoolCode)
AND (tbl_AcademicTermsStaff.AcademicTermID = #AcademicTermID)
GROUP BY
tbl_Staff.StaffName
ORDER BY
AverageRating DESC, tbl_Staff.StaffName
What I am trying to do is, from a given date, for instance 02-22-2016,
I want to calculate average performance for each staff member.
The code above gives me average without considering the date filter.
Thank you.
Apart from your join conditions and table names which looks quite complex, One simple question, If you want the results for a particular date then why is the need of having
WHERE tbl_StaffPerformancesValues.Date >= #DateFrom
As you said your query is displaying average results but not for a date instance. Change the above line to WHERE tbl_StaffPerformancesValues.Date = #DateFrom.
Correct me if I am wrong.
Thanks for the replies, the code above, as you all say and as it is also expected is correct.
I intended to have a date filter to see the results from the given date until now.
The code
WHERE tbl_StaffPerformancesValues.Date >= #DateFrom
is correct.
The mistake i found from my coding is, in another block i had the following:
Protected Sub TextBoxDateFrom_Text(sender As Object, e As System.EventArgs) Handles TextBoxDate.PreRender, TextBoxDate.TextChanged
Try
Dim strDate As String = Date.Parse(DatesOfWeekISO8601(2016, WeekOfYearISO8601(Date.Today))).AddDays(-7).ToString("dd/MM/yyyy")
If Not IsPostBack Then
TextBoxDate.Text = strDate
End If
SqlDataSourcePerformances.SelectParameters("DateFrom").DefaultValue = Date.Parse(TextBoxDate.Text, CultureInfo.CreateSpecificCulture("id-ID")).AddDays(-7)
GridViewPerformances.DataBind()
Catch ex As Exception
End Try
End Sub
I, unintentionally, applied .AddDays(-7) twice.
I just noticed it and removed the second .AddDays(-7) from my code.
SqlDataSourcePerformances.SelectParameters("DateFrom").DefaultValue = Date.Parse(TextBoxDate.Text, CultureInfo.CreateSpecificCulture("id-ID"))
Because of that mistake, the SQL code was getting the performance values 14 days before until now. So the average was wrong.
Thanks again.
I'm building an application that needs to allow the user to filter a data table according to different filters. So, the user will have three different filter posibilites but he might use only one, or two or the three of them at the same tame.
So, let's say I have the following columns on the table:
ID (int) PK
Sede (int)
Programa (int)
Estado (int)
All of those columns will store numbers, integers. The "ID" column is the primary key, "Sede" stores 1 or 2, "Programa" is any number between 1 and 15, and "Estado" will store numbers between 1 and 13.
The user may filter the data stored in the table using any of those filters (Sede, Programa or Estado). But the might, as well, use two filters, or the three of them at the same time.
The idea is that this application works like the data filters on Excel. I created a simulated table on excel to show what I want to achieve:
This first image shows the whole table, without applying any filter.
Here, the user selected a filter for "Sede" and "Programa" but leaved the "Estado" filter empty. So the query returns the values that are equal to the filter, but leaves the "Estado" filter open, and brings all the records, filering only by "Sede" (1) and "Programa" (6).
In this image, the user only selected the "Estado" filter (5), so it brings all the records that match this criteria, it doesn't matter if "Sede" or "Programa" are empty.
If I use a SELECT clasuse with a WHERE on it, it will work, but only if the three filters have a value:
DECLARE #sede int
DECLARE #programa int
DECLARE #estado int
SET #sede = '1'
SET #programa = '5'
SET #estado = '12'
SELECT * FROM [dbo].[Inscripciones]
WHERE
([dbo].[Inscripciones].[Sede] = #sede)
AND
([dbo].[Inscripciones].[Programa] = #programa)
AND
([dbo].[Inscripciones].[Estado] = #estado)
I also tryed changing the "AND" for a "OR", but I can't get the desired result.
Any help will be highly appreciated!! Thanks!
common problem: try using coalesce on the variable and for the 2nd value use the field name you're comparing to. Be careful though; Ensure it's NULL and not empty string being passed!
What this does is take the first non-null value of the variable passed in or the value you're comparing to.. Thus if the value passed in is null the comparison will always return true.
WHERE
[dbo].[Inscripciones].[Sede] = coalesce(#sede, [dbo].[Inscripciones].[Sede])
AND
[dbo].[Inscripciones].[Programa] = coalesce(#programa, [dbo].[Inscripciones].[Programa])
AND
[dbo].[Inscripciones].[Estado] = coalesce(#estado, [dbo].[Inscripciones].[Estado])
If sede is null and programa and estado are populated the compare would look like...
?=? (or 1=1)
?=programa variable passed in
?=Estado variable passed in
Boa Sorte!
Thank you all for your anwers. After reading the article posted in the comments by #SeanLange I was finally able to achieve what was needed. Using a CASE clause in the WHERE statement solves the deal. Here's the code:
SELECT
*
FROM [dbo].[Inscripciones]
WHERE
([dbo].[Inscripciones].[Sede] = (CASE WHEN #sede = '' THEN [dbo].[Inscripciones].[Sede] ELSE #sede END))
AND
([dbo].[Inscripciones].[Programa] = (CASE WHEN #programa = '' THEN [dbo].[Inscripciones].[Programa] ELSE #programa END))
AND
([dbo].[Inscripciones].[Estado] = (CASE WHEN #estado = '' THEN [dbo].[Inscripciones].[Estado] ELSE #estado END))
AND
([dbo].[Inscripciones].[TipoIngreso] = (CASE WHEN #tipoingreso = '' THEN [dbo].[Inscripciones].[TipoIngreso] ELSE #tipoingreso END))
Thanks again!!
I have a LINQ to SQL query:
from at in Context.Transaction
select new {
at.Amount,
at.PostingDate,
Details =
from tb in at.TransactionDetail
select new {
Amount = tb.Amount,
Description = tb.Desc
}
}
This results in one SQL statement being executed. All is good.
However, if I attempt to return known types from this query, even if they have the same structure as the anonymous types, I get one SQL statement executed for the top level and then an additional SQL statement for each "child" set.
Is there any way to get LINQ to SQL to issue one SQL statement and use known types?
EDIT: I must have another issue. When I plugged a very simplistic (but still hieararchical) version of my query into LINQPad and used freshly created known types with just 2 or 3 members, I did get one SQL statement. I will post and update when I know more.
EDIT 2: This appears to be due to a bug in Take. See my answer below for details.
First - some reasoning for the Take bug.
If you just Take, the query translator just uses top. Top10 will not give the right answer if cardinality is broken by joining in a child collection. So the query translator doesn't join in the child collection (instead it requeries for the children).
If you Skip and Take, then the query translator kicks in with some RowNumber logic over the parent rows... these rownumbers let it take 10 parents, even if that's really 50 records due to each parent having 5 children.
If you Skip(0) and Take, Skip is removed as a non-operation by the translator - it's just like you never said Skip.
This is going to be a hard conceptual leap to from where you are (calling Skip and Take) to a "simple workaround". What we need to do - is force the translation to occur at a point where the translator can't remove Skip(0) as a non-operation. We need to call Skip, and supply the skipped number at a later point.
DataClasses1DataContext myDC = new DataClasses1DataContext();
//setting up log so we can see what's going on
myDC.Log = Console.Out;
//hierarchical query - not important
var query = myDC.Options.Select(option => new{
ID = option.ParentID,
Others = myDC.Options.Select(option2 => new{
ID = option2.ParentID
})
});
//request translation of the query! Important!
var compQuery = System.Data.Linq.CompiledQuery
.Compile<DataClasses1DataContext, int, int, System.Collections.IEnumerable>
( (dc, skip, take) => query.Skip(skip).Take(take) );
//now run the query and specify that 0 rows are to be skipped.
compQuery.Invoke(myDC, 0, 10);
This produces the following query:
SELECT [t1].[ParentID], [t2].[ParentID] AS [ParentID2], (
SELECT COUNT(*)
FROM [dbo].[Option] AS [t3]
) AS [value]
FROM (
SELECT ROW_NUMBER() OVER (ORDER BY [t0].[ID]) AS [ROW_NUMBER], [t0].[ParentID]
FROM [dbo].[Option] AS [t0]
) AS [t1]
LEFT OUTER JOIN [dbo].[Option] AS [t2] ON 1=1
WHERE [t1].[ROW_NUMBER] BETWEEN #p0 + 1 AND #p1 + #p2
ORDER BY [t1].[ROW_NUMBER], [t2].[ID]
-- #p0: Input Int (Size = 0; Prec = 0; Scale = 0) [0]
-- #p1: Input Int (Size = 0; Prec = 0; Scale = 0) [0]
-- #p2: Input Int (Size = 0; Prec = 0; Scale = 0) [10]
-- Context: SqlProvider(Sql2005) Model: AttributedMetaModel Build: 3.5.30729.1
And here's where we win!
WHERE [t1].[ROW_NUMBER] BETWEEN #p0 + 1 AND #p1 + #p2
I've now determined this is the result of a horrible bug. The anonymous versus known type turned out not to be the cause. The real cause is Take.
The following result in 1 SQL statement:
query.Skip(1).Take(10).ToList();
query.ToList();
However, the following exhibit the one sql statement per parent row problem.
query.Skip(0).Take(10).ToList();
query.Take(10).ToList();
Can anyone think of any simple workarounds for this?
EDIT: The only workaround I've come up with is to check to see if I'm on the first page (IE Skip(0)) and then make two calls, one with Take(1) and the other with Skip(1).Take(pageSize - 1) and addRange the lists together.
I've not had a chance to try this but given that the anonymous type isn't part of LINQ rather a C# construct I wonder if you could use:
from at in Context.Transaction
select new KnownType(
at.Amount,
at.PostingDate,
Details =
from tb in at.TransactionDetail
select KnownSubType(
Amount = tb.Amount,
Description = tb.Desc
)
}
Obviously Details would need to be an IEnumerable collection.
I could be miles wide on this but it might at least give you a new line of thought to pursue which can't hurt so please excuse my rambling.