Right now I use this search to find items for certain category in my database
#items=Item.where(:category_id => #active_category_id).order(:price)
But recently I added a column to Item table called detail. It can be 0 or 1 and it is integer or it can be empty cause I added it just now and I had already some items in my db.
So now I need two searches: I need search that returns items with detail=1
And where detail is not 1.
So I do it like this:
#for items with detail = 1
#items=Item.where(:category_id => #active_category_id)
.where(:detail=> 1).order(:price)
It is working.
But now I need to find items with detail != 1
So I write
#items=Item.where(:category_id => #active_category_id)
.where.not(:detail=> 1).order(:price)
And it is not working. What do I do?
NULL values will not match an equality or inequality. You have to explicity compare to NULL. Try Item.where(detail: nil).
If you need 0 OR NULL you might need to write raw SQL: Item.where("detail = 0 OR detail IS NULL")
You might also consider backfilling your db to eliminate the NULL values, then you can just compare with 1 and 0.
Related
I have values in a table called Translation, that contains for every values per example:
=> {"fr"=>"Jaune", "de"=>"", "en"=>"", "bg"=>"", "hr"=>"", "es"=>"", "hu"=>"", "it"=>"", "lt"=>"", "lv"=>"", "nl"=>"", "pl"=>"", "pt"=>"", "ro"=>"", "cs"=>""}
and I'm looking to get the the number of the translation for each language:
I'm trying :
Translation.where("values->>'fr' IS NOT NULL").count
but it giving me 0, which is not correct, do anyone knows how to do it correctly?
The problem that you have is that the keys that don't have values, still exist in the json, so "is not null" will return all of them because the key exist. you have two options here, you can remove the empty keys from the database, so not null will work, or, change it to see if the key is empty
You can do it like this
Translation.where("values->>'fr' <> ''").count
and it will work with the structure that you have right now.
I'm using Rails to search through a SQLite table (for other reasons I can't use the standard database-model system) using a SELECT query like so:
info = ActiveRecord::Base.connection.execute("SELECT * FROM #{form_name} WHERE EmailAddress = \"#{user_em}\";")
This returns the correct values, but for some reason the output is in duplicate, the difference being the 2nd set doesn't have column titles in the hash, instead going from 0-[num columns]. For example:
{"id"=>1, "Timestamp"=>"2/27/2017 14:26:03", "EmailAddress"=>"-snip-", 0=>1, 1=>"2/27/2017 14:26:03", 2=>"-snip-"}
(I'll note the obvious- there's only one row in the table with that information in it)
While it's not exactly a fatal problem, I'm interested as to why it's doing so and if it's possible to prevent it. Thanks!
This allows you to read the values both by column index or column name:
id = row[0]
timestamp = row["Timestamp"]
I have a table that looks like the following:
ID City Code
"1005AE" "Oakland" "Value1"
"1006BR" "St.Louis" "Value2"
"102AC" "Miami" "Value1"
"103AE" "Denver" "Value3"
And I want to transpose/pivot the Code examples/values into column attributes like this:
ID City Value1 Value2 Value3
"1005" "Oakland" 1 0 0
"1006" "St.Louis" 0 1 0
"1012" "Miami" 1 0 0
"1030" "Denver" 0 0 1
Note that the ID field is numeric values encoded as strings because Rapidminer had trouble importing bigint datatypes. So that is a separate issue I need to fix--but my focus here is the pivoting or transposing of the data.
I read through a few different Stackoverflow posts listed below. They suggested the Pivot or Transpose operations. I tried both of these, but for some reason I am getting either a huge table which creates City as a dummy variable as well, or just some subset of attribute columns.
How can I set the rows to be the attributes and columns the samples in rapidminer?
Rapidminer data transpose equivalent to melt in R
Any suggestions would be appreciated.
In pivoting, the group attribute parameter dictates how many rows there will be and the index attribute parameter dictates what the last part of the name of new attributes will be. The first part of the name of each new attribute is driven by any other regular attributes that are neither group nor index and the value within the cell is the value found in the original example set.
This means you have to create a new attribute with a constant value of 1; use Generate Attributes for this. Set the role of the ID attribute to be ID so that it is no longer a regular attribute; use Set Role for this. In the Pivot operator, set the group attribute to be City and the index attribute to be Code. The end result is close to what you want. The final steps are, firstly to set missing values to be 0; use Replace Missing Values for this and, secondly to rename the attributes to match what you want; use Rename for this.
You will have to join the result back to the original since the pivot operation loses the ID.
You can find a worked example here http://rapidminernotes.blogspot.co.uk/2011/05/worked-example-using-pivot-operator.html
Hopefully this is a little clearer. I'm sorry but I'm very new to coding in general. I have multiple tables that I have to query in succession in order to get to the correct array that I need. The following logic for the query is as follows:
this gives me an array based upon the store :id
store = Stores.find(params[:id])
this gives me another array based upon the param .location found in the table store where that value equals the row ID in the table Departments
department = Departments.find(store.location)
I need to preform one last query but in order to do so I need to figure out which day of the meeting is needed. In order to do this I have to create the parameter day_of_meeting found in the table Stores. I try to call it from the array above and create a new variable. In the Table Departments, I there are params such as day_1, day_2 and so on. I need to be able to call something like department.day_1 or department.day_2. Thus, I'm trying to actually create the variable by join the words "department.day_" to the variable store.day_of_meeting which would equal some integer, creating department.day_1...
which_day = ["department.day_", store.day_of_meeting].join("")
This query finds uses the value found from the variable department.day_1 to query table Meeting to find the values in the corresponding row.
meeting = Meeting.find(which_day)
Does this make my problem any clearer to understand?
findmethod can only accept parameters like Meeting.find(1) or Meeting.find("1-xx").
so, what you need is Meeting.find(department.send("day_" + store.day_of_meeting.to_s))
Hope to help!
I am working on an asp.net mvc web application, and I am using Sql server 2008 R2 + Entity framework.
Now on the sql server I have added a unique index on any column that might be ordered by . for example I have created a unique index on the Sql server on the Tag colum and I have defined that the sort order for the index to be Ascending. Now I have some queries inside my application that order the tag ascending while other queries order the Tag descending, as follow:-
LatestTechnology = tms.Technologies.Where(a=> !a.IsDeleted && a.IsCompleted).OrderByDescending(a => a.Tag).Take(pagesize).ToList(),;
TechnologyList = tms.Technologies.Where(a=> !a.IsDeleted && a.IsCompleted).OrderBy (a => a.Tag).Take(pagesize).ToList();
So my question is whether the two OrderByDescending(a => a.Tag). & OrderBy(a => a.Tag), can benefit from the asending unique index on the sql server on the Tag colum ? or I should define two unique indexes on the sql server one with ascending sort order while the other index with decedning sort order ?
THanks
EDIT
the following query :-
LatestTechnology = tms.Technologies.Where(a=> !a.IsDeleted && a.IsCompleted).OrderByDescending(a => a.Tag).Take(pagesize).ToList();
will generate the following sql statement as mentioned by the sql server profiler :-
SELECT TOP (15)
[Extent1].[TechnologyID] AS [TechnologyID],
[Extent1].[Tag] AS [Tag],
[Extent1].[IsDeleted] AS [IsDeleted],
[Extent1].[timestamp] AS [timestamp],
[Extent1].[TypeID] AS [TypeID],
[Extent1].[StartDate] AS [StartDate],
[Extent1].[IT360ID] AS [IT360ID],
[Extent1].[IsCompleted] AS [IsCompleted]
FROM [dbo].[Technology] AS [Extent1]
WHERE ([Extent1].[IsDeleted] <> cast(1 as bit)) AND ([Extent1].[IsCompleted] = 1)
ORDER BY [Extent1].[Tag] DESC
To answer your question:
So my question is whether the two OrderByDescending(a => a.Tag). &
OrderBy(a => a.Tag), can benefit from the asending unique index on the
sql server on the Tag colum ?
Yes, SQL Server can read an index in both directions: as in index definition or in the exact opposite direction.
However, from your intro I suspect that you still have a wrong impression how indexing works for order by. If you have both, a where clause and an order by clause, you must make sure to have a single index that covers both clauses! It does not help to have on index for the where clause (like on isDeleted and isCompleted — whatever that is in your example) and another index on tag. You need to have a single index that first has the columns of the where clause followed by the columns of the order by clause (multi-column index).
It can be tricky to make it work correctly, but it's worth the effort especially if your are only fetching the first few rows (like in your example).
If it doesn't work out right away, please have a look at this:
http://use-the-index-luke.com/sql/sorting-grouping/indexed-order-by
It is generally best to show the actual SQL query—not the .NET source code—when asking for performance advice. Then I could tell you which index to create exactly. At the moment I'm unsure about isDeleted and isCompleted — are these table columns or expressions that evaluate upon other columns?
EDIT (after you added the SQL query)
There are two ways to make your query work as indexed top-n query:
http://sqlfiddle.com/#!6/260fb/4
The first option is a regular index on the columns from the where clause followed by those from the order by clause. However, as you query uses this filter IsDeleted <> cast(1 as bit) it cannot use the index in a order-preserving way. If, however, you re-phrase the query so that it reads like this IsDeleted = cast(0 as bit) then it works. Please look at the fiddle, I've prepared everything there. Yes, SQL Server could be smart enough to know that, but it seems like it isn't.
I don't know how to tweak EF to produce the query in the above described way, sorry.
However, there is a second option using a so called filtered index — that is an index that only contains a sub-set of the table rows. It's also in the SQL Fiddle. Here it is important that you add the where clause to the index definition in the very same way as it appears in your query.
In both ways it still works if you change DESC to ASC.
The important part is that the execution plan doesn't show a sort operation. You can also verify this in SQL Fiddle (click on 'View execution plan').