i'm in a situation my mind is blocked en hope someone can help me.
I have two tables. One table with customers of a subsription service and one invoice table.
these tables are not linked with keys in the database for keeping history of invoices if customers are deleted. This way I have to query the customers table joining the invoiceheader table by another unique contraint (not know by the database). This constraint is using name and address together.
An invoice is send one time a year. In the invoice-header table the date is stored when the invoice is created. In a couple of years constomers can have multiple invoices.
i'm trying to create a linq query but i'm looking the wrong way for a solution I'm afraid.
who can point me the right way?
for now i have a query :
var temp = from c in context.customer
from i in context.invoiceheader
where c.name + c.address == i.name + i.address
&& i.invoicedate < DateTime.Now.Year
select c;
With this query I get all customers who have receive an invoice last year and stil have subscribed. The trouble is with new customers who never received an invoice.
What to do for customers where in this case they haven't any invoice records.?
summurized: I want to query the last know invoice. If this invoice is older than a year (previous year)or no invoice is sent at al, i wanna retreive a list of customers the should be sent a new invoice.
I guess that what you want is a left outer join - this way you should be able to get all the customers you need:
var customers = from c in context.customer
join i in context.invoiceheader
on c.Name + c.Address equals i.Name + i.Address
into g
from row in g.DefaultIfEmpty()
where row == null ||row.invoicedate < DateTime.Now.Year
select c;
Related
First, I know there is a common issue in Stack Overflow, but the following solutions are not working well here. So I still need some help.
Oracle - Update COUNT of rows with specific value
Oracle - Update rows with a min value in the group of a column from another table
Oracle update statement with group function
Oracle - Update COUNT of rows with specific value
The problem is: I have a +700k lines table:
REVIEWS (PRODUCT_ID, REVIEW, REVIEW_DATE, RELEASE_DATE, ..., REVIEW_COUNT)
I'm trying to update REVIEW_COUNT by counting the lines with the same PRODUCT_ID (I want just reviews before product release). So the code below works very well for my purpose:
SELECT COUNT(PRODUCT_ID) FROM REVIEWS
WHERE REVIEW_DATE < RELEASE_DATE
GROUP BY PRODUCT_ID
But I'm having a hard time to do the update. First I tried this:
UPDATE REVIEWS R
SET R.REVIEWS_COUNT =
(SELECT COUNT(RR.PRODUCT_ID) FROM REVIEWS RR
WHERE RR.DATA < RR.REL_DATE
GROUP BY RR.PRODUCT_ID)
The error is "more than one row", which is not surprising, but since I'm using the group by statement, it shouldn't occur. So I tried a self-join:
UPDATE REVIEWS R
SET R.REVIEWS_COUNT =
(SELECT COUNT(RR.PRODUCT_ID) FROM REVIEWS RR
WHERE RR.PRODUCT_ID = R.PRODUCT_ID AND RR.DATA < RR.REL_DATE)
But the query is taking forever and I don't think that should take so long, the simple select is pretty normal-fast.
I've also tested some more fancy and more simple stuff, but the outcome remains the same: long time waiting and it seems just wrong.
Please, what I'm missing in such easy update?
Maybe instead of updating you could define view:
select product_id, review_date, release_date,
count(case when review_date < release_date then 1 end)
over (partition by product_id) review_count
from reviews;
You could also try merge instead update:
merge into reviews a
using (select product_id, count(product_id) cnt from reviews
where review_date < release_date
group by product_id ) b
on (a.product_id = b.product_id)
when matched then update set reviews_count = b.cnt
dbfiddle
I think your second update is correct:
UPDATE REVIEWS R
SET R.REVIEWS_COUNT =
(SELECT COUNT(RR.PRODUCT_ID) FROM REVIEWS RR
WHERE RR.PRODUCT_ID = R.PRODUCT_ID AND RR.DATA < RR.REL_DATE)
;
This will update every record in the reviews table. Is that what you wanted?
An index on product_id will make the inner query run faster, but it will still update all 700K or so records.
I'm trying to create a database view via a migration in Laravel 5.2 as I need to hand a fairly complex query to a view. I have models / tables for leagues, teams, players, and points. Each one has a hasMany / belongsTo relationship with the one before it. The goal is to create a table where each row is a league name, a sum of all remaining points for the league, and a count of points.remnants where the value of points.remnants > 4.
Major Edit:
What I have so far is
DB::statement( 'CREATE VIEW wones AS
SELECT
leagues.name as name,
sum(points.remnants) as trem,
count(case when points.remnants < 4 then 1 end) as crem
FROM leauges
JOIN teams ON (teams.league_id = leagues.id)
JOIN players ON (players.team_id = teams.id)
JOIN points ON (points.player_id = players.id);
' );
This does not throw any errors, but it only returns one row and the sum is for all points in all leagues.
What I'm looking for is to create a table where there is a row for each league, that has league name, total remaining points for that league, and total points with less than 4 remaining per league.
Marked as solved. See the accepted answer for most of this issues. The one row problem was because I wasn't using GROUP BY with the count().
It looks to me like the problem is your SQL syntax. Here's what you wrote:
CREATE VIEW wones AS SELECT (name from leagues) AS name
join teams where (leagues.id = team.country_id)
join players where (teams.id = players.team_id)
join points where (players.id = points.player_id)
sum(points.remnants) AS trem
count(points.remnants where points.remnants < 4) AS crem
The problem is with the way you've mixed FROM and JOIN clauses with column specifications. Try this:
CREATE VIEW wones AS
SELECT
leagues.name,
sum(points.remnants) AS trem
sum(IF(points.remnants<4, 1, 0)) AS crem
FROM leagues
JOIN teams ON (leagues.id = team.country_id)
JOIN players ON (teams.id = players.team_id)
JOIN points ON (players.id = points.player_id);
I've reformatted it a bit to make it a little clearer. The SQL keywords are capitalized and the various clauses are separated onto their own lines. What we're doing here is specifying the columns, followed by the table specifications - first the leagues table, then the other tables joined to that one.
I would be grateful for help with a LINQ equivalent of the following SQL Query (which works). Below this SQL query I give some description of my simple data base and the problem I want to solve.
Select a.Name, a.OrderID,
b.ProductIDFirst, c1.productName ProductNameFirst,
b.ProductIDSecond , c2.productName ProductNameSecond
from Customers a
INNER JOIN ORDERS b ON a.OrderID = b.OrderID
left join products c1 on b.productidfirst = c1.productid
left join products c2 on b.ProductIDSecond = c2.productid
Background information on the database structure:
I have a simple SQL Server Database with three Tables named Products, Orders and Customers.
The business model is such that each order can have only two products (not more).
The Orders table has two foreign keys, though they both come from the Products table. These Foreign Key field Names in the Orders Table are ProductIDFirst and ProductIDSecond. These two Foreign Keys in the orders table correspond to two products that each order can have. Customers table has one Foreign Key which comes from the Orders Table.
Now I need help with an LINQ query that will return me all customers such that I get five fields - CustomerName, OrderID and Names of each of the two products that match the OrderID in the customer product.
Your links are non-existent, so here's a best attempt without seeing anything.
Assuming you have the following containers (you'll need to change them for your scenario):
var customers = new List<Customer>();
var orders = new List<Order>();
var products = new List<Product>();
You can do the following:
var query =
from a in customers
join b in orders
on a.OrderId equals b.OrderId
join c1 in products
on b.ProductIdFirst equals c1.ProductId into c1a
join c2 in products
on b.ProductIdSecond equals c2.ProductId into c2a
from p1 in c1a.DefaultIfEmpty()
from p2 in c2a.DefaultIfEmpty()
select new
{
Name = a.Name,
OrderId = a.OrderId,
ProductIdFirst = p1 == null ? null : p1.ProductIdFirst,
ProductNameFirst = p1 == null ? null : p1.ProductNameFirst,
ProductIdSecond = p2 == null ? null : p1.ProductIdSecond,
ProductNameSecond = p2 == null ? null : p1.ProductNameSecond,
};
In short, where you want a left join, project the join into something else (e.g. c1a, c2a) then call from on them using DefaultIfEmpty() which will set null when no matching item exists on the right-hand-side.
I am trying to get all records from an entity that do not join to another entity.
This is what I am trying to do in SQL:
SELECT * from table1
LEFT join table2
ON table1.code = table2.code
WHERE table2.code IS NULL
It results in all table1 rows that did not join to table2.
I have it working with Linq when joining on one field, but I have contact records to join on firstname, dob, and number.
I have a "staging" entity that is imported to; a workflow processes the staging records and creates contacts if they are new.
The staging entity is pretty much a copy of the real entity.
var queryable = from staging in linq.mdo_staging_contactSet
join contact in linq.ContactSet
on staging.mdo_code equals contact.mdo_code
into contactGroup
from contact in contactGroup.DefaultIfEmpty()
// all staging records are selected, even if I put a where clause here
select new Contact
{
// import sequence number is set to null if the staging contact joined to the default contact, which has in id of null
ImportSequenceNumber = (contactContactId == null) ? new int?(subImportNo) : null,
/* other fields get populated */
};
return queryable // This is all staging Contacts, the below expressions product only the new Contacts
.AsEnumerable() // Cannot use the below query on IQuerable
.Where(contact => contact.ImportSequenceNumber != null); // ImportSequenceNumber is null for existing Contacts, and not null for new Contacts
Can I do the same thing using method syntax?
Can I do the above and join on multiple fields?
The alternatives I found were worse and involved using newRecords.Except(existingRecords), but with IEnumerables; is there a better way?
You can do the same thing with method calls, but some tend to find it harder to read since there are some LAMBDA expressions in the middle. Here is an example that shows how the two are basically the same.
I've seen others ask this same questions and it boils down to choice by the developer. I personally like the LINQ approach since I also write a bunch of SQL and I can read the code easier.
I have a Contact model which has many Notes. On one page of my app, I show several attributes of a table of contacts (name, email, latest note created_at).
For the note column, I'm trying to write a joins statement that grabs all contacts along with just their latest note (or even just the created_at of it
What I've come up with is incorrect as it limits and orders the contacts, not their notes:
current_user.contacts.joins(:notes).limit(1).order('created_at DESC')
If you just want the created_at value for the most recent note for each contact, you can first create a query to find the max value and then join with that query:
max_times = Note.group(:contact_id).select("contact_id, MAX(created_at) AS note_created_at").to_sql
current_user.contacts.select("contacts.*, note_created_at").joins("LEFT JOIN (#{max_times}) max_times ON contacts.id = max_times.contact_id")
If you want to work with the Note object for the most recent notes, one option would be to select the notes and group them by the contact_id. Then you can read them out of the hash as you work with each Contact.
max_times = Note.group(:contact_id).select("contact_id, MAX(created_at) AS note_created_at").to_sql
max_notes = Note.select("DISTINCT ON (notes.contact_id) notes.*").joins("INNER JOIN (#{max_times}) max_times ON notes.contact_id = max_times.contact_id AND notes.created_at = note_created_at").where(contact_id: current_user.contact_ids)
max_notes.group_by(&:contact_id)
This uses DISTINCT ON to drop dups in case two notes have exactly the same contact_id and created_at values. If you aren't using PostgreSQL you'll need another way to deal with dups.