For the sake of this question, let's assume I have tables 'A' and 'B' and there is a 1:1 relationship between them. In a Linq query, I can do the following:
from row in A
where row.B.Description = someValue
select A
Where row.B is the reference to table 'B'.
However, let's now assume there is a 1:M relationship between 'A' and 'B'. The above query no longer works. It seems I need to explicitly use 'join' as follows:
from row in A
join row1 in B on row.BId = row1.BId
where row1.Description = someValue
select A
My question is this. Am I correct that for 1:M relationships, 'join' is required? Or is there are way to do this query, without using join, like in the 1:1 case?
You don't have to join explicitly, select many will do the trick
from row in A
from row1 in row.B
where row1.Description == someValue
select row
alternatively (although I really don't like it)
from row in A
where row.B.Any(b => b.Description == someValue)
select row
With the first option you will need to do a Distinct() on the result if there are many B's that have the same description.
In theory, you should always use Join, if nothing else, then for clarity and readability. But in any 1:M case, you need to specify how the tables relate to each other. Just as you would have to do in SQL.
Related
i'm having a technical and syntax problem with JOINS in ORACLE.
If i have 7 tables, listed below:
FROM
QT_QTS.PLA_ORDEM_PRODUCAO pla,
qt_qts.res_tubo_austenitizacao aust,
qt_qts.res_tubo_revenimento1 res_rev1,
qt_qts.res_tubo_revenimento2 res_rev2,
limsprod.SAMPLE sp,
limsprod.test t,
limsprod.result r
I need to get ALL the data in the "limsprod.result r" table linked with similar corresponding data inside the qt_qts.res_tubo_austenitizacao aust, qt_qts.res_tubo_revenimento1 res_rev1 and qt_qts.res_tubo_revenimento2 res_rev2 tables.
How can I do this join using Oracle Database? I tried a left join, but it did not work.
It is impossible to answer that question. We have nothing but list of some tables. I'm not sure I'd even want to do that instead of you.
However, here's a suggestion: start with one table:
select * from limsprod.result r;
It'll return all rows. Then join it to another table:
select *
from limsprod.result r join qt_qts.res_tubo_austenitizacao aust on aust.id = r.id
and see what happens - did you get all rows you want? If not, should you add another JOIN condition? Perhaps an outer join? Don't move on to the third table until you sort that out. Once you're satisfied with the result, add another table:
select *
from limsprod.result r join qt_qts.res_tubo_austenitizacao aust on aust.id = r.id
join qt_qts.res_tubo_revenimento1 res_rev1 on res_rev1.idrr = aust.idrr
Repeat what's being said previously.
I have two tables: A, B.
A has prisoner_id and prisoner_name columns.
B has all other info about prisoners included prisoner_name column.
First I select all of the data that I need from B:
WITH prisoner_datas AS
(SELECT prisoner_name, ... FROM B WHERE ...)
Then I want to know all of the id of my prisoner_datas. To do this I need to combine information by prisoner_name column, because it's common for both tables
I did the following
SELECT A.prisoner_id, prisoner_datas.prisoner_name, prisoner_datas. ...,
FROM A, prisoner_datas
WHERE A.prisoner_name = prisoner_datas.prisoner_name
But it works very slow. How can I improve performance?
Add an index on the prisoner_name join column in the B table. Then the following join should have some performance improvement:
SELECT
A.prisoner_id,
B.prisoner_name,
B.prisoner_datas.id -- and other columns if needed
FROM A
INNER JOIN B
ON A.prisoner_name = B.prisoner_name
Note here that I used an explicit join syntax here. It isn't required, and the query plan might not change, but it makes the query easier to read. I don't think the CTE will change much, but the lack of an index on the join column should be important here.
TablePatient.Patient_ID(PK)
TableProviders.Encounter (joins to PK)
TableProviders.Provider_Type
TableProviders.Provider_ID
TableNames.Full_Name
TableNames.Provider_ID (joins to Table Names)
I want a query that will give, for all the Patient_IDs, the Full_Name of the provider for every Provider ID.
There are about 30 provider_types.
I have made this already using a left join a ton of left joins. It takes a long time to run and I am thinking there is a trick I am missing.
Any help?
Ok, my previous answer didn't match at all what you meant. You want to pivot the table to have on each line one Patient_ID with every Full_name for every provider_type. I assume that each patient has only one provider for one type and not more ; if more, you will have more than one row for each patient, and anyway I don't think it's really possible.
Here is my solution with pivot. The first part is to make it more understandable, so I create a table named TABLE_PATIENT in a subquery.
WITH TABLE_PATIENT AS
(
SELECT TablePatient.Patient_ID,
TableProviders.Provider_Type,
TableNames.Full_Name
FROM TablePatient LEFT JOIN
TableProviders on TablePatient.Patient_ID = TableProviders.Encounter
LEFT JOIN
TableNames on TableNames.Provider_ID = TableProviders.Provider_ID
group by TablePatient.Patient_ID,
TableProviders.Provider_Type,
TableNames.Full_Name
)
SELECT *
FROM TABLE_PATIENT
PIVOT
(
min(Full_name)
for Provider_type in ([type1], [type2],[type3])
) AS PVT
So TABLE_PATIENT just has many rows for each patient, with one provider each row, and the pivot puts everything on a single row. Tell me if something doesn't work.
You need to write every type you want in the [type1],[type2] etc. Just put them inside [], no other character needed as ' or anything else.
If you put only some types, then the query will not show providers of other types.
Tell me if something doesn't work.
If I understand what you mean, you just want to group the answer by Patient Id and then Provider ID. A full name is unique on a provider id right ?
This should be something like
SELECT TablePatient.Patient_ID,
TableProviders.Provider_ID,
TableNames.Full_Name
FROM TablePatient LEFT JOIN
TableProviders on TablePatient.Patient_ID = TableProviders.Encounter
LEFT JOIN
TableNames on TableNames.Provider_ID = TablerProviders.Provider_ID
group by TablePatient.Patient_ID,
TableProviders.Provider_ID,
TableNames.Full_Name
You can either group by TableNames.Full_Name or select First(TableNames.Full_Name) for example if indeed a full name is unique to a provider ID.
Note : I used the SQL server Syntax, there can be différences with Oracle ..
My question might seem weird. But I need to know whether we can identify and seggregate the rows fetched from particular table in a query, which is formed by joining tables.
Please refer the below query if I am you are not clear with my question.
My requirement is to know the rows fetched from table 'rel' alone in the query.
SELECT rel.*
FROM rel, C
WHERE rel.col1 = C.col1
AND C.col1 NOT IN (SELECT R.col1 FROM R WHERE R.col2 = 'MN')
AND rel.col2= 'MN'
AND rel.col3= 'MN'
AND c.col2 ='MN';
Thanks,
Savitha
Since you are performing an INNER JOIN by using the comparison in the WHERE clause, all your records, by definition, are coming from the rel table.
I have 2 tables which in simplified form look like this:
Products(
id: int,
name: varchar
);
ProductSpecs(
product_id: int,
spec_name: varchar,
spec_value: int
);
Now I need to sort products (in linq to sql) by value of some specification item (eg. "price"). So I do something like this
var products = from p in db.Products
from ps in p.ProductsSpecs
where ps.spec_name == "price"
orderby ps.spec_value
select p;
The problem is that if there's no such ProductSpec with spec_name "price" the product is not included at all. I can add these products with Union or Concat but this way the sorting of the first part is not preserved.
What is the best way to deal with this?
Thanks.
First, I would recommend that you either do this in pure SQL as a function or Stored Procedure and then access this through linq, or add a price column to your product table. It seems like price would be a normal attribute to add to all of your products even if that price is NULL.
SQL:
select p.*
from products p
left outer join productspecs ps on
p.id = ps.product_id
and ps.spec_name = 'Price'
order by ps.spec_value
With that said, here's the weird bit of LINQ that should work on your table (I might have some of the column names spelled incorrectly):
var products = from p in db.Products
join ps in (from pss in db.ProductSpecs
where pss.spec_name== "Price"
select pss
) on p.id equals ps.product_id into temp
from t in temp.DefaultIfEmpty()
orderby t.spec_value
select p;
I tested this on some tables setup like above and created 5 products, three with prices in different value orders and this LINQ ordered them just like the SQL above and returned the null result rows as well.
Hope this works!
In ordinary SQL, you'd use an LEFT OUTER JOIN. This preserves rows that appear in the left-hand table (the one listed first), even when there's no matching row in the right-hand table (the second one listed, and the one that is outer joined). You end up with nulls for the values that should be, but weren't, present in the right-hand table. So, the price for those items missing a price would appear as NULL.
What that translates to in LINQ to SQL is another matter.
You might care to think about whether it is reasonable to have products that do not have a price. You're emulating something called EAV - Entity, Attribute, Value - tables, and they are generally regarded as 'not a good thing'.
Can you not just do a simple join?
var products =
from p in db.Products
join ps in db.ProductSpecs on p.id equals ps.product_id
where ps.spec_name == "price"
orderby ps.spec_value
select p;