My colleague asked me a question regarding getting data from a SQL Server database.
I have a sample data set
[ID],[TOWN],[PERSON]
[1],[BELFAST],[JAMES]
[2],[NEWRY],[JOHN]
[3],[BELFAST],[SIMON]
[4],[LARNE],[ALAN]
Now from this I would like to return a SQL Dataset that returns me a different table based upon the view.
Essentially in code I could get a distinct on the town then loop sql filtering on the town. But is there a way I can do this in SQL?
Where I would get (3) views back (2 Belfast, 1 Newry and 1 Larne)
Basicly I it would return
[ID],[Town],[Person]
[1],[Belfast],[James]
[3],[Belfast],[Simon]
Then another view would return for 'Larne' and a Final one for Newry. Basically SQL creating views for each town it finds and then returns the records for each town.
You don't get views back - you have to define them yourself.
E.g. if you need one view for Belfast, a second for Newry and a third for Larne - then you need to create three views that return only those rows that match the relevant city name
CREATE VIEW BelfastView
AS
SELECT ID, Town, Person
FROM dbo.Towns
WHERE Town = 'Belfast'
CREATE VIEW LarneView
AS
SELECT ID, Town, Person
FROM dbo.Towns
WHERE Town = 'Larne'
CREATE VIEW NewryView
AS
SELECT ID, Town, Person
FROM dbo.Towns
WHERE Town = 'Newry'
Now, certain users might only be allowed to select data from the BelfastView and thus would never see any other rows of data from your underlying table.
But views are database objects like tables or stored procedures; you need to create them, maintain them, toss them when no longer needed.
EDIT
Based on your updated question, you simply need to create a view for each town you want to filter:
CREATE VIEW BelfastView AS
SELECT ID,
Town,
Person
FROM YourTable
WHERE Town = 'BELFAST'
Although you've only given us a small sample of your data, what you're asking is almost never a good idea. What happens when you have 50 new towns in your DB? Are you going to create a view for each town? This does not scale well (or at all).
Basically I have decided to Run it as a Stored Procedure to return me each item as a List. So something along the lines of this:
Create Procedure ListTowns
As
declare #towns char(11)
select #towns = (select distinct Town from [Towns])
while #towns is not null <> 0
begin
select * from [YourTable] where Town = #towns
end
Related
If anyone could even just help me phrase this question better I'd appreciate it.
I have a SQL Server table, let's call it cars, which contains entries representing items and information about their owners including car_id, owner_accountNumber, owner_numCars.
We're using a system that sorts 'importantness of owner' based on number of cars owned, and relies on the owner_numCars column to do so. I'd rather not adjust this, if reasonably possible.
Is there a way I can update owner_numCars per owner_accountNumber using a stored procedure? Maybe some other more efficient way I can accomplish every owner_numCars containing the count of entries per owner_accountNumber?
Right now the only way I can think to do this is to (from the c# application):
SELECT owner_accountNumber, COUNT(*)
FROM mytable
GROUP BY owner_accountNumber;
and then foreach row returned by that query
UPDATE mytable
SET owner_numCars = <count result>
WHERE owner_accountNumber = <accountNumber result>
But this seems wildly inefficient compared to having the server handle the logic and updates.
Edit - Thanks for all the help. I know this isn't really a well set up database, but it's what I have to work with. I appreciate everyone's input and advice.
This solution takes into account that you want to keep the owner_numCars column in the CARs table and that the column should always be accurate in real time.
I'm defining table CARS as a table with attributes about cars including it's current owner. The number of cars owned by the current owner is de-normalized into this table. Say I, LAS, own three cars, then there are three entries in table CARS, as such:
car_id owner_accountNumber owner_numCars
1 LAS1 3
2 LAS1 3
3 LAS1 3
For owner_numCars to be used as an importance factor in a live interface, you'd need to update owner_numCars for every car every time LAS1 sells or buys a car or is removed from or added to a row.
Note you need to update CARS for both the old and new owners. If Sam buys car1, both Sam's and LAS' totals need to be updated.
You can use this procedure to update the rows. This SP is very context sensitive. It needs to be called after rows have been deleted or inserted for the deleted or inserted owner. When an owner is updated, it needs to be called for both the old and new owners.
To update real time as accounts change owners:
create procedure update_car_count
#p_acct nvarchar(50) -- use your actual datatype here
AS
update CARS
set owner_numCars = (select count(*) from CARS where owner_accountNumber = #p_acct)
where owner_accountNumber = #p_acct;
GO
To update all account_owners:
create procedure update_car_count_all
AS
update C
set owner_numCars = (select count(*) from CARS where owner_acctNumber = C.owner_acctNumber)
from CARS C
GO
I think what you need is a View. If you don't know, a View is a virtual table that displays/calculates data from a real table that is continously updated as the table data updates. So if you want to see your table with owner_numCars added you could do:
SELECT a.*, b.owner_numCars
from mytable as a
inner join
(SELECT owner_accountNumber, COUNT(*) as owner_numCars
FROM mytable
GROUP BY owner_accountNumber) as b
on a.owner_accountNumber = b.owner_accountNumber
You'd want to remove the owner_numCars column from the real table since you don't need to actually store that data on each row. If you can't remove it you can replace a.* with an explicit list of all the fields except owner_numCars.
You don't want to run SQL to update this value. What if it doesn't run for a long time? What if someone loads a lot of data and then runs the score and finds a guy that has 100 cars counts as a zero b/c the update didn't run. Data should only live in 1 place, updating has it living in 2. You want a view that pulls this value from the tables as it is needed.
CREATE VIEW vOwnersInfo
AS
SELECT o.*,
ISNULL(c.Cnt,0) AS Cnt
FROM OWNERS o
LEFT JOIN
(SELECT OwnerId,
COUNT(1) AS Cnt
FROM Cars
GROUP BY OwnerId) AS c
ON o.OwnerId = c.OwnerId
There are a lot of ways of doing this. Here is one way using COUNT() OVER window function and an updatable Common Table Expression [CTE]. That you won't have to worry about relating data back, ids etc.
;WITH cteCarCounts AS (
SELECT
owner_accountNumber
,owner_numCars
,NewNumberOfCars = COUNT(*) OVER (PARTITION BY owner_accountNumber)
FROM
MyTable
)
UPDATE cteCarCounts
SET owner_numCars = NewNumberOfCars
However, from a design perspective I would raise the question of whether this value (owner_numCars) should be on this table or on what I assume would be the owner table.
Rominus did make a good point of using a view if you want the data to always reflect the current value. You could also use also do it with a table valued function which could be more performant than a view. But if you are simply showing it then you could simply do something like this:
SELECT
owner_accountNumber
,owner_numCars = COUNT(*) OVER (PARTITION BY owner_accountNumber)
FROM
MyTable
By adding a where clause to either the CTE or the SELECT statement you will effectively limit your dataset and the solution should remain fast. E.g.
WHERE owner_accountNumber = #owner_accountNumber
I'm trying to implement a feature whereby, apart from all the reports that I have in my system, I will allow the end user to create simple reports. (not overly complex reports that involves slicing and dicing across multiple tables with lots of logic)
The user will be able to:
1) Select a base table from a list of allowable tables (e.g., Customers)
2) Select multiple sub tables (e.g., Address table, with AddressId as the field to link Customers to Address)
3) Select the fields from the tables
4) Have basic sorting
Here's the database schema I have current, and I'm quite certain it's far from perfect, so I'm wondering what else I can improve on
AllowableTables table
This table will contain the list of tables that the user can create their custom reports against.
Id Table
----------------------------------
1 Customers
2 Address
3 Orders
4 Products
ReportTemplates table
Id Name MainTable
------------------------------------------------------------------
1 Customer Report #2 Customers
2 Customer Report #3 Customers
ReportTemplateSettings table
Id TemplateId TableName FieldName ColumnHeader ColumnWidth Sequence
-------------------------------------------------------------------------------
1 1 Customer Id Customer S/N 100 1
2 1 Customer Name Full Name 100 2
3 1 Address Address1 Address 1 100 3
I know this isn't complete, but this is what I've come up with so far. Does anyone have any links to a reference design, or have any inputs as to how I can improve this?
This needs a lot of work even though it’s relatively simple task. Here are several other columns you might want to include as well as some other details to take care of.
Store table name along with schema name or store schema name in additional column, add column for sorting and sort order
Create additional table to store child tables that will be used in the report (report id, schema name, table name, column in child table used to join tables, column in parent table used to join tables, join operator (may not be needed if it always =)
Create additional table that will store column names (report id, schema name, table name, column name, display as)
There are probably several more things that will come up after you complete this but hopefully this will get you in the right direction.
I want to begin by stating I'm an SQL noob, so I'd appreciate any suggestions or comments on my workflow and/or mindset when trying to solve this issue.
What I'm doing is gathering usage statistics about several applications, in several categories (not all categories necessarily apply to all applications), storing them in a database.
I've set up a few tables to do that, and then one table to link everything together that's structured like so (from now on: Dtable):
(column name - details)
UserID - foreign key to another table which stores users data
ApplicationID - foreign key to another table which stores applications data
CategoryID - foreign key to another table which holds a list of different categories
Value - the actual data
Each application gathers the data, then submits it to the database using a stored procedure. As the amount of data can be different based on actual usage (not always sending every category) and for each application, I was thinking of sending the data as a DataTable with a list of CategoryID and Value so I won't have to call a procedure for every individual category (Ptable).
I need to update each record in Dtable to the correct value in Ptable according to CategoryID, but also filtered by UserID and ApplicationID. UserID and ApplicationID will be given as two other parameters to the Stored Procedure. Ptable only contains a list of CategoryID / Value records.
Now, I read about Cursors (for each record in the table parameter set the relevant data in the database table), but the consensus seems to be "Avoid at all costs".
How would I go about updating the table, then, based on the varying records in Ptable?
P.S.
The tables are structured like so to keep agility and scalability in adding more categories/applications in the future. If there's a better way to do it I'll be happy to know.
I believe the update statement would look something like this, where #ApplicationID and #UserID are the stored proc's other parameters:
update Dtable
set Dtable.Value = p.Value
from Ptable p
where Dtable.UserID = #UserID
and Dtable.ApplicationID = #ApplicationID
and Dtable.CategoryID = p.CategoryID;
I have run into a problem with a second trigger we are to write regarding the following:
I have just written a stored procedure and stored function that serve to insert a new row into my Orders table. The row update inserts: Ordernum, OrderDate, Customer, Rep, Manufacturer, Product, Qty, and SaleAmount.
I now have to write a trigger that updates my Offices table by adding the amount of the newly added sale. Problem is, not every salesrep has an office assigned to them. I don't understand if I need to have a when clause under 'FOR EACH ROW' which somehow stipulates this, or if I need to stipulate after my SET Sales line. This is my code so far, but unfortunately, it updates all of the offices sales, not just the one that the salesrep belongs to:
CREATE OR REPLACE TRIGGER UpdateOffices
AFTER INSERT ON Orders
FOR EACH ROW
BEGIN
UPDATE Offices
SET Sales = Sales + :NEW.Amount
WHERE Office IN (SELECT RepOffice
FROM Salesreps
WHERE RepOffice IS NOT NULL);
End;
/
SHOW ERRORS
Sales is the name of the column on the Offices table. Amount if the name used in the stored proc.
You've already been advised to add a predicate on Salesreps, e.g. WHERE Salesrep = :NEW.Rep. Why don't you add it to the subquery?
You are going to run into all sorts of problems implementing your solution using this trigger method.
The Office.Sales column value will become stale as soon as amendments to orders are committed to the database. For example, when the price or quantity on an order is changed or deleted.
I would recommend you implement this requirement as a 'Refresh on Commit' Materialized View.
Ok I have a question and it is probably very easy but I can not find the solution.
I have 3 tables plus one main tbl.
tbl_1 - tbl_1Name_id
tbl_2- tbl_2Name_id
tbl_3 - tbl_3Name_id
I want to connect the Name_id fields to the main tbl fields below.
main_tbl
___________
tbl_1Name_id
tbl_2Name_id
tbl_3Name_id
Main tbl has a Unique Key for these fields and in the other table, fields they are normal fields NOT NULL.
What I would like to do is that any time when the record is entered in tbl_1, tbl_2 or tbl_3, the value from the main table shows in that field, or other way.
Also I have the relationship Many to one, one being the main tbl of course.
I have a feeling this should be very simple but can not get it to work.
Take a look at SQL Server triggers. This will allow you to perform an action when a record is inserted into any one of those tables.
If you provide some more information like:
An example of an insert
The resulting change you would like
to see as a result of that insert
I can try and give you some more details.
UPDATE
Based on your new comments I suspect that you are working with a denormalized database schema. Below is how I would suggest you structure your tables in the Employee-Medical visit scenario you discussed:
Employee
--------
EmployeeId
fName
lName
EmployeeMedicalVisit
--------------------
VisitId
EmployeeId
Date
Cost
Some important things:
Note that I am not entering the
employees name into the
EmployeeMedicalVisit table, just the EmployeeId. This
helps to maintain data integrity and
complies with First Normal Form
You should read up on 1st, 2nd and
3rd normal forms. Database
normalization is a very imporant
subject and it will make your life
easier if you can grasp them.
With the above structure, when an employee visited a medical office you would insert a record into EmployeeMedicalVisit. To select all medical visits for an employee you would use the query below:
SELECT e.fName, e.lName
FROM Employee e
INNER JOIN EmployeeMedicalVisit as emv
ON e.EployeeId = emv.EmployeeId
Hope this helps!
Here is a sample trigger that may show you waht you need to have:
Create trigger mytabletrigger ON mytable
For INSERT
AS
INSERT MYOTHERTABLE (MytableId, insertdate)
select mytableid, getdate() from inserted
In a trigger you have two psuedotables available, inserted and deleted. The inserted table constains the data that is being inserted into the table you have the trigger on including any autogenerated id. That is how you get the data to the other table assuming you don't need other data at the same time. YOu can get other data from system stored procuders or joins to other tables but not from a form in the application.
If you do need other data that isn't available in a trigger (such as other values from a form, then you need to write a sttored procedure to insert to one table and return the id value through an output clause or using scope_identity() and then use that data to build the insert for the next table.