I am writing a stored procedure that executes several successive SELECT statements. When I execute this procedure via ADO.NET, my intention is to end up with a DataSet containing several DataTable objects. This behaves as expected.
I am currently relying on the order of the tables in the DataSet to match the order of the SELECT statements in the stored procedure, however there is really no significance in this order. The person who ultimately has to maintain the procedure shouldn't have to know the expected order of the results, nor should the person maintaining the application have to know the order of the statements in the procedure.
What I want to know is, is it possible to assign names to the result of each SELECT statement within the stored procedure itself, and then have these come through via ADO.NET (hopefully seamlessly) so that I can access each table by its name instead of its order?
e.g.
// populate DataSet with results from stored proc
DataSet ds = new DataSet();
dataAdapter.Fill(ds);
// now access one of the resulting DataTable via name
return ds.Tables["NamedResultFromTheProc"];
So, is there any way to achieve this? Or will I have to rely on the order of the SELECT statements and always access the desired table by its index?
I've not tried this but could you not change the structure of the stored proc so that you have a query returning the name of the table before each data query?
i.e.
select 'TableName';
select * from Table where 1 = 1;
then build the Dataset manually by creating tables and adding them in?
The tables returned by your query will be given the names "Table", "Table1", "Table2" etc.
You can add TableMappings to your DataAdapter before filling your DataSet to map them to your table names:
myAdapter.TableMappings.Add("Table", "MyTable1");
myAdapter.TableMappings.Add("Table1", "MyTable2");
myAdapter.TableMappings.Add("Table2", "MyTable3");
Unfortunately, I do not believe this is possible! I have a similar setup which gets DataSets from Stored Procedures, and after looking I gave up and resorted to indexes.
This is also not the best solution, but you could make the first column in your query be the table name:
Select 'Customer', CustomerID, CustomerName, CustomerAddress
From Customer
Where CustomerID = #CustomerID;
Select 'Orders', OrderID, OrderPrice, OrderDate
From Order O
Join Customer C on C.CustomerID = O.CustomerID
Where C.CustomerID = #CustomerID;
Select 'OrderItems', ItemID, ItemDescription, ItemPrice
From OrderItems I
Join Order O on O.OrderID = I.OrderID
Join Customer C on C.CustomerID = O.CustomerID
Where C.CustomerID = #CustomerID;
It is not possible, but its SQL "fault", not the fault of DataAdapter/Set, because result set does not carry the name of the table queried (nor is that discernibly possible if you use inner join) nor does the table adapter have a query from which to pick the name.
One method you can use is to first return a list of tables as Query#0 in the procedure, e.g.
select 'MyTable;MySecondTable;ThirdOrSo' as tables
followed by all other queries, then read index 0 table and this field, split/forloop to rename other tables in dataset. The maintainer would still need to know the mechanism but at least it gives him some freedom to reorganize..
I've been thinking about this as well and the only solution I can think of is to create temporary tables within the procedure and populate the results into there (naming the tables as you go).
I've not tried this yet because it doesn't feel like the right way to do it with having to get the results twice (query into temp table, query the temp table).
It would be really useful if you could just rename your result set in SQL in the same way you can rename "Column AS [Custom Column]"...
Related
first of all I am sorry if this question is too obvious, since I am quite new in SQL.
So, I have a list of IDs (variable, depending how many products the user chooses). And I want to check if all of them are in a table. If one of them is not, the result of the query should be null. If all of them are there, the result should be all the rows where those IDs are.
How can I do this?
Best regards,
Flavio
Do a LEFT JOIN from the list to the table on the ID field. You'll get a null if there is no record
You can even put a WHERE clause like 'WHERE List.ID IS NULL' to only see those that aren't in the table
Edit: Original Poster did not say they were using C# when I wrote this answer
UNTESTED:
Not sure if this is the most efficient but it seems like it should work.
1st it generates a count of items in the table for your list. Next it cross joins the 1 result record to a query containing the entire list ensuring the count matches the count in your provided list and limiting the results to your list.
SELECT *
FROM Table
CROSS JOIN (
SELECT count(*) cnt
FROM table
WHERE ID in (yourlist)) b
WHERE b.cnt = yourCount
and ID IN (YourList)
Running two in statements seems like it would be terribly slow overall; but my first step when writing SQL is usually to get something that works and then seek to improve performance if needed.
Get the list of Ids into a table, (you can pass them as a table variable parameter to a Stored proc), then in the stored proc, write
assuming the list of ids from C# is in table variable #idList
Select * from myTable
Where id in (Select id from #idList)
and not exists
(Select * from #idList
where id Not in
(Select id from myTable))
I am programming an Excel add-in in C# where I process data contained in different DataTable objects. I would like to provide a function to perform SQL queries on the data, with the ability to reference data from other tables in where and sort by clauses (for example, using a join).
An example of such a query would be
SELECT name
FROM Table1
WHERE id = Table2.id AND Table2.age > 18
The problem with this is that a DataTable doesn't know of the existance of the other DataTables, so (for so far I know) there are no such methods in the class. Also, I cannot use something like LINQ, since the query will be written by the users of the add-in in excel.
Would it be a good solution to copy the data to an in-memory database, where each DataTable is mapped to a table? How would this work performance-wise? Is there a simpler solution?
In terms of SQL query you are missing a table reference in selecting the tables, corrected query will look like
SELECT name
FROM Table1, Table2
WHERE Table1.id = Table2.id AND Table2.age > 18
Use Table1.name if there is same named attribute in Table2.
However using only WHERE condition in Joins without specifying the joining attribute is not recommended read this question. Use JOIN.
SELECT Table1.name
FROM Table1 INNER JOIN Table2 ON Table1.id = Table2.id WHERE Table2.age > 18
I've three tables
Investigators: id, name, first name
Articles: id, name, date
ArticlesInvestigators: id_Investigator, id_Articles, order
I want to get only all the investigators from the Investigators table to have one article published:
In SQL it would look like:
SELECT * FROM Investigators i, ArticlesInvestigators a
WHERE i.id = a.id_Articles
But how shall be in LINQ and lambda? Without join because only want the results of investigators table.
I don't know if i understand your question or not but try this way and tell us if it work or not :
1) you need to make FOREIGN KEY between your tables
2) do you query in C#
3) then you can get you data using the relation between your tables
I have a stored procedure that returns the table type. However, the EF model that has the stored procedure, only returns the present table class, but no associated classes. So when I traverse my referenced (child/parent) tables, I get nulls everywhere for those referenced table values.
I know this is expected as the stored procedure returns only that table (select * from that table), but I now would like to create a join clause AFTER calling the store procedure to get access to the rest of the referenced tables in my EF model.
Here is my code , slightly modified to make it easy to understand what I need...
var coll = db.SearchContacts(keyword,param1,param2)
//returns Contact types,works great
...now what I would like to do....(although I know syntax is off)
var ExtColl = coll join db.Address on coll.Address
join db.Department on coll.Department <- something similar
...so that I may now have access to that department (department.desc),
or address (address.civic) info from this contact.
I am at a loss as to how to implement this style of formatting AFTER I have already received it from the stored proc in the db.
Ok, so here is an update of what I am doing...
var ps = from d in db.SearchContacts(param1,param2)
select d.Id;
var p = from e in db.Contacts
.Include("Table1Ref")
.Include("Table2Ref")
.Include("Table3Ref")
Where(BuildOrExpression<DBMOdel.Contact,long>(e=>e.Id,ps.ToList()))
select e;
Now I am getting the return I want except for one thing....
there are tables that reference further referenced tables
that I would like to add, and Include does not allow
me to add them unto Contacts directly as these tables are not
referencing Contact but another table that references Contact
one layer/level further...so contacts references address
and address references province...
and I need to get access to the province info (such as description)
but need to finish my join statement properly....
So I am thinking of using join statement, but do not know the syntax for assigning or joining of this kind...
Contact -> Address on AdressId, Address -> Province on ProvinceId
SO i am thinking my linq statement would look like this...
var p = from e in db.Contacts
.Include("Table1Ref")
.Include("Table2Ref")
.Include("Table3Ref")
Where(BuildOrExpression<DBMOdel.Contact,long>(e=>e.Id,ps.ToList()))
-> join o in db.Province on o.ProvinceId equals e.Address.ProvinceId
select e;
but am not getting the desired effect...can anyone help?
I think I might be also mixing linq to sql or object with linq to entity...
this is the error I am getting for it
"The key selector type for the call to the 'Join' method is not comparable in the underlying store provider."
There is no SQL syntax to join tables to stored procedures, so EF won't be able to do this either.
Alternatives:
Do the joins in memory (linq to objects).
Do the joins in a stored procedure and map it to a complex type.
The latter option is likely to perform (much) better, but is less flexible. It's up to you to weigh the pros and cons.
I am a PHP/MySQL developer, slowly venturing into the realm of C#/SQL Server and I am having a problem in C# when it comes to reading an SQL Server query that joins two tables.
Given the two tables:
TableA:
int:id
VARCHAR(50):name
int:b_id
TableB:
int:id
VARCHAR(50):name
And given the query
SELECT * FROM TableA,TableB WHERE TableA.b_id = TableB.id;
Now in C# I normally read query data in the following fashion:
SqlDataReader data_reader= sql_command.ExecuteReader();
data_reader["Field"];
Except in this case I need to differentiate from TableA's name column, and TableB's name column.
In PHP I would simply ask for the field "TableA.name" or "TableB.name" accordingly but when I try something like
data_reader["TableB.name"];
in C#, my code errors out.
How can fix this? And how can I read a query on multiple tables in C#?
The result set only sees the returned data/column names, not the underlying table. Change your query to something like
SELECT TableA.Name as Name_TA, TableB.Name as Name_TB from ...
Then you can refer to the fields like this:
data_reader["Name_TA"];
To those posting that it is wrong to use "SELECT *", I strongly disagree with you. There are many real world cases where a SELECT * is necessary. Your absolute statements about its "wrong" use may be leading someone astray from what is a legitimate solution.
The problem here does not lie with the use of SELECT *, but with a constraint in ADO.NET.
As the OP points out, in PHP you can index a data row via the "TABLE.COLUMN" syntax, which is also how raw SQL handles column name conflicts:
SELECT table1.ID, table2.ID FROM table1, table;
Why DataReader is not implemented this way I do not know...
That said, a solution to be used could build your SQL statement dynamically by:
querying the schema of the tables you're selecting from
build your SELECT clause by iterating through the column names in the schema
In this way you could build a query like the following without having to know what columns currently exist in the schema for the tables you're selecting from
SELECT TableA.Name as Name_TA, TableB.Name as Name_TB from ...
You could try reading the values by index (a number) rather than by key.
name = data_reader[4];
You will have to experiment to see how the numbers correspond.
Welcome to the real world. In the real world, we don't use "SELECT *". Specify which columns you want, from which tables, and with which alias, if required.
Although it is better to use a column list to remove duplicate columns, if for any reason you want *****, then just use
rdr.item("duplicate_column_name")
This will return the first column value, since the inner join will have the same values in both identical columns, so this will accomplish the task.
Ideally, you should never have duplicate column names, across a database schema. So if you can rename your schema to not have conflicting names.
That rule is for this very situation. Once you've done your join, it is just a new recordset, and generally the table names do go with it.