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I'm sure . i got error when i have 2 inner join cuz i test each of theme seperatly.
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Hi,
I am reviewing existing code and stumbled across something that, to me - and I'm new to ADO.NET, seems very awkward. A DataSet is filled using a OleDbDataAdapter. The weird thing is that the command does not affect any records at all, intentionally. It looks something like "SELECT ... WHERE 0 = 1".
The comment describing the method containing this code says "Retrieve an empty dataset that contains the database structure". DataSet Quick Whatch reports the dataset to be empty after the fill.
Does this SELECT statement really do any good? 
Thanks for comments, ideas or advise!
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I don't use datasets because they tend to encourage the data layer to get too close to the presentation layer (not good design). The SELECT statement returns, as you've already noticed, an empty set. But that isn't to say that nothing at all was returned. I'm guessing that the empty DataSet is subsequently used to look at the data schema without actually needing to get any data. Obviously, it would be wasteful to get data that isn't going to be used.
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This is usually a way to get an empty dataset with the correct stucture. It may be used for collecting and adding new rows to the database or perhaps merging data from another program layer before updating the database. I sometimes use this in large stored procedures which produce mutitable datasets; some of the tables may be empty, but my data layer expects the table structure to be there so I can add relationships, so I use a WHERE 0 = 1 to create an empty table.
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Thank you for your informative answer!
However, let's extend my question somewhat. I understand why someone would want to do this, and when to use it. What I don't understand is why this is done in light of what the code does next.
instanceDS = m_InstDb.GetInstanceDBDefinition();
string[] arl = new string[1];
arl[0]="T_Project";
instanceDS = m_InstDb.GetDataSetFromTables(arl);
Doesn't the fourth line of code overwrite what was initially in 'instanceDS'? If it does, then the first line should be superflous, or am I wrong? Does preparing 'instanceDS' do any good when its about to be assigned something else?
The first assignment to 'instanceDS' takes a long time (according a profiling tool I use), because the DataSet is "filled" with the structure of several tables, and my task as of now is to optimize the code for speed.
Grateful for more help!
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Yes, that's not great code. In the most optomistic light, it looks like it might have been introduced during modification of the code (where it might have been used before the re-assignment). In the worst case, I would check if the variable instanceDS has a scope wider than the local procedure and make sure it is not used from within GetDataSetFromTables(). That would be REALLY bad. Also check that no other objects are affected from within GetInstanceDBDefinition(); it might be modifying some properties for later use(side effects).
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Hi,
I've just started working with ADO.NET, through which I read from and update a MS Access data base. Now, what I want to do is to first update exactly one row in a data base, and then retrieve the updated row. Currently, this is performed in two steps. However, I want to reduce these two steps into one batch statement like this "UPDATE....; SELECT...." to increase performance.
OleDbCommand.ExecuteReader() throws an exception saying "Characters found after end of SQL statement.". What does this mean? I have tried to google my way to an answer, but I get mixed messages and become more and more confused the more I read.
Is it possible to batch several statements, and query them on the same connection using MS Access? This is where people seem to disagree.
Also, I can't use a stored procedure (which would be ideal btw), because the SELECT-statement returns a value, and that's not possible with MS Access  .
Any help and/or suggestions would be much appreciated!
Thanks
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I have your problem too.
So i had to execute each statement seperatly to work e.g to insert a row and get its ID :
oleDbCommand = new OleDbCommand ( "insert into myTable ... " , oleDbConnection );
.
.
.
add parameters
oleDbCommand.ExecuteNonQuery();
oleDbCommand = new OleDbCommand ( "select @@IDENTITY" , oleDbConnection );
int retValue = Convert.ToInt16( oleDbCommand.ExecuteScalar() );
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I've just learned that Access can't handle batching of statements, whereas SQL Server (probably among others) does. In other words, another weekness of MS Access, which I'm terribly stuck with 
Thank you for your comment anyway!
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hi
i want to connect to a sql database from a stored procedure of another sql database and insert data into a table.
shelly
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Hello friends!
I want to change the owner of the object
I have table whose owner is dbo but i want to change it to hov
can u please tell me complete syntax of that
Also when we right click on table and select design table , here we find menu like Trigger then Show permission then show dependency like that
If I chose show permission here we find list all users/userdefined database roles/public like that , can u please explain that thing (window) to me what that mean by?
T.I.A
Shashank
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What are you talking about ? I got to Design Table in SQL Server, then I could not follow your instructions - are you using SQL Server, or something else ?
Not that you need to use SQL Server, but you could provide at least some clue, seeing as your question is not about SQL, ADO, or ADO.NET.
Christian Graus - Microsoft MVP - C++
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under2811Hi
I am asking two thing first is how to change owner of a table
i.e. I have table whose owner is 'dbo' and now I want to change owner dbo to owner 'hov'
How to change that???
second thing i asked if we open E.M here we find lots of table suppose if I right click on one table say employees then we get menus like new table,design table,open table like that if i cliked on design table , we find another more menus like set primary keys,triggers,show permissions like that now i want to know what this term 'show permission' is???
please explain in detail
shashank
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Ah, I see. It shows the users of the database, and what permissions each of them has in regard to that table.
Or, if you don't know what it is, don't mess with it 
The answer to question 1 is probably sp_changeobjectowner. Look it up in the SQL Server books that come with the product.
Christian Graus - Microsoft MVP - C++
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I don't know how to do it from enterprize manager, but you can run sp_changeobjectowner from query analyzer to change the ownership of a table.
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I got an application connected to a piece of local MS Access database.
My goal is to get results of 50 count numbers from a table.
So what I did is
1)Create a stored procedure in Access "parameter ... select count(*) from table between '$inputA' and '$inputB'". Test it in Access,and it works well to get correct results.
2)In my C# application I create a oledbconnection with Access file and set the command type to be storedprocedure, then call it using executeScaler with different input parameters for 50 times.
It seems the performance is so slow
Is there anyone with better logic to improve this design and make the program faster?
Thanks
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What kind of data is in the table?
What is the primary key for the table?
How many rows in the table?
what is the data type for the input parameters?
how many other columns in the table (the query doesn't look syntactically correct- shouldn't it be "select count(*) from [tablename] where [columnname] between..."
What were the timing results (and on what platform), and what were your expectations.
In other words, a little more info might help someone help you... Perhaps even some example code (closing and re-opening the connection on every iteration can be a performance killer...)
Absolute faith corrupts as absolutely as absolute power
Eric Hoffer
The opposite of the religious fanatic is not the fanatical atheist but the gentle cynic who cares not whether there is a god or not.
Eric Hoffer
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There are two tables related to select statement: Logs and Users
Logs(3 columns) 1500 rows
LogID(auto number; it is the PK) room(number) LogTime dateTime
eg. 1 301 10/12/2004
Reserchers(3 columns) 3 rows
resID(auto number; it is the PK) room(number) project(text)
eg. 8722 301 ‘computer vision’
Stored procedure:
PARAMETERS startDate DateTime, endDate DateTime;
SELECT Count(*)
FROM Logs AS l, Researchers AS r
WHERE (((l.LogTime) Between [startDate] And [endDate])) And l.room=r.room And r.project='computer vision';
My desktop: CPU: PIII733; Memory 256MB
Development tools: VS.Net2003 and MS Access
In the application program I simply use a for loop with start date and end date decreasing.
Array.Add((int)this.odbCommand.ExecuteScalar());
After leave the connection open only once the main form is created then close it in the form's dispose method. I got timing results: 7 seconds to retrieve the 50 results, and I expect it takes less than one second.
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First, I would note that the autonumber columns are serving no useful purpose other than to satisfy Access's desire that you give a table a PK. They have no relation to the data in either table. Typically one would use an autonumber in one table as the foreign key in related tables to related data in different tables (in your case the related data seems to be the room number, so it might have made sense to used the resID from Researchers as a foreign key in the logs table instead of room number, this would at least have insured that all the records in Logs matched a record in Researchers - assuming that this is expected).
A join might make this a bit faster:
"select Count(*) from Logs as L inner join Researchers as R on L.room = R.room
Where r.project = 'computer vision' and L.Logtime >= [startDate] and L.LogTime <= [endDate]" (The >=/<= operators are equivalent to the Between operator, but could be faster depending on the SQL parser)
You should also create an index on the room and logdate fields in the Logs table ( in the field properties for each, change indexed to "Yes, duplicates allowed" )
using the System.data.oledb namespace equivalents may be faster than the system.data.odbc ones, the oledb stuff is newer, and likely more optimised for .Net and the Jet engine.
256 MB is a pretty small footprint these days, you may want to insure that you aren't page swapping. Also, access is a file based database, and not a very performant one at that, so your expectations could be a bit high. You're seeing about 140 ms per query and expecting > 20. Make sure the database is compacted before running your tests, if the database is internally fragmented (from a lot of development changes or data deletion) it could markedly effect the results.
Absolute faith corrupts as absolutely as absolute power
Eric Hoffer
The opposite of the religious fanatic is not the fanatical atheist but the gentle cynic who cares not whether there is a god or not.
Eric Hoffer
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i use some codeto search on access db
suppose on table T there is two fields ArtistID(Integer) , status(Text)
i got error on :
.
.
.
public string GetCOMMTXT()
{
string sql="select * from T whre";
int ArtistID = 5;
string Status = "A";
sql += "artistID = " + ArtistID + " " ;----> there is no Error
sql += "status = " + "'"+Status+"'";----> there is Error
or if i wrote
sql += "status = " +Status;----> there is Error
.
.
.
return sql;
}
what should i do?
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WDI wrote:
what should i do?
I'd fix the error.
First, the code you've presented here is not the code you've got a problem with because there are more errors in it than you present. For instance, the word "where" is misspelled.
Second, and I'm sure I've told you this before, you should use parameterised queries. Then you don't need to worry about stringing together fragments of SQL like this. And, it also improves the security of your application, reducing the risk that someone will be able to successfully launch an attack on it. For more information you can read SQL Injection Attacks and Tips on How to Prevent Them[^]. This acticle actually shows you how to use parameterised queries. I don't know why you don't use them. It makes everything so much easier.
Just for your information - I fully expect you to change this to use parameterised queries - The reason for the error is that you need to put an AND or OR between the conditions in a WHERE clause.
Another tip, put a breakpoint on the return statement and examine the contents of the sql string - it is much easier to read that than trying to decipher what the string should look like based on code that concatenates lots of little strings together.
Does this help?
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I do waht you told but get
Syntax error (missing operator) in query expression 'AND( styleID = @styleID )'.
my method is :
public static IDataReader GetFilteredProduct( FilterEN filterEN )
{
OleDbConnection oleDbConnection;
OleDbCommand oleDbCommand = new OleDbCommand();
OleDbDataReader oleDbDataReader = null;
oleDbCommand.CommandText = "select Product.productID , Product.productName ,
Product.productInfo , Product.productPrice ,
Product.dateOfInsert , Product.status ,
Product.artistID , Artist.artistName from Product
inner join Artist on Product.artistID =
Artist.artistID ";
oleDbConnection = new OleDbConnection (ConfigurationSettings.AppSettings["DbC"]);
try
{
oleDbConnection.Open();
string boolian = ( filterEN.Boolian == 1 ? "OR" : "AND" );
if ( filterEN.StyleID > 0 || filterEN.ArtistID > 0 )
{
oleDbCommand.CommandText += " where ";
}
if ( filterEN.StyleID > 0 )
{
oleDbCommand.CommandText += boolian + "( styleID = @styleID )";
OleDbParameter paramStyleID = new OleDbParameter ( "@styleID" ,
OleDbType.Integer );
paramStyleID.Value = filterEN.StyleID;
oleDbCommand.Parameters.Add ( paramStyleID );
}
if ( filterEN.ArtistID > 0 )
{
oleDbCommand.CommandText += boolian + "artistID = @artistID ";
OleDbParameter paramArtistID = new OleDbParameter ( "@artistID" ,
OleDbType.Integer );
paramArtistID.Value = filterEN.ArtistID;
oleDbCommand.Parameters.Add ( paramArtistID );
}
oleDbCommand.Connection = oleDbConnection;
oleDbDataReader = oleDbCommand.ExecuteReader(CommandBehavior.CloseConnection);
}
catch( Exception ex)
{
throw ex;
}
return oleDbDataReader;
}
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