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  • Returning IEnumerable<T> vs IQueryable<T>

    - by stackoverflowuser
    what is the difference between returning iqueryable vs ienumerable. IQueryable<Customer> custs = from c in db.Customers where c.City == "<City>" select c; IEnumerable<Customer> custs = from c in db.Customers where c.City == "<City>" select c; Will both be deferred execution? When should one be preferred over the other?

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  • DB2: Won't allow parameterize fetch first X rows only

    - by Guy Roth
    Although in Oracle DB its is allowed to parametrize the number of rows that the query can fetch by adding to the query: select ... from ... where ... and rownum <= @MaximumRecords I can't add similar condition to acuivalent query running in DB2: It is allowed to add: select ... from ... where ... fetch first 500 rows only (where there is fixed number of rows) but not: select ... from ... where ... fetch first :1 rows only (:1 == @MaximumRecords) Is someone aware of a solution/work-around to this problem?

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  • max count with joins

    - by trixet
    I have 3 tables: users: Id Login 1 John 2 Bill 3 Jim computers: Id Name 1 Computer1 2 Computer2 3 Computer3 4 Computer4 5 Computer5 sessions: UserId ComputerId Minutes 1 2 47 2 1 32 1 4 15 2 5 5 1 2 7 1 1 40 2 5 31 I would like to display this resulting table: Login Total_sess Total_min Most_freq_computer Sess_on_most_freq Min_on_most_freq John 4 109 Computer2 2 54 Bill 3 68 Computer5 2 36 Jim - - - - - Myself I can only cover first 3 columns with: SELECT Login, COUNT(sessions.UserId), SUM(Minutes) FROM users LEFT JOIN sessions ON users.Id = sessions.UserId GROUP BY users.Id And some kind of other columns with: SELECT main.* FROM (SELECT UserId, ComputerId, COUNT(*) AS cnt ,SUM(Minutes) FROM sessions GROUP BY UserId, ComputerId) AS main INNER JOIN ( SELECT ComputerId, MAX(cnt) AS maxCnt FROM ( SELECT ComputerId, UserId, COUNT(*) AS cnt FROM sessions GROUP BY ComputerId, UserId ) AS Counts GROUP BY ComputerId) AS maxes ON main.ComputerId = maxes.ComputerId AND main.cnt = maxes.maxCnt But I need to get whole resulting table in one query. I feel I'm doing something completely wrong. Need help.

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  • How to stop looking in a database after X rows are found?

    - by morningface
    I have a query to a database that returns a number X of results. I am looking to return a maximum of 10 results. Is there a way to do this without using LIMIT 0,9? I'll use LIMIT if I have to, but I'd rather use something else that will literally stop the searching, rather than look at all rows and then only return the top 10.

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  • MSSQL in ASP.NET application getting unstable after a certain period

    - by Barslett
    Hello, I have an ASP.NET 2.0 application that I made to keep track of disruption reports about our public transport system. The architecture is pretty straight-forward; an MSSQL Express 2008 database, ADO.NET and a DataSet/DAL with a few methods to access the database. There is a set of .aspx pages for the UI in use by our dispatchers and on our public website, as well as a set of SOAP and REST webservices and an RSS feed. Everything worked just fine for more than a year, until two weeks ago. Now and then, it seems as the database enters an unstable mode, and the application starts responding something right, something wrong. The typical error is that apparently, an empty DataTable is returned to the public disruption overview or to the RSS generator. Thus, the user gets e.g. an empty GridView, but no exception is thrown AFAIK, and nothing is written to the Windows Application log. After a restart of the MSSQL Express service, the situation is back to normal. It has to be said that the situation first time appeared a few days after I made a new minor upgrade of the application. The RSS generator was slightly rewritten, and I added a WCF REST service. But the DAL and the database schema were untouched... Any hints of how we could keep the database stable? It is a bit annoying not to have a clue ;-)

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  • Arrays in database tables and normalization

    - by Ivan Petrov
    Hi! Is it smart to keep arrays in table columns? More precisely I am thinking of the following schema which to my understanding violates normalization: create table Permissions( GroupID int not null default(-1), CategoryID int not null default(-1), Permissions varchar(max) not null default(''), constraint PK_GroupCategory primary key clustered(GroupID,CategoryID) ); and this: create table Permissions( GroupID int not null default(-1), CategoryID int not null default(-1), PermissionID int not null default(-1), constraint PK_GroupCategory primary key clustered(GroupID,CategoryID) ); UPD: Forgot to mention, in the scope of this concrete question we will consider that the "fetch rows that have permission X" won't be performed, instead all the lookups will be made by GroupID and CategoryID only Thoughts? Thanks in advance!

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  • collation in stored procedure

    - by Sharique
    I have a table which contains data in different languages. All fields are nvarchar(max). I created a stored procedure which trim values of all the fields Create Proc [dbo].[TrimValues] as update testdata set city = dbo.trim(city), state = dbo.trim(state), country = dbo.trim(country), schoolname = dbo.trim(schoolname) after trim all non-english text become ?????

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  • Varchar columns: Nullable or not.

    - by NYSystemsAnalyst
    The database development standards in our organization state the varchar fields should not allow null values. They should have a default value of an empty string (""). I know this makes querying and concatenation easier, but today, one of my coworkers questioned me about why that standard only existed for varchar types an not other datatypes (int, datetime, etc). I would like to know if others consider this to be a valid, defensible standard, or if varchar should be treated the same as fields of other data types? I believe this standard is valid for the following reason: I believe that an empty string and null values, though technically different, are conceptually the same. An empty, zero length string is a string that does not exist. It has no value. However, a numeric value of 0 is not the same as NULL. For example, if a field called OutstandingBalance has a value of 0, it means there are $0.00 remaining. However, if the same field is NULL, that means the value is unknown. On the other hand, a field called CustomerName with a value of "" is basically the same as a value of NULL because both represent the non-existence of the name. I read somewhere that an analogy for an empty string vs. NULL is that of a blank CD vs. no CD. However, I believe this to be a false analogy because a blank CD still phyically exists and still has physical data space that does not have any meaningful data written to it. Basically, I believe a blank CD is the equivalent of a string of blank spaces (" "), not an empty string. Therefore, I believe a string of blank spaces to be an actual value separate from NULL, but an empty string to be the absense of value conceptually equivalent to NULL. Please let me know if my beliefs regarding variable length strings are valid, or please enlighten me if they are not. I have read several blogs / arguments regarding this subject, but still do not see a true conceptual difference between NULLs and empty strings.

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  • MSSQL STOREDPROC SELECTING FROM A FIELD FROM 1 TABLE USING LIKE TO CREATE MORE THAN 1 COLUM IN A DAT

    - by djshortbus
    I have a ASPX.NET DataGrid and im trying to USE a select LIKE 'X'% from a table that has 1 field called location. im trying to display the locations that start with a certain letter (example wxxx,axxx,fxxx,) in different columns in my data grid. SELECT DISTINCT LM.LOCATION AS '0 LOCATIONS' , LM.COUNTLEVEL AS 'COUNTLEVEL' FROM SOH S WITH(NOLOCK) JOIN LOCATIONMASTER LM ON LM.LMID = S.LMID WHERE LM.COUNTLEVEL = 1 AND LM.LOCATION NOT IN ('RECOU','PROBLEM','TOSTOCK','PYXVLOC') AND LM.LOCATION LIKE '0%' SELECT DISTINCT LM.LOCATION AS 'A LOCATIONS' , LM.COUNTLEVEL AS 'COUNTLEVEL' FROM SOH S WITH(NOLOCK) JOIN LOCATIONMASTER LM ON LM.LMID = S.LMID WHERE LM.COUNTLEVEL = 1 AND LM.LOCATION NOT IN ('RECOU','PROBLEM','TOSTOCK','PYXVLOC') AND LM.LOCATION LIKE 'A%'

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  • How to display SUM fields from a detailed table in a master table

    - by max
    What is the best approach to display the summery of DETAILED.Fields in its master table? E.g. I have a master table called 'BILL' with all the bill related data and a detailed table ('BILL_DETAIL') with the bill detailed related data, like NAME, PRICE, TAX, ... Now I want to list all BILLS, without the details, but with the sum of the PRICE and TAX stored in the detail table. Here is a simplified schema of that tables: TABLE BILL ---------- - ID - NAME - ADDRESS - ... TABLE BILL_DETAIL ----------------- - ID - BILLID - PORDUCT_NAME - PRICE - TAX - ... The retrieved table row should look like this: BILL.CUSTOMER_NAME, BILL.CUSTOMER_ADDRESS, sum(BILL_DETAIL.PRICE), sum(BILL.DETAIL.TAX), ... Any sugguestions?

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  • Delete backup files older than 7 days

    - by rockbala
    Using osql command, SSQL backup of a database is created. It is saved to Disk. Then renamed to match the date of the day backup was taken. All these files are saved in a single folder all the time. for example: Batch1.bat does the following 1) Created backup.bak 2) renamed to backup 12-13-2009.bak (this is done by the combination of % ~ - etc to get the date parameter) This is now automated to take backup everyday by Task scheduler in Windows. Can the batch file also be modified to delete backup files older than 7 days? if so, how ? If it is not possible via batch file, other than manually deleting the files are there any other alternatives to automate the deleting job ? Thanks in advance, Balaji S

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  • SQLserver multithreaded locking with TABLOCKX

    - by WilfriedVS
    I have a table "tbluser" with 2 fields: userid = integer (autoincrement) user = nvarchar(100) I have a multithreaded/multi server application that uses this table. I want to accomplish the following: Guarantee that field user is unique in my table Guarantee that combination userid/user is unique in each server's memory I have the following stored procedure: CREATE PROCEDURE uniqueuser @user nvarchar(100) AS BEGIN BEGIN TRAN DECLARE @userID int SET nocount ON SET @userID = (SELECT @userID FROM tbluser WITH (TABLOCKX) WHERE [user] = @user) IF @userID <> '' BEGIN SELECT userID = @userID END ELSE BEGIN INSERT INTO tbluser([user]) VALUES (@user) SELECT userID = SCOPE_IDENTITY() END COMMIT TRAN END Basically the application calls the stored procedure and provides a username as parameter. The stored procedure either gets the userid or insert the user if it is a new user. Am I correct to assume that the table is locked (only one server can insert/query)?

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  • How do I write this MySQL query?

    - by CT
    I am working on an Asset DB using a lamp stack. In this example consider the following 5 tables: asset, server, laptop, desktop, software All tables have a primary key of id, which is a unique asset id. Every object has all asset attributes and then depending on type of asset has additional attributes in the corresponding table. If the type is a server, desktop or laptop it also has items in the software table. Here are the table create statements: // connect to mysql server and database "asset_db" mysql_connect("localhost", "asset_db", "asset_db") or die(mysql_error()); mysql_select_db("asset_db") or die(mysql_error()); // create asset table mysql_query("CREATE TABLE asset( id VARCHAR(50) PRIMARY KEY, company VARCHAR(50), location VARCHAR(50), purchase_date VARCHAR(50), purchase_order VARCHAR(50), value VARCHAR(50), type VARCHAR(50), notes VARCHAR(200))") or die(mysql_error()); echo "Asset Table Created.</br />"; // create software table mysql_query("CREATE TABLE software( id VARCHAR(50) PRIMARY KEY, software VARCHAR(50), license VARCHAR(50))") or die(mysql_error()); echo "Software Table Created.</br />"; // create laptop table mysql_query("CREATE TABLE laptop( id VARCHAR(50) PRIMARY KEY, manufacturer VARCHAR(50), model VARCHAR(50), serial_number VARCHAR(50), esc VARCHAR(50), user VARCHAR(50), prev_user VARCHAR(50), warranty VARCHAR(50))") or die(mysql_error()); echo "Laptop Table Created.</br />"; // create desktop table mysql_query("CREATE TABLE desktop( id VARCHAR(50) PRIMARY KEY, manufacturer VARCHAR(50), model VARCHAR(50), serial_number VARCHAR(50), esc VARCHAR(50), user VARCHAR(50), prev_user VARCHAR(50), warranty VARCHAR(50))") or die(mysql_error()); echo "Desktop Table Created.</br />"; // create server table mysql_query("CREATE TABLE server( id VARCHAR(50) PRIMARY KEY, manufacturer VARCHAR(50), model VARCHAR(50), warranty VARCHAR(50))") or die(mysql_error()); echo "Server Table Created.</br />"; ?> How do I query the database so that if I search by id, I receive all related fields to that asset id? Thank you.

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  • how to design a schema where the columns of a table are not fixed

    - by hIpPy
    I am trying to design a schema where the columns of a table are not fixed. Ex: I have an Employee table where the columns of the table are not fixed and vary (attributes of Employee are not fixed and vary). Nullable columns in the Employee table itself i.e. no normalization Instead of adding nullable columns, separate those columns out in their individual tables ex: if Address is a column to be added then create table Address[EmployeeId, AddressValue]. Create tables ExtensionColumnName [EmployeeId, ColumnName] and ExtensionColumnValue [EmployeeId, ColumnValue]. ExtensionColumnName would have ColumnName as "Address" and ExtensionColumnValue would have ColumnValue as address value. Employee table EmployeeId Name ExtensionColumnName table ColumnNameId EmployeeId ColumnName ExtensionColumnValue table EmployeeId ColumnNameId ColumnValue There is a drawback is the first two ways as the schema changes with every new attribute. Note that adding a new attribute is frequent. I am not sure if this is the good or bad design. If someone had a similar decision to make, please give an insight on things like foreign keys / data integrity, indexing, performance, reporting etc.

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  • Tentative date casting in tsql

    - by Tewr
    I am looking for something like TRYCAST in TSQL or an equivalent method / hack. In my case I am extracting some date data from an xml column. The following query throws "Arithmetic overflow error converting expression to data type datetime." if the piece of data found in the xml cannot be converted to datetime (in this specific case, the date is "0001-01-01" in some cases). Is there a way to detect this exception before it occurs? select [CustomerInfo].value('(//*:InceptionDate/text())[1]', 'datetime') FROM Customers An example of what I am trying to achieve in pseudocode with an imagined tsql function TRYCAST(expr, totype, defaultvalue): select TRYCAST( [CustomerInfo].value('(//*:InceptionDate/text())[1]', 'nvarchar(100)'), datetime, null) FROM Customers

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  • Avoiding Nested Queries

    - by Midhat
    How Important is it to avoid nested queries. I have always learnt to avoid them like a plague. But they are the most natural thing to me. When I am designing a query, the first thing I write is a nested query. Then I convert it to joins, which sometimes takes a lot of time to get right. And rarely gives a big performance improvement (sometimes it does) So are they really so bad. Is there a way to use nested queries without temp tables and filesort

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  • ASP.NET MVC Deployed Application Server Address

    - by Jacob Huggart
    I have an application that sends an email to a user so that they may access a web form. In the email there is just a link to the start page of this form. Currently, I have the value for the form location hardcoded. Once the app is deployed I know it is in inetpub/wwwroot/appName, which results in a URL of serverip:appPort/appName. What is the C# to get the serverip:appPort portion of the URL that I need? I think that server.mappath() might work, but for some reason I can't get to the method even though I have the necessary references.

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  • SqlServer2008 + expensive union

    - by Tim Mahy
    Hi al, we have 5 tables over which we should query with user search input throughout a stored procedure. We do a union of the similar data inside a view. Because of this the view can not be materialized. We are not able to change these 5 tables drastically (like creating a 6th table that contains the similar data of the 5 tables and reference that new one from the 5 tables). The query is rather expensive / slow what are our other options? It's allowed to think outside the box. Unfortunately I cannot give more information like the table/view/SP definition because of customer confidentiality... greetings, Tim

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  • LINQ Query returns nothing.

    - by gtas
    Why is this query returns 0 lines? There is a record matching the arguments. Deafkaw.Where(p => (p.ImerominiaKataxorisis >= aDate && p.ImerominiaKataxorisis <= DateTime.Now) && (p.Year == etos && p.IsYpodeigma == false) ).ToList(); Am i missing something?

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  • Accessing non-related entities in LinqToSql entity classes

    - by Chris Johnson
    In LinqToSql, if I want to access a non-related entity in an entity partial class, how do I do this without creating a new DataContext? Here's the scenario: I have the tables Client, IssueType and ClientIssueType. A Client may specify a list of IssueTypes if they do not want to use the default IssueTypes. I have the default IssueTypes in the ClientIssueType table with a ClientId of null. In my Client partial I'd like to try to retrieve all IssueTypes, and if none are found, return all default IssueTypes. The only way I can see of accessing the IssueTypes with a null ClientId is by accessing the table through a new DataContext, which is problematic once I want to start assigning them to Issues. Where am I going wrong?

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